Measurements, test equipment and simulation

Evaluation method and design philosophy

Answers on this topic

• Do measurements tell you how good a DAC sounds, and is Rob an objectivist or a subjectivist?
• What is noise floor modulation, how does Rob measure it, and why does he say it is audible below what can be measured?
• Why does Rob design to -301 dB, how can that be verified, and how does small-signal accuracy relate to depth?

Everything he said on this topic (254)

One-line summaries in our words, oldest first. Each link opens the original.

• 2014-04-29After a joke, Watts reports a microphonics test: board tapping was not badly microphonic, tapping the crystal oscillator gave noise at -115dB, so vibration should not matter. Head-Fi, Apr 2014
• 2014-04-29Watts says Chord supplies precision-soldered prototypes, SPICE simulation meant only 4 components changed, the DAC hit its calculated 120 dB dynamic range, and Christmas went on FPGA coding. Head-Fi, Apr 2014
• 2014-07-02Watts rebuts a poster: he consults for silicon companies, Hugo's 16 cores at 208 MHz dwarf ASIC DACs, and FFTs at -40 and -140 dB show no distortion or NFM. Head-Fi, Jul 2014
• 2015-01-28Watts says the impedance may vary by a few milliohms with PCB tracking, measured by loading and unloading the headphone output while reading voltage at the RCA. needs context Head-Fi, Jan 2015
• 2015-04-21Watts says every Hugo he measured shows 120 dB dynamic range within 0.1 dB, but sensitive SE846 earphones will hiss, so use their attenuator. Head-Fi, Apr 2015
• 2015-05-20Watts says decimation is fine if followed by a WTA filter, but 140 dB decimation accuracy proved insufficient: non-decimating versions sound noticeably better and measurements show distortion at -140 dB. HIFICLUBE.NET JVH 3:52
• 2015-05-20Watts says that when you look at it, you do a digital simulation. needs context HIFICLUBE.NET JVH 7:08
• 2015-05-20Watts says the 350 dB is actual digital-domain performance: a 48-bit perfect sine feeds the noise shaper, and an FFT of the summed pulse array elements shows 350 dB in-band. HIFICLUBE.NET JVH 7:13
• 2015-06-27Watts defines noise floor modulation, says it is audible at immeasurable levels, and shows APx555 plots of Dave with an unchanged noise floor near -180dB with and without signal. Head-Fi, Jun 2015
• 2015-06-27Watts says the measurement used a 1.2M FFT at 48kHz, total noise is about -130dB A-weighted, and resolving a -180dB floor exposes small errors. needs context Head-Fi, Jun 2015
• 2015-07-19Watts reports APx555 measurements showing identical dynamic range across Hugo's inputs, optical slightly worse THD despite sounding better, and no source jitter artifacts down to 500 fS. Head-Fi, Jul 2015
• 2015-07-31Watts gives crosstalk of 120dB, distortion below -150dB and 21-bit noise, says such numbers do not show sound quality, and compares headphone drive with TT. Head-Fi, Jul 2015
• 2015-11-23Watts says USB is Dave's best input by a tiny margin, then optical, and gives measurements: 6.8v RMS at 1% THD into 300 and 33 ohms, 55 milliohm output impedance. Head-Fi, Nov 2015
• 2015-12-27Watts says he will find out at CES, and worries that without an APx555 one ends up measuring the test equipment; even with one it needs extreme care. needs context Head-Fi, Dec 2015
• 2015-12-30Watts says Dave sets a new benchmark in soundstage and measurements, criticizes reviewers who dismiss measured distortion as inaudible, and says removing any measurable distortion improves sound. Head-Fi, Dec 2015
• 2016-01-02Watts presents an APx555 J-test of Dave's USB input at 48 kHz: no data-related jitter, a -170 dB floor implying under 0.1 pS, and 0.2 pS mains jitter probably from the analyzer. Head-Fi, Jan 2016
• 2016-01-17Watts says all FIR filters need an overload margin for Gibbs phenomena, which his designs have had for twenty years, tested with 0 dBFS noise and square waves. Head-Fi, Jan 2016
• 2016-01-18Watts says the target is no out-of-band noise; Hugo is 50 kHz -3 dB, with no measurable noise from 23 to 50 kHz on CD; 1 MHz noise matters more. Head-Fi, Jan 2016
• 2016-01-29Watts gives DAVE's noise as -127 dB A-weighted at 2.5 V and distortion 0.000015 percent, and says his converters' distortion falls with signal level, unlike ladder, DSD or chip DACs. article, Jan 2016
• 2016-01-29Watts shows an APx555 plot with a -180 dB noise floor identical with no signal and at 2.5 V, and says noise floor modulation makes sound brighter and harder. article, Jan 2016
• 2016-02-14Watts says dynamic range only shows residual hiss; Dave has a -180 dB noise floor with no measurable noise floor modulation or small-signal distortion, which matter more. Head-Fi, Feb 2016
• 2016-02-25Watts says he is designing an ADC to match Dave, and shows a Verilog simulation of Dave's noise shaper reproducing a -301 dB sine over a -380 dB floor. Head-Fi, Feb 2016
• 2016-03-13Watts explains AES17 dynamic range, gives Dave's 2.6 uV residual (-128.4 dB re 6.8 V, -117.7 dB re 2 V), and says its unchanging noise shows no noise floor modulation. Head-Fi, Mar 2016
• 2016-03-13Watts says Hi-Fi News made no mistake quoting noise re 2 V, though methods confuse readers, which is why he gives uV, and notes it confirmed Dave's 0.000007% distortion. Head-Fi, Mar 2016
• 2016-04-12Watts gives DAVE's first-stage WTA response as +0.000003 dB at 23 kHz, cites 166 DSP cores at 0.1 TIPS, and calls ringing a red herring for judging timing. Head-Fi, Apr 2016
• 2016-07-24Watts says a major code rewrite, with more powerful simulation tools, was intended for a planned reference DAC; he made Hugo for hotel listening, expecting few sales. Hifistatement 1:17
• 2016-07-24Watts lists DAVE's measured performance: distortion and noise 124 dB A-weighted at 5 volts, minus 127 dB at 2.5 volts, dynamic range minus 127 dB, distortion 0.000015%. Hifistatement 0
• 2016-07-24Watts says the APx555, out the previous November, is the only equipment able to measure DAVE, which nears its levels; he cannot say how much is DAVE versus the AP. Hifistatement 0
• 2016-07-24Watts says DAVE's harmonics are below -150 dB and noise floor -180 dB, unchanged with no signal or 2.5 volts output; he says noise floor modulation sounds brighter and harder. Hifistatement 22
• 2016-08-28Watts compares DAVE and Mojo: 1% output into 300 ohms 6.8 V vs 5.4 V, THD+N at 3 V 0.00009% vs 0.00017%, THD at 2.5 V 0.000007% vs 0.0001%. Head-Fi, Aug 2016
• 2016-09-01Watts explains DAVE's output amplifier is a second-order analog noise shaper, so loading barely changes distortion and HF distortion stays low (1 GHz gain-bandwidth), citing 19k/20k test results. Head-Fi, Sep 2016
• 2016-09-13Watts clarifies that the -350 dB figure is the noise shaper's exact Verilog-simulated digital performance, mattering for preserving tiny signal amplitudes rather than noise, which he ties to depth. Head-Fi, Sep 2016
• 2016-09-26Watts points to DAVE's J-test, where skirting at -160 dB spans about +/- 20 Hz, about 1 pS of 20 Hz jitter, dominated by the APx555; worse skirting sounds brighter. Head-Fi, Sep 2016
• 2016-10-20Watts shows an FFT of DAVE's noise shaper output resolving a -301 dB 6 kHz signal, stands by his listening-based claim that depth needs this, and plans Davina tests. Head-Fi, Oct 2016
• 2016-12-08Watts says the quoted figures are nonsense and begins to give Hugo's actual output, but the figures that followed are missing from the record. needs context Head-Fi, Dec 2016
• 2017-02-13Watts says interpolated transient timing depends on sample timing unless the filter is ideal, and plans a Davina null test with half-sample-delayed white noise to measure the error. Head-Fi, Feb 2017
• 2017-04-05Watts says the red spectrum predated late January changes, a -177 dB noise floor exposes distortion other DACs hide, and a 16-bit test shows only tiny second and third harmonics. Head-Fi, Apr 2017
• 2017-04-05Watts describes his 16-bit distortion test: 0 dBFS at 2.65 V RMS into 300 ohms via optical, 5.3 V RMS reference, and no measured or audible charger effect. Head-Fi, Apr 2017
• 2017-05-12Watts says a remeasured DAVE was perfect on an APx555, suspects aliasing in JA's analyzer ADCs, and says Davina has zero noise floor modulation and around 15 dB less noise. Head-Fi, May 2017
• 2017-05-25Watts explains why pulse array DACs are jitter immune, why femto clocks with PLLs degrade sound, and how a Hugo 2 prototype jitter and element-mismatch test exposed a layout fault. Head-Fi, May 2017
• 2017-06-11Watts says DAVE sounds better via the M scaler not from a WTA fault, citing Verilog simulation and -301 dB tests, and video mode's two-thirds million taps shrinks the soundstage. Head-Fi, Jun 2017
• 2017-06-11Watts says a planned Davina test will give a measured number for the transient error, though not why taps above 0.66M improve the soundstage, which is perceptual. Head-Fi, Jun 2017
• 2017-06-18Watts says Hugo 2's digital DC servo keeps bass flat with crossfeed off, and APx555 peak measurements show 20 Hz to 1 kHz flat within 0.001 dB; DAVE is identical. Head-Fi, Jun 2017
• 2017-07-10Watts says open loop output impedance governs load response, now +/- 0.1 dB at 8 ohms and +/- 0.05 dB unloaded; measuring must allow for 34 mS WTA latency. Head-Fi, Jul 2017
• 2017-10-13Watts says Davina tests at zero noise floor modulation versus about 4 to 5 dB in standard ADCs, and that the APx555 uses four ADCs and a notch filter to avoid it. miceblue425 39:02
• 2017-10-13Watts says measurements must be right and give certainty; improving them, all else equal, has always improved sound, while some designers use distortion to change the sound. miceblue425 50:53
• 2017-10-16Watts posts seminar measurement slides, saying simulation shows -301 dB signals reproduced, his designs have no measurable noise floor modulation, and jitter FFTs should replace marketing claims. Head-Fi, Oct 2017
• 2017-10-20Watts says small-signal integrity was verified by passing the -301 dB test, so he cannot explain why longer taps change depth, which he has tied to small-signal integrity. Hifistatement 3:43
• 2017-10-23Watts says Hugo 2's battery is not bypassed; a regulated boost PSU replaced Hugo's super caps, cutting PSU distortion 10,000 times, and a linear PSU is inaudible with headphones. Head-Fi, Oct 2017
• 2017-12-05Watts lists distortion, small-signal nonlinearity and noise floor modulation as transparency factors; measuring with a minus 60 dB signal, most DACs reach about minus 60 dB, his about minus 175. RMAF 9:53
• 2017-12-05Watts says he once doubted distortion below minus 120 dB mattered, but while designing DAVE he pursued much lower distortion because reduced distortion had always sounded better. RMAF 12:58
• 2017-12-05Watts says DAVE prototypes stalled at minus 120 then minus 130 dB distortion, while he aimed to beat the dCS Vivaldi's minus 130, until one idea cut 20 dB. RMAF 13:41
• 2017-12-05Watts says since the 1990s he has found fundamental linearity affects depth perception, and defines the test: set minus 60 dB, play a minus 100 dB signal, measure its amplitude. RMAF 17:37
• 2017-12-05Watts says the signal would measure minus 102 or minus 98, with up to 2 or 3 dB error in the early days, visible as humps in fundamental linearity tests. RMAF 18:22
• 2017-12-05Watts says pulse array eliminated the fundamental linearity problem of his 1990s DSD256 DACs; a minus 120 dB signal now measures within a thousandth of a dB, Mojo to DAVE. RMAF 18:43
• 2017-12-05Watts concludes that what matters is the jitter measured at the DAC's output, not the clock's jitter level, then introduces chip DACs. RMAF 29:18
• 2017-12-05Watts says pulse array needs no resistor matching; a DC test shows resistor tolerance and clock jitter degrade the 126 dB noise figure by only half a dB. RMAF 42:18
• 2017-12-05Watts says measurements must be interpreted correctly but skipping them throws the baby out with the bathwater, and he uses the APx555. RMAF 47:59
• 2017-12-05Watts says he listens only after thorough measurement, and shows DAVE with noise floor modulation eliminated at 2.5 volts and harmonics below minus 150 and minus 155 dB. RMAF 48:25
• 2017-12-05Watts says every Verilog module must pass a minus 301 dB signal unchanged, about 60-bit accuracy he considers needed for depth, and DAVE's noise shaper shows minus 300.99 dB. RMAF 49:13
• 2017-12-05Watts says the 0.01 dB error is an FFT residual, and DAVE's noise at 100 kHz is minus 200 dB, whereas DSD's high out-of-band noise causes problems for analog electronics. RMAF 49:58
• 2017-12-05Watts shows a jitter test with no visible jitter, says Mojo nearly matches DAVE, and credits DAVE's low 19/20 kHz two-tone distortion to its second-order analog noise shaper amplifier. RMAF 50:44
• 2017-12-05Watts shows two 16-bit level signals with identical left and right ringing from the digital filter, calling it perfect 16-bit reproduction, then tries a 32-bit LSB signal. RMAF 52:07
• 2017-12-05Watts says a special method on the Audio Precision measured it within 1 dB, an error he attributes to the analyzer since every product shows it, then invites questions. needs context RMAF 52:57
• 2017-12-05Watts says no change is measurable from the 16FS to 256FS WTA filter, but the HF filter (green or red) adds -1dB at 20kHz. Head-Fi, Dec 2017
• 2017-12-05Watts says the change would not show in frequency-domain measurements at 192 kHz but would in a 16FS impulse response, needing 768 kHz test gear that does not exist. needs context Head-Fi, Dec 2017
• 2017-12-09Watts says he tests from no load to 8 ohms for a headphone DAC and from no load to 1 ohm for loudspeaker amps. article, Dec 2017
• 2017-12-26Watts says the industry is wrong to judge digital sound with non-bandwidth-limited impulses, and that pre-ringing diagrams make easy marketing. Audiophile Style, Dec 2017
• 2017-12-31Watts describes his method: identify an aberration, test its audibility by listening, reduce it until inaudible, using simulation to -300 dB, aiming to close the gap to live music. Head-Fi, Dec 2017
• 2018-01-10Watts lists noise and distortion pass criteria, says Hugo 2 and Qutest are within 0.5 dB of theoretical noise, and explains setting pulse array resistors at a distortion tipping point. Head-Fi, Jan 2018
• 2018-01-10Watts says the quartz oscillator and some parts are slightly microphonic: clicks are audible when the PCB is struck, and a mounting screw couples the oscillator to the chassis. Head-Fi, Jan 2018
• 2018-01-17Watts says Qutest's noise is identical at every output setting and the 3V figure reflects distortion; the best setting depends on the amp, e.g. 1v for a 1.2v-rated amp. Head-Fi, Jan 2018
• 2018-01-18Watts says the 0.025 ohm output impedance figure is incorrect as it has not been measured; the 300 ohm load represents the worst-case amp input impedance. Head-Fi, Jan 2018
• 2018-01-18Watts says 300 ohms is the measurement load, not the minimum load impedance, and the output impedance is too small to matter. Head-Fi, Jan 2018
• 2018-01-19Watts reports measuring Qutest's output impedance at 0.042 ohms at the phono sockets at 1kHz and 20Hz, with no coupling capacitor thanks to the digital DC servo. Head-Fi, Jan 2018
• 2018-01-22Watts describes a planned transient-error measurement, fearing 164,000 versus 1M taps may measure small, and recounts how cutting Dave's harmonics from -130dB to -150dB was unexpectedly audible. Head-Fi, Jan 2018
• 2018-01-23Watts says simulating the transient test would take enormous time, so hardware is easier; the harmonic-reduction change was not RF noise, and repeated tests are building evidence it is audible. Head-Fi, Jan 2018
• 2018-02-15Watts says a reviewer got facts wrong and published measurements bearing no similarity to his own APx555 measurements. needs context Head-Fi, Feb 2018
• 2018-02-17Watts shares Hugo 2 measurement slides from his CanJam NYC talk, explaining low output impedance, load-independent distortion, no measurable noise floor modulation or jitter, and APx555 methods. Head-Fi, Feb 2018
• 2018-02-23Watts says two-thirds of FPGA effort is testing and simulation, and that his biggest problem was inefficient use of memory blocks, not timing closure. MajorHiFi 18:23
• 2018-03-03Watts says he is building a direct measurement of transient error to prove the WTA approach, and WTA 2 is always needed to further reconstruct the 768 kHz signal. Head-Fi, Mar 2018
• 2018-03-26Watts says channel separation figures matter less than crosstalk distortion, which he tested on Hugo 2 as a check of PSU-induced distortion; DAVE's low PSU impedance avoids it. Head-Fi, Mar 2018
• 2018-04-04Watts says 1980s design was arduous: his thick film hybrid audio op-amps (0.5 GHz gain-bandwidth) took months of hand calculation, work SPICE modeling now does in a day. article, Apr 2018
• 2018-04-04Watts says 90% of Hugo 2's technology came from DAVE through reusable Verilog modules that are simulated, verified and listened to, giving Hugo 2 identical digital internal performance. article, Apr 2018
• 2018-04-28Watts says copper oxide is diodic and oxides on metal contacts add small-signal non-linearity, which he has measured as distortion from dirty contacts using 8 ohm loads. Head-Fi, Apr 2018
• 2018-04-30Watts says the SYS2722 cannot measure Dave (-118dB versus -128dB on an APx555), calls NFM a top-3 SQ indicator, and uses Verilog simulation to verify -350dB and -300.99dB performance. Head-Fi, Apr 2018
• 2018-05-13Watts posts his Munich TT2 presentation: larger FPGA, a noise shaper 100 times better than Hugo 2's, supercap PSU, output stage from the power pulse array project, measurements. Head-Fi, May 2018
• 2018-05-17Watts says he finished TT2's output stage optimization for production, measuring 0.000195% THD at 20Hz unchanged with an 8 ohm load at 12W. Head-Fi, May 2018
• 2018-05-22Watts says Dave's negative output uses an op-amp for power amps only, while TT2's uses its high-power discrete stage for speakers and headphones, and suggests XLR-terminated headphone cables. Head-Fi, May 2018
• 2018-05-27Watts says Stereophile's AP cannot measure Dave because ADC noise floor modulation interferes; the APx555 uses a notched second ADC for residuals, showing Dave's noise floor near -180dB. Head-Fi, May 2018
• 2018-06-15Watts reports a Hugo 2 battery under 0.25A load measured 670nV whether connected or not, versus about 60uV for a quality linear regulator. Head-Fi, Jun 2018
• 2018-09-03Watts says TT2 outperforms Class AB, showing no crossover distortion at 12W into 8 ohms thanks to its second-order analog noise shaper, and likens Chord's Etude feedforward amp. Head-Fi, Sep 2018
• 2018-09-26Watts shares Verilog simulation plots of his 768 kHz decimation filter with aliasing below -250 dB and 250 dB rejection at FS/2, versus -6 dB for half-band filters. Head-Fi, Sep 2018
• 2018-10-27Watts says 10 versus 20 pulse array elements helps Dave's transparency, and his noise-shaped volume control is not bit perfect but passes a -301 dB test. Head-Fi, Oct 2018
• 2018-11-22Watts jokes that a claim resembles fanciful dynamic range measurements some companies publish, as if the measuring gear were switched off too. Head-Fi, Nov 2018
• 2018-12-12Watts shows DAVE's noise floor at minus 179 dB with or without signal, zero measurable though not zero NFM; a good conventional DAC goes from minus 160 to 140 dB. Pursuit Perfect System 18:40
• 2018-12-12Watts says every circuit point has RF decoupling, with quad-layer ground planes, a digital PLL eliminates source jitter, and TT2's noise floor is minus 178 dB with zero measurable NFM. Pursuit Perfect System 34:53
• 2018-12-12Watts says it works with the M Scaler, calls the measurements state of the art (only DAVE beats them), and gives the jitter-test floor as minus 170 dB, not 178. Pursuit Perfect System 40:30
• 2018-12-12Watts says the jitter test shows no jitter components, removing source and internal jitter, and that he signs off no design until it shows no measurable noise floor modulation. Pursuit Perfect System 41:18
• 2018-12-12Watts says with a 20 hertz signal, higher-order harmonics vanish by 3 kHz on DAVE and his other DACs, at 12 W into 8 ohms balanced, unlike other power amplifiers. Pursuit Perfect System 42:02
• 2019-01-09Watts gives TT2 distortion figures, 0.042 ohm output impedance and low-gain voltages, notes no distortion above 3 kHz at 12 W, and says the FPGA sits die-down on the chassis. Head-Fi, Jan 2019
• 2019-01-20Watts details WTA1 modes, WTA2 versus the three-stage IIR, the HF filter at about -1dB at 20kHz, and says Stereophile's Qutest frequency response was wrong due to latency. Head-Fi, Jan 2019
• 2019-03-18Watts explains TT2's output amplifier as a second-order analog noise shaper replacing a nested feedback loop, giving huge HF gain and no distortion above 3 kHz. Head-Fi, Mar 2019
• 2019-04-30Watts says he has never seen packet noise contamination, measuring Hugo 2 down to -180dB, and it would not show zero measured jitter if it were sensitive to it. Head-Fi, Apr 2019
• 2019-05-11Watts says chip DACs suffer substrate noise, NFM and jitter, while his discrete DACs measure -120dB signals to +/-0.001 dB and resolve -186 dB within 1dB. Head-Fi, May 2019
• 2019-05-15Watts says Mojo is not jitter sensitive; apparent sensitivity depends on test equipment, and an APx555 shows no jitter errors. Head-Fi, May 2019
• 2019-07-17Watts says a DX output is dual AES plus volume data, then argues listening judgements and measurements both need great care, saying only the APx555 measures noise floor modulation accurately. Head-Fi, Jul 2019
• 2019-08-22Watts says setting a Pilot Pro 2 to 12 V limits peak output only above +7 dB, with no change in THD and noise, though tests of the filter show differences better. needs context Head-Fi, Aug 2019
• 2019-10-25Watts says a bit error is heard as a click, hours of SPDIF tests on his APx555 show none, and a checksum cannot guarantee accuracy. Head-Fi, Oct 2019
• 2019-12-06Watts says TID and SID are non-issues with digital sources, and explains the analog noise shaper amp eliminates crossover distortion, citing TT2 and DAVE plots and gain bandwidth figures. Head-Fi, Dec 2019
• 2019-12-16Watts describes Verilog simulation of his noise shaper as exact hardware behavior analyzed by FFT; 1 ms of output once took all day, now 50 ms takes half an hour. Passion for Sound 9:37
• 2019-12-16Watts says he can now run four million point FFTs or larger to analyze the output. Passion for Sound 10:25
• 2019-12-16Watts explains that an FFT, a fast Fourier transform, converts a signal into frequency bins to produce distortion plots showing the fundamental, noise floor and harmonics. Passion for Sound 10:36
• 2019-12-19Watts says standard measurements use steady-state signals without transients, so reconstruction accuracy only matters when transients are involved. Passion for Sound 20:54
• 2020-01-02Watts says noise floor modulation tests need identical settings with only the level reduced, and his plots show no measured modulation in any product from Mojo to DAVE. Passion for Sound 10:05
• 2020-01-10Watts advises against adding a USB-to-optical stage, saying reported gains are RF brightness mistaken for transparency, and a Dell laptop worsened his APx555 THD and noise by about 2dB. Head-Fi, Jan 2020
• 2020-01-11Watts says USB only controls his APx555, advises staying at DSD64 rather than re-modulating to higher rates before M scaler and DAVE, and praises the M scaler's DSD filter. Head-Fi, Jan 2020
• 2020-02-11Watts says bit errors show at once as a raised noise floor in averaged FFTs and are easy to hear, so they are no practical issue for USB or SPDIF. Head-Fi, Feb 2020
• 2020-04-11Watts says Hugo 2 is class A into 300 ohms, TT2 is biased an order higher with 30nS transistors, and TT2 shows no crossover or HF distortion at 12W. Head-Fi, Apr 2020
• 2020-05-06Watts says USB bit errors are rare and obvious, Hugo 2 and Mojo need at least 6.5v and 8v for best output, and non-original battery swaps risk fire. Head-Fi, May 2020
• 2020-05-06Watts says he has no wideband FFT plot of TT2 as requested, but recalls Jude publishing TT2 out-of-band noise on the measurement thread. Head-Fi, May 2020
• 2020-05-11Watts says 16FS and 256FS filters measure identically; Hugo 2's HF filter is about -1dB at 20kHz, but its warmer sound comes from less out-of-band noise and noise floor modulation. Head-Fi, May 2020
• 2020-06-25Watts says an inner amplifier linearizes the output stage inside one global feedback loop; TT2 plots show no distortion above 3 kHz for 20 Hz, 12 watts into 8 ohms. Part-Time Audiophile 20:05
• 2020-06-25Watts says his semiconductor background made him value measurements as one way to assess transparency, and his first prototype reached about -130 dB, comparable to the best DACs. Part-Time Audiophile 33:21
• 2020-06-25Watts says successive prototypes improved slightly until a breakthrough cut distortion 30 dB, from -130 to -160 dB on higher order harmonics, without expecting a sound change. Part-Time Audiophile 34:05
• 2020-06-25Watts says high order harmonics are generally the tenth harmonic and above. Part-Time Audiophile 38:21
• 2020-06-25Watts corrects the example: against a 1 kHz signal, 11 kHz is the tenth-order product, so a 200 kHz component is the 200th harmonic, inaudible on paper. Part-Time Audiophile 38:37
• 2020-07-23Watts says TT2 is not Class D, which would destroy transient timing; its single amplifier has one global feedback path, a second-order analog noise shaper and fast discrete transistors. Head-Fi, Jul 2020
• 2020-09-30Watts says his DACs use switching regulators, which sounded better than linear ones from Hugo onward, and that random RF noise, not fixed switching noise, causes noise floor modulation. Head-Fi, Sep 2020
• 2020-11-22Watts says his 0dBFS white noise test shows no out-of-band images from Hugo 2, whose digital filtering extends to 104MHz; noise up to 250kHz comes from the AP's ADC. Head-Fi, Nov 2020
• 2020-11-23Watts compares Hugo 2's out-of-band noise with the APx555's 192kHz DAC, explains the 104MHz noise shaper hump, and why gentle analog filtering needs only 4 passive components. Head-Fi, Nov 2020
• 2020-11-24Watts says DSD256 modulator noise is around -30dB at 500kHz against -130dB for Hugo 2, and that his plots differ because he uses 0dBFS white noise, not swept sine. Head-Fi, Nov 2020
• 2021-03-04Watts says residual noise at 50mV output, taken from the presentation, is 2.6uV A-weighted, which is 85.7dB below 50mV. needs context Head-Fi, Mar 2021
• 2021-03-15Watts says quick measurements on non-APx555 gear reveal little, measurements matter but interpretation is paramount, and chip DACs fail on brick-wall response, small-signal accuracy and noise floor modulation. Head-Fi, Mar 2021
• 2021-07-23Watts says the volume control output is aggressively noise shaped, not truncated or dithered, reproducing -301dB within +/-0.001 dB, and shows the M scaler truncator's -390dB noise floor. Head-Fi, Jul 2021
• 2021-07-24Watts says resolution means resolving small signals, not fixed noise (21.3 bits for Dave); Dave resolves -186dB; and 1M taps' 16.7-bit accuracy now looks insufficient for transients. Head-Fi, Jul 2021
• 2021-07-25Watts describes his -301.03dBFS FFT test requiring +/-0.001dB and +/-0.001 degree accuracy, saying phase that varies with amplitude degrades depth while constant phase shift does not. Head-Fi, Jul 2021
• 2021-08-30Watts asks where the APx 555 plots showing better performance are. needs context Head-Fi, Aug 2021
• 2021-08-31Watts says Stereophile's poor Dave -90.31dB result did not reproduce on his APx555, calls the SYS2722 inadequate, and shows Dave with zero measurable noise floor modulation and jitter. Head-Fi, Aug 2021
• 2021-10-03Watts says specific test frequencies reveal images as aliasing tones, consistent with the stop-band plus analog filter performance. needs context Head-Fi, Oct 2021
• 2021-11-09Watts says the cited plots were not made on an APx555 and shows a 2.5 V versus no-output overlay with the noise floor at -176 dB, independent of signal. Head-Fi, Nov 2021
• 2021-11-09Watts says the poster's plots are not noise floor modulation tests, which overlay 0 dBFS and -999 dBFS with identical APx555 settings; only the APx555's quad ADC can do this. Head-Fi, Nov 2021
• 2021-11-30Watts says correct filter timing errors are amplitude independent but transients intermodulate through non-sinc windows; a WTA simulation matched 0dBFS and -301dB, and coefficient accuracy improved depth. Head-Fi, Nov 2021
• 2022-01-31Watts says noise floor modulation impairs instrument separation and timbre; his DACs including Mojo 2 and Mojo show none measurably, unlike all others; the third factor is transients. Darko.Audio 8:26
• 2022-01-31Watts says depth improved at each noise shaper step, 220 dB, 240 dB, up to DAVE's 350 dB, even 330 to 350; noise shapers shrink his -301 dB test signal. Darko.Audio 22:09
• 2022-01-31Watts says DSP filters give small signals a different phase; his formal test compares phase at 0 dB and -301 dB, and 0.002 of a degree audibly suppresses depth. Darko.Audio 25:21
• 2022-01-31Watts says the DSP then showed zero phase shift at -301 dB, and it sounded better once the noise shapers were in. Darko.Audio 27:50
• 2022-01-31Watts says measuring with an ADC directly is useless because its noise floor modulation exceeds his DACs'; the APx555 instead notches the signal, limited to a single tone. Head-Fi, Jan 2022
• 2022-02-01Watts says it reproduces -301dB but its -320dB noise floor at 6kHz prevents proving 0.001dB accuracy; the 4-element noise shaper is 250dB versus DAVE's 350dB. Head-Fi, Feb 2022
• 2022-02-03Watts says peak filters are defined by Q but shelf filters are not, and shares AP plots referenced to 0dB at 1kHz. Head-Fi, Feb 2022
• 2022-02-08Watts says 14 years consulting for semiconductor firms taught right-first-time design; finished designs are frozen so a 2015 DAVE sounds like a 2022 one, and he avoids sales-driven upgrades. Head-Fi, Feb 2022
• 2022-02-18Watts says a poster's per-filter numbers match his plots, notes that summing magnitudes ignores phase, and plans to check on his APx555 with Mojo 2. needs context Head-Fi, Feb 2022
• 2022-03-14Watts says ADCs have large NFM, so measuring it needs a distortion-free analog notch before the ADC, as the APx555 does; Stereophile's measurements do not do this. Head-Fi, Mar 2022
• 2022-03-19Watts says simulation showed no difference between the settings at -90 or -120 dB, but at -301 dB amplitude was perfect while small-signal delay differed. MFG Audio Reviews 32:19
• 2022-03-19Watts says the digital simulation is the real output, and shows the DSP reproducing -301 dB within thousandths of a dB and thousandths of a degree. MFG Audio Reviews 38:18
• 2022-03-19Watts says the test used +9 dB at 20 Hz, -9 dB at 20 kHz and a 6 kHz sine; volume now spans -108 to +18 dB for sensitive IEMs. MFG Audio Reviews 39:06
• 2022-03-19Watts gives measurements: 125 dB dynamic range and distortion much as on Mojo, but 118 dB stereo separation from better supply isolation, so the battery is isolated when running permanently. MFG Audio Reviews 44:22
• 2022-03-19Watts shows no noise floor modulation (same -177 dB floor with signal on or off), low distortion, and a perfectly reproduced 16-bit small signal with left and right superimposed. MFG Audio Reviews 45:02
• 2022-03-19Watts says the ringing is expected, the 16-bit result is state of the art with only TT2 and DAVE slightly better, and Mojo sold in large numbers after 2015. MFG Audio Reviews 45:45
• 2022-03-19Watts says his A-B tests now target a measurable digital-domain error such as -301 dB phase shift, reducing it until no difference is heard, which yields incredibly small numbers. MFG Audio Reviews 49:42
• 2022-03-22Watts says digital-domain measurements reveal audible things; differences he heard were not analog-measurable but showed up in simulation or captured digital data. article, Mar 2022
• 2022-04-07Watts says M scaler depth gains led him to test phase shift with amplitude (2uS, 100nS, 10nS errors), so modules must now pass -301 dB in amplitude and phase. Head-Fi, Apr 2022
• 2022-04-08Watts says -301 dB phase measurements are digital-domain only, analog paths suffer small-signal non-linearities, and he recommends multiple 0.6mm solid-core PTFE silver-plated conductors for speaker cables and 0.4mm for interconnects. Head-Fi, Apr 2022
• 2022-04-13Watts describes his -301 dB Verilog simulation test with an 80 bit 768 kHz source, explains not publishing, and ties poor reproduced depth to small signal accuracy. Head-Fi, Apr 2022
• 2022-04-14Watts explains Verilog module simulation, says improving Dave's noise shapers from 200dB to 350 dB improved depth each step, and treats the -301 dB test as his transparency metric. Head-Fi, Apr 2022
• 2022-04-15Watts says he embeds listening options in the FPGA behind bit switches; simulation suits steady-state errors, not transients, and analog changes need SPICE and slow layouts. Head-Fi, Apr 2022
• 2022-04-16Watts says SPICE models non-linearities well below -200dB and parasitic LRC, and recalls months designing 1980s hybrid op-amps that SPICE would now do in a day. Head-Fi, Apr 2022
• 2022-04-19Watts explains wiring an RCA output into an amp's XLR input for grounded versus balanced inputs, then describes SPICE modeling of active parts, passive parts and PCB tracks. Head-Fi, Apr 2022
• 2022-05-28Watts attributes a 1 kHz measurement artifact to APx555 ground currents over USB, discusses ground loops and optical as reference, and gives settings for noise floor modulation tests. Head-Fi, May 2022
• 2022-07-25Watts recounts DAVE's nearly 3-year development, questions Stereophile's 16-bit measurements, cites -127dB A-weighted, calls SINAD worthless, and says filters must reconstruct transient timing. Head-Fi, Jul 2022
• 2022-08-19Watts says correlating error levels from digital simulation with sound quality shows that very small errors that could never be measured are perceptible, showing how sensitive hearing is. AVstore 24:23
• 2022-08-19Watts says Chord DACs' digital phase lock loop eliminates source jitter; in a test with 2 microseconds of jitter at 1 kHz he saw a noise floor of, he thinks, -170 dB and no sidebands. AVstore 38:19
• 2022-08-19Watts says DAVE measures slightly better with the M Scaler, with slightly lower distortion and noise and no jitter difference, because DAVE's WTA filter does no work and 80 percent of the chip sits idle. AVstore 39:21
• 2022-08-19Watts says that generates less ground-plane noise, making it slightly easier for the DAC, a very small difference just detectable in measurements. needs context AVstore 40:05
• 2022-08-25Watts says claiming no impulse-response difference while noting TT2's sharp filter is contradictory, since impulse and frequency responses are FFT equivalents and a sharp filter needs a long impulse response. Head-Fi, Aug 2022
• 2022-08-26Watts explains TT2's balanced output (gain 5 and -1 amps), says single-ended is more transparent owing to fewer feedback parts, shows measurements, and says the pulse array is his IP. Head-Fi, Aug 2022
• 2022-09-06Watts says measurements correlate weakly with listening and depend on intent, his published results represent production DAVEs, and buyers should listen at home before purchasing. Head-Fi, Sep 2022
• 2022-09-07Watts says unidentified blind tests kill sensitivity, DAVE has no measurable noise floor modulation, and explains setting up the AP test correctly with -999dB and fixed input levels. Head-Fi, Sep 2022
• 2022-09-18Watts says Dan solves problems that affect sound; his distortion is extraordinary, quoted as 0.0007 % at 80 dB at 1 kilohertz, unbelievably small for a headphone. The Source AV 36:43
• 2023-01-18Watts says the 192k output for Audio Precision measurements uses pseudo-Gaussian dither, noisier than triangular or rectangular dither but sounding closer to the noise-shaped 768k output. Head-Fi, Jan 2023
• 2023-02-04Watts says 1990s DACs showed 1 or 2 dB of error at -100 dB; the pulse array eliminated it, and -120 dB measures accurate within a thousandth of a dB. Dusty Audio 19:20
• 2023-02-04Watts says such measurements take three or four hours, that better small-signal accuracy gave better detail and depth, and that reproduced depth collapses compared with a distant cathedral organ. Dusty Audio 20:06
• 2023-02-04Watts says noise shaper performance is measured by digital simulation; for Hugo he worked to 200 dB (32-bit accuracy), while chip makers generally work to 140 dB. Dusty Audio 21:41
• 2023-02-04Watts says conventional DACs measure about a -160 dB noise floor with a -60 dB signal but the noise rises with signal level; the aim is a static noise floor. Dusty Audio 31:39
• 2023-02-04Watts says noise floor changes at -350 dB still impair instrument separation and timbre; they show only in digital simulation, never with real test equipment, yet remain audible. Dusty Audio 34:43
• 2023-02-04Watts says he verifies bit perfection by measurement: after each FPGA place and route he ran optical into an Audio Precision for hours of averaged FFTs. Dusty Audio 1:09:04
• 2023-02-04Watts says Xilinx tools six or seven years ago were poor and each place and route sounded different; today's tools are good, but he still runs the test. Dusty Audio 1:09:54
• 2023-02-04Watts says if one bit falls out the measurement shows a huge, easily seen error. Dusty Audio 1:10:39
• 2023-02-05Watts says 8 watts dissipated from a 1 V core creates much more circuit noise, so linears magnify digital core noise; he has recently been doing SPICE modeling. Soundnews 27:55
• 2023-02-05Watts describes SPICE as modeling software with parameters for transistors and resistors, including parasitic inductance and capacitance. Soundnews 28:41
• 2023-02-05Watts says SPICE lets him fully analyze filters and switching stages before building, measuring at picovolts or attovolts, and he has used it to improve RF filters. Soundnews 29:02
• 2023-02-05Watts says a car battery has no RF noise, 300 amps of delivery and under one milliohm impedance, measuring like a short on the Audio Precision: the reference supply. Soundnews 38:19
• 2023-02-05Watts says the difference is tiny; of many TT2 supplies measured at 100 kHz bandwidth all degraded performance except one, at half a dB, which sounded like a car battery. Soundnews 41:34
• 2023-02-05Watts says after six years his digital PLL matched the buffer's ideal behavior; injecting 2 microseconds of 1 kHz jitter produces no output sidebands, measured down to -160 dB. Soundnews 47:29
• 2023-02-06Watts says SPICE is accurate only with good parameter data, unlike 100% accurate Verilog, and parasitics in high gain-bandwidth discrete circuits make op-amps the safer choice. Head-Fi, Feb 2023
• 2023-02-20Watts says Mojo 2's 4-element pulse array runs its noise shaper slower for low distortion, so noise rises around 100k and falls at 400k from analog filtering. Head-Fi, Feb 2023
• 2023-03-18Watts says TT2 has higher distortion than Dave, that third-party Dave measurements fall far short of his own, and quotes Hi-Fi News measuring 0.000007% THD at 1kHz. Head-Fi, Mar 2023
• 2023-03-19Watts shares a 16-bit -90.3dB undithered test of the returned Stereophile Dave, points to PWM DAC slides, and says measurements show how bad, not how good, something sounds. Head-Fi, Mar 2023
• 2023-03-19Watts says phase shift with amplitude, found after the M scaler work, affects depth; tuning Mojo's noise shaper for minimal -301dB phase error led to Mojo 2's UHD DSP. Head-Fi, Mar 2023
• 2023-03-26Watts says SPICE simulations of his RF filters show a switching waveform is easily reduced to nanovolts with a couple of filter stages like those in his DACs. Eric's Hi-Fi 15:47
• 2023-03-26Watts identifies the measurements in question as the ASR reviews. Eric's Hi-Fi 24:01
• 2023-03-26Watts says M Scaler output jitter is irrelevant because his DACs eliminate it; it was never designed for low jitter, and 2 microseconds of jitter has no measured impact. Eric's Hi-Fi 24:19
• 2023-03-26Watts says M Scaler jitter is nanoseconds, so that criticism is irrelevant; DAVE measured extraordinarily for him and HiFi News, recalled as 0.0000 four or five zero seven percent distortion. Eric's Hi-Fi 25:05
• 2023-03-26Watts says DAVE measures better than any DAC he has seen, yet others using an APx555 differ; one manufacturer's terrible TT2 and M Scaler results came from ground loops. Eric's Hi-Fi 25:47
• 2023-03-26Watts says the manufacturer rebuilt his lab and it then measured perfectly; the APx555 is very sensitive to grounding and laptops, so he sets his lab up carefully. Eric's Hi-Fi 26:36
• 2023-03-26Watts says he makes the APx555 work correctly with the DAC rather than optimizing for it, publishes honest measurements, and finds differing review numbers troubling. Eric's Hi-Fi 27:20
• 2023-03-26Watts says differing third-party measurements imply he is lying about his own, which he does not do. Eric's Hi-Fi 28:14
• 2023-03-26Watts says he hears -350 dB errors found in digital simulation that analog test gear cannot measure, and claims no measurable noise floor modulation in any of his DACs. Eric's Hi-Fi 31:00
• 2023-03-28Watts says he targets 24-bit performance with harmonics below -144 dB, and out-of-band distortion at 250 kHz proved audible when he reduced it. The Headphone Show 41:40
• 2023-03-28Watts says reproduced depth falls far short of live, small-signal nonlinearity is crucial, and all his digital parts are tested in simulation with a -301 dB signal. The Headphone Show 42:34
• 2023-03-28Watts says simulating transients at 10 nanoseconds shows no change in transient performance, so the DSD small-signal transient problem is absent. needs context The Headphone Show 48:07
• 2023-03-28Watts says he simulates digital circuits in Verilog with the Xilinx tools' behavioral simulator, matching hardware, and uses SPICE, MATLAB and Excel models, though four million Excel points is painful. The Headphone Show 51:29
• 2023-04-03Watts says every module must pass a -301 dB test within 0.001 dB amplitude accuracy, and every module that failed a listening test had failed the -301 dB test. Amplify Audio 6:28
• 2023-06-01Watts says a PowerAdd power bank and the supplied SMPS sounded and measured the same in the audio band, while other SMPS tested for TT2 measured poorly at high bandwidth. Head-Fi, Jun 2023
• 2023-06-02Watts says the filters together with the supercaps filter from 5 Hz to GHz with no switching-frequency notches, and the mains-connected APx555 suffers from mains and earthing noise loops. Head-Fi, Jun 2023
• 2023-08-28Watts says he still lacks metalwork and PCBs for an unnamed project, though coding is nearly done with one of the last modules passing simulation. needs context Head-Fi, Aug 2023
• 2023-09-23Watts describes his cycle of FPGA design, simulation, digital measurement and AB listening tests, and says he has more things to try on the new scaler. Head-Fi, Sep 2023
• 2023-10-01Watts says digital simulation shows errors down to -400 dB before a listening test, and when such a tiny change is audible he asks whether it is placebo. The Source AV 34:06
• 2023-12-04Watts says Stereophile's Dave response curves are wrong, likely ignoring latency, and that its 384k response reflects the filters from 16FS to 104M and analog filtering. Head-Fi, Dec 2023
• 2024-03-20Watts says noise floor modulation hundreds of dB down is audible, shown by simulating errors digitally and listening, which is why cables can change brightness with zero measurable difference. MFG Audio Reviews 15:45
• 2024-03-20Watts says signal-dependent ripple feeds through power amplifiers, visible as ripple harmonics in Stereophile measurements, audibly softening bass definition; regulated linear supplies still pass significant ripple. MFG Audio Reviews 33:04
• 2024-03-20Watts says switch mode supplies always have input and output RF filters for EMC, fixed-frequency switching matters little, and during COVID he SPICE-modeled filters for noise up to 10 GHz. MFG Audio Reviews 33:55
• 2024-03-20Watts says his SPICE models included parasitics; a two-stage LC filter cut fixed-frequency switching noise to picovolts, but random noise up to 10 GHz needed very complex filtering. MFG Audio Reviews 34:50
• 2024-03-20Watts says he measures designs digitally down to -400 dB by FFT and listens as errors are removed; while developing DAVE his noise shapers performed at 200 dB. MFG Audio Reviews 43:16
• 2024-05-10Watts says 'the key is random' and that he ran a SPICE simulation in which he modeled capacitors. Reactcore 39
• 2024-05-10Watts says the simulation started with one volt of random RF noise up to 10 gigahertz, where noise is a problem, and led to the very complex RF filters. Reactcore 51
• 2024-06-18Watts says Quartet will cost more than DAVE, and describes Spice-modeled 'pinch-off' RF filters in its separate supply and input, isolating DAVE from its noise and making the sound warmer and smoother. article, Jun 2024
• 2024-06-25Watts says iFi's 1uV PSU noise figure is meaningless without FFT bandwidth, implying 141 uV broadband; TT2's noise floor is 9nV and Chord's Li-ion batteries measure below the APx555. Head-Fi, Jun 2024
• 2024-07-12Watts says simulation lets him measure digital circuits at minus 350 dB distortion and below, and his DACs' digital circuits must reproduce minus 301 dB perfectly. HIFICLUB 18:45
• 2024-09-29Watts says his son wrote an FFT algorithm from first principles; at a thousand-digit resolution distortion and noise were at 3,500 dB, proving the tool and computation correct. The Source AV 7:12
• 2024-09-29Watts says his son, a Tonmeister student at Surrey on a recording-studio placement in Belgium, built the tool in weeks, removing the 300 dB limit of Windows 64-bit floating point. The Source AV 8:10
• 2024-09-29Watts says running the coefficients through the new tool showed results nothing like expected because his coefficient tools were flawed, so he changed the tool set for much better precision. The Source AV 8:53
• 2024-09-29Watts says Chord has asked why he is late; new maths and measurement tools revealed something new and gave better sound, probably an incremental rather than night-and-day change. The Source AV 20:03
• 2024-10-02Watts says a new unlimited-precision FFT showed his old coefficients were wrong; corrected ones kept the same preferred settings, improved sound, and delayed everything 3 months. Head-Fi, Oct 2024
• 2025-01-09Watts describes a transient reconstruction test giving the M Scaler 22-bit accuracy but says raw numbers miss perception, and rejects an extra amp since DAVE drives Stealth to ear-damaging levels. Head-Fi, Jan 2025
• 2025-01-13Watts compares feed-forward correction (about 20dB) with his second-order analog noise shaper (90dB), showing TT2 into 8 ohms, and links crossover distortion to amplitude-dependent transient delay. Head-Fi, Jan 2025
• 2025-01-13Watts lists the reference supply, pulse array flip-flops, gain stage and output stage as distortion sources, and says a 20Hz 12W TT2 test shows crossover distortion eliminated. Head-Fi, Jan 2025
• 2025-02-17Watts says 64-bit float on a PC is not accurate enough for IIR work; his -301 dB test needs amplitude within a thousandth of a dB and phase within a thousandth of a degree. audio-2G 17:33
• 2025-03-25Watts argues comparing DAC output with original sampled data is pointless since an ideal DAC reconstructs the original signal, and says his son Daniel is building the pro ADC project. Head-Fi, Mar 2025
• 2026-03-17Watts says information below the 16-bit level is encoded by dither or noise shaping, so 16-bit has 96 dB SNR yet an Audio Precision analyzer passes a -130 dB signal. ecoustics 7:02
• 2026-03-17Watts says the errors cannot be measured; every digital module he develops must reproduce a -301 dB test signal within one thousandth of a dB. ecoustics 41:24
• 2026-03-17Watts says small-signal phase must be within one thousandth of a degree of the 0 dB phase, harder than the amplitude test, and failing it audibly loses depth. ecoustics 42:36
• 2026-05-03Watts says measurements matter for finding the size of an error, using advanced mathematical tools, but what counts is whether the error has audible consequences. Audio Force 4:28
• 2026-05-03Watts says FPGA simulation can show an error at say minus 300 dB, then listening reveals whether reducing it matters; listening is far more important than measurements. Audio Force 5:12
• 2026-10-02Watts says NFM shows when the signal is switched on and off at fixed gain, Audio Precision autoscaling off; high-performance DACs show 2 to 3 dB. HiFi Buys 53:19
• 2026-10-02Watts says he would code, simulate, measure digitally and listen; each step from 220 to 240 to 260 dB gave better depth, ending at 330, then 350 dB. HiFi Buys 1:21:26
• 2026-10-02Watts says every module must reproduce a -301 dB signal within a thousandth of a dB or depth suffers; in 2017 he took Blu 2 from 0.5M to 1M taps. HiFi Buys 1:24:04
• 2026-10-02Watts says he picked the best-sounding setting, then simulations showed it had much better phase timing accuracy at -301 dB. HiFi Buys 1:29:18
• 2026-10-02Watts says modern pulse array DACs measure perfectly, a -120 dB signal within a thousandth of a dB, yet ultra-small errors still matter profoundly for depth. HiFi Buys 1:39:33
• 2026-10-02Watts says an impulse has full energy at half FS, so it is an illegal signal for testing, though useful because it shows the filter's coefficients exactly. HiFi Buys 1:51:31
• 2026-10-02Watts says music must be band-limited to be reconstructed properly, and an illegal Dirac impulse is valuable because it shows exactly what a single-stage filter does. HiFi Buys 1:54:34
• 2026-10-02Watts says a long filter with heavy pre- and post-ringing followed by a notch filter would show no ringing and look perfect, so impulse plots can catch people out. HiFi Buys 1:55:08
• 2026-10-11Watts says Quartet took longer because his son Daniel built unlimited-precision coefficient tools; a test sine computed to 3,000 decimal places showed distortion and noise about 3 thousand dB down. Distorsiuni Interioare 8:25
• 2026-10-17Watts says the EQ at extreme settings passes a minus 301 dB test, phase within a thousandth of a degree and level within a thousandth of a dB, so it is transparent. article, Oct 2026