Choosing and comparing inputs

Inputs, sources, cables and clocking

Answers on this topic

Everything he said on this topic (201)

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

2014-04-01Watts says Hugo decodes DoP after input selection, and its FPGA SPDIF receiver should run at 384 kHz, untested on hardware, allowing DSD128 over coax once sources exist. Head-Fi, Apr 2014
2014-04-16Watts says he prefers optical as smoother and more natural; it has more jitter than coax, which his DACs remove, but reduces ground-induced RF noise and noise floor modulation. Head-Fi, Apr 2014
2014-04-17Watts relays Chord's Matt that aptX is much better than standard Bluetooth, which sounds noisy because of its low data rates. Head-Fi, Apr 2014
2014-05-13Watts says Hugo's USB chip takes timing from the FPGA, but the DPLL makes that minor; input differences come from RF noise causing noise floor modulation, so he prefers optical. Head-Fi, May 2014
2014-06-22Watts re-tests optical vs coax on Hugo, finds optical warmer with better separation, and explains how RF-induced noise floor modulation harms separation and timbre. Head-Fi, Jun 2014
2014-06-24Watts says Hugo's SD USB input loses no performance despite not being isochronous, because Hugo's jitter elimination works, and his isolator has arrived. Head-Fi, Jun 2014
2014-09-30Watts advises using USB over optical rather than letting the PC resample, and says decimating 88.2 to 44.1 is easier than upsampling as decimation has no timing problems. Head-Fi, Sep 2014
2014-10-01Watts says the Olimex breaks Hugo's HD USB negotiation but makes the SD input smoother, and suspects it uses the Analog Devices isolator chip with 2pF coupling. Head-Fi, Oct 2014
2014-10-08Watts discusses Hugo's low fatigue and prototype surprise, says the source matters little via optical, hears no plastic vs glass difference, and mentions Chord projects nearly ready. Head-Fi, Oct 2014
2014-10-26Watts says the Olimex isolator works only with the SD USB input, not at all on the HD USB input, and only up to 48 kHz. Head-Fi, Oct 2014
2014-10-27Watts notes optical runs only to 192 kHz, some transmitters to 96 kHz, and says low-power mobile sources suffer far less from the noise problem than PCs. Head-Fi, Oct 2014
2014-10-28Watts says USB 5V only detects a connection and powers the HD USB chip with RF decoupled, USB-to-optical converters should work, and mobile sources are already low-noise. Head-Fi, Oct 2014
2015-03-27Watts says his USB input is isochronous asynchronous: asynchronous on the USB side but synchronous inside the FPGA, whose clock sets the timing. Audiophile Style, Mar 2015
2015-04-20Watts gives each input's maximum data width and rate (SD USB and Bluetooth 16-bit/48 kHz, HD USB 32-bit/384 kHz, optical 192 kHz, coax 384 kHz) and battery life by input. Head-Fi, Apr 2015
2015-07-19Watts says optical is the best input on Hugo. Head-Fi, Jul 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
2015-11-23Watts 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
2016-02-23Watts says optical will sound best and not to worry about source jitter because Dave eliminates it. Head-Fi, Feb 2016
2016-02-24Watts says for both TT and Dave USB is best, closely followed by optical, with coax last. Head-Fi, Feb 2016
2016-02-24Watts says his DACs' DPLL removes incoming jitter, so optical's benefit is galvanic isolation reducing noise floor modulation, while USB is also isolated and already clocked by the DAC. Head-Fi, Feb 2016
2016-03-22Watts agrees USB is a tad more detailed than optical, with optical showing barely measurable jitter degradation, because USB timing comes from the FPGA; both are galvanically isolated. Head-Fi, Mar 2016
2016-03-31Watts suggests the files are likely not bit perfect, since one gain-scaling stage loses depth and bad truncation hardens sound; a non-bit-perfect optical link would cause dropouts instead. needs context Head-Fi, Mar 2016
2016-04-10Watts says I2S is not supported as an input on DAVE. Head-Fi, Apr 2016
2016-04-22Watts preferred a $2 USB cable over a $200 one on DAVE until he separated the headphone cable, then heard no difference; he says AES input injects RF, sounding brighter. Head-Fi, Apr 2016
2016-04-25Watts says optical handles 24/192 only with a good transmitter and cable, needing glass fiber for longer runs, and that his FPGA compensates the receiver's rise and fall time mismatch. Head-Fi, Apr 2016
2016-06-22Watts says the unit sounds like it needs service, and that optical at 192k needs a low-loss cable: 0.25M plastic should work, longer runs need quality glass fiber. Head-Fi, Jun 2016
2016-07-23Watts says another galvanic isolator won't help DAVE, a JitterBug gets to 99.75%, and isolated USB now edges optical in detail and flow because its clock comes from DAVE. Head-Fi, Jul 2016
2016-08-28Watts says DAVE's USB 5 V is isolated, and battery-laptop or USB-vs-optical differences are tiny; optical gives full RF isolation, USB slightly better timing from DAVE's clock. Head-Fi, Aug 2016
2016-11-19Watts says it can be done on BNC inputs but not DX outputs, without sonic benefit, as pull-ups keep unused BNC inputs inactive and their ground joins the ground plane. needs context Head-Fi, Nov 2016
2017-01-09Watts says it accepts DoP DSD64 and DSD128 but nothing higher because the SPDIF input is limited to 384 kHz. needs context Head-Fi, Jan 2017
2017-01-09Watts says the bi-directional USB port carries any rate at 32 bits each way and is galvanically isolated, as are the BNC outputs, and isolation makes the biggest difference. needs context Head-Fi, Jan 2017
2017-02-19Watts says Hugo 2 has dual coax inputs for desktop-mode convenience and dual data mode with M scalers at 768 kHz, using small jacks because two BNCs would not fit. Head-Fi, Feb 2017
2017-02-20Watts says DX is AES dual-data SPDIF with volume in user data; Mojo takes 768 only via USB, coax tops at 384 kHz, and Hugo 2 now accepts dual-data coax. Head-Fi, Feb 2017
2017-02-28Watts heard almost no optical versus USB difference on Hugo 2 with a mains laptop and headphones, crediting RF-filtered USB ground and VBUS, separate input supplies and 144 dB crosstalk. Head-Fi, Feb 2017
2017-02-28Watts says USB galvanic isolation may help when driving a power amp depending on source noise, and charging makes no measured and no reliably audible difference. Head-Fi, Feb 2017
2017-03-03Watts says USB and optical sounded and measured the same on production Hugo 2 with headphones and an MSI laptop, so owners need not worry about it. Head-Fi, Mar 2017
2017-03-04Watts explains that headphones keep source noise common mode, while a grounded power amp drives ground-loop currents through Hugo 2's ground plane, now limited by a USB RF ground filter. Head-Fi, Mar 2017
2017-03-15Watts says further isolating USB would have no effect, since optical and USB sounded the same with a high-spec laptop and headphones, though other sources may differ. Head-Fi, Mar 2017
2017-03-16Watts explains that an earthed power amp lets source currents loop through Hugo 2's ground plane, while optical, galvanic isolation or battery sources prevent this. Head-Fi, Mar 2017
2017-03-22Watts says unused inputs are powered down except the USB decoder, kept on when USB is connected because some apps crash otherwise. Head-Fi, Mar 2017
2017-03-26Watts says his laptop having both optical and USB outputs may explain the result by removing source variability, and he will look into it again. needs context Head-Fi, Mar 2017
2017-03-26Watts says this was largely already in Mojo, Hugo 2 has better PSU isolation, and he will re-run tests with Mojo, Hugo 2 and DAVE after a surprising result. needs context Head-Fi, Mar 2017
2017-03-28Watts says a link is bit perfect or obviously failing, suggests DoP DSD as a test, and says glitches usually come from the source processor. Head-Fi, Mar 2017
2017-04-09Watts says USB timing comes from the DAC, optical and USB sounded the same on headphones, and all jitter is eliminated from a measurement point of view. Head-Fi, Apr 2017
2017-04-20Watts says a mono 3.5 mm plug should connect to the COAX1 input fine. Head-Fi, Apr 2017
2017-04-20Watts says a mono 3.5 mm plug grounds coax 2, which is ideal, and confirms a poster's reading of the stereo plug wiring. Head-Fi, Apr 2017
2017-04-20Watts says unused digital inputs should ideally be shorted or left floating, which is preferable to having the signal on two inputs at once. Head-Fi, Apr 2017
2017-05-17Watts could not reliably hear optical versus USB on headphones with a mains laptop, but heard differences with a power-amp ground loop; brighter sound means more noise floor modulation. Head-Fi, May 2017
2017-06-01Watts gives the stereo 3.5 mm wiring for the coax inputs: tip is coax 1, first ring coax 2, second ring ground for both. Head-Fi, Jun 2017
2017-06-08Watts says galvanic isolation mattered greatly on Hugo 1, but Hugo 2's RF filtering and supply isolation (over 144 dB separation) cut its benefit tenfold; he suggests listening to USB versus optical to test sensitivity. Head-Fi, Jun 2017
2017-06-18Watts says with one source he could not reliably tell optical from USB on Hugo 2, though this may vary, and he usually uses optical for convenience with his PC. Head-Fi, Jun 2017
2017-07-17Watts says USB and optical sounded identical on Hugo 2 only with headphones and one MSI laptop; grounding the analog output made a difference, though the gap is greatly reduced. Head-Fi, Jul 2017
2017-08-21Watts says 32 kHz NICAM is obsolete; Hugo 2's SPDIF inputs still accept it, shown red (26 to 45.2 kHz), while USB supports only 44.1 to 768 kHz. Head-Fi, Aug 2017
2017-09-06Watts says all Hugo 2 inputs are treated the same, but the source must not up-sample, since PC-based up-samplers lack Hugo 2's processing capability. Head-Fi, Sep 2017
2017-09-27Watts says aptX HD is still lossy even at 48 kHz, at 576 kbps with 4:1 compression, and Sony LDAC is also lossy. Head-Fi, Sep 2017
2017-10-02Watts says he hears no difference between USB cables on DAVE, optical versus USB is minute, and a battery source via DAVE's isolated USB isolates better than mains-powered optical. Head-Fi, Oct 2017
2017-10-21Watts says Hugo 2's USB has full RF filtering, he heard no change with many USB cables, doubts cable ferrites matter, and heard no optical vs USB difference from a laptop. Head-Fi, Oct 2017
2017-12-02Watts says he heard no optical vs USB difference on Hugo 2 from his laptop with headphones, a small one with grounded outputs, and credits improved USB RF filtering. Head-Fi, Dec 2017
2018-01-02Watts says unused BNC inputs on DAVE are fine, as the SPDIF receiver output is fixed at zero when left floating. Head-Fi, Jan 2018
2018-01-04Watts says USB data is differential, so ground and VBUS can be isolated from common-mode RF with chip ferrites, which is why Hugo 2's USB closed the gap with optical. Head-Fi, Jan 2018
2018-01-08Watts says he heard no USB vs optical difference on Hugo 2 with a laptop and headphones, so his DPLL is sonically perfect, and the warmer source is better. Head-Fi, Jan 2018
2018-01-10Watts says get Hugo 2 for headphones as any external amp degrades transparency; with headphones USB sounded like optical, so isolation matters only with mains-powered amps. Head-Fi, Jan 2018
2018-01-11Watts now attributes USB's slight brightness on DAVE to RF through ground loops and the isolators' 2 pF, not timing, since Hugo 2 USB sounds like optical. Head-Fi, Jan 2018
2018-01-11Watts says optical is the best input; the task is getting the other inputs to match it. Head-Fi, Jan 2018
2018-01-12Watts says a battery-powered laptop via USB matches optical; USB's slight brightness is RF pick-up, not better timing, and vanishes when the laptop is unplugged from mains. Head-Fi, Jan 2018
2018-01-13Watts says conventional SPDIF receivers with analog PLLs create signal-correlated jitter, while his digital receiver and DPLL remove it and source jitter, so I2S or HDMI offers no benefit. Head-Fi, Jan 2018
2018-01-16Watts says with low-noise sources USB equals optical, while noisy sources favor optical; if they sound the same, USB is preferable as it covers all files. Head-Fi, Jan 2018
2018-02-07Watts says the M scaler treats the BNC input like any other; which input sounds best depends on source noise and system sensitivity, and he hears no difference between inputs. Head-Fi, Feb 2018
2018-02-11Watts says a standard stereo 3.5mm cable connects Hugo 2 to an M scaler; cheap non-75-ohm cables worked at 705/768 kHz because of de-glitching and rise/fall adjustment. Head-Fi, Feb 2018
2018-02-18Watts says USB is always live when Hugo 2 is powered and source selection only switches decoded data, so the PC sees no difference; he suspects coincidence. Head-Fi, Feb 2018
2018-03-20Watts says complex USB gear adds RF brightness, optical is the benchmark, and gives WTA overload margin, M scaler latency (630 ms, video mode 104 mS) and 16.6-bit accuracy. Head-Fi, Mar 2018
2018-03-27Watts says he has not heard of the reported Bluetooth problem, uses a high quality module, and suspects the source. needs context Head-Fi, Mar 2018
2018-04-07Watts says SPDIF data failures are extremely rare, would be audible and measurable, and in all-day APx555 tests he has never seen a bit failure. Head-Fi, Apr 2018
2018-04-08Watts says USB ferrites changed nothing for him; Hugo 2's 300 MHz chip ferrites made USB sound like optical on headphones, so try 300 MHz types. Head-Fi, Apr 2018
2018-04-12Watts says Toshiba stopped making its good TX179 Toslink parts; replacements have asymmetric edges, so many DACs dropped 192k optical, but his FPGA receiver compensates. Head-Fi, Apr 2018
2018-04-12Watts says DAVE and Hugo 2 run identical optical receiver code and chip, and 192k optical is marginal but works on DAVE with a quality transmitter and cable. Head-Fi, Apr 2018
2018-04-20Watts says USB is best, AES/EBU is a joke standard, and external clocks either worsen sound or do nothing because DAVE's crucial clock sits beside the pulse array. Head-Fi, Apr 2018
2018-05-04Watts says with his MSI laptop and headphones Hugo 2 sounded the same on optical and USB, a power amp reveals differences, and optical is the source benchmark. Head-Fi, May 2018
2018-05-15Watts says his DPLL creates a new word clock frequency locked to the source on the 104.25 MHz master clock, took 6 years, and made Hugo 2 USB match optical. Head-Fi, May 2018
2018-05-15Watts agrees Toslink is the gold standard and the target USB must hit, assuming the Toslink link is bit perfect, since drop-outs would be easily heard otherwise. Head-Fi, May 2018
2018-05-17Watts says all mains-powered DAC/amps have isolation, USB sounds very close to optical, he is amazed 2Qute can drive a loudspeaker, and he explains his single-stage output amplifier. Head-Fi, May 2018
2018-05-26Watts says the Chord Windows driver resends faulty USB packets unlike driverless USB, errors would sound as clicks, and optical errors are all-or-nothing and rare in practice. Head-Fi, May 2018
2018-06-09Watts explains his fast-locking PLL-free SPDIF decoder, a DPLL with adaptive time constants re-locking to a local 104.25 MHz clock, and volume ramping that makes source switching seamless. Head-Fi, Jun 2018
2018-06-11Watts says his all-digital SPDIF receiver decodes jitter up to 25% of a bit interval, adapts to optical rise and fall times, and will be reused in all new designs. Head-Fi, Jun 2018
2018-07-06Watts suggests sound differences between CD players into Qutest via optical likely come from differing error rates, or RF upsetting the headphone amp, and says rips give error-free data. Head-Fi, Jul 2018
2018-07-23Watts explains Hugo 2's dual data link (two 384k cables), says FPGA RF noise keeps the scaler separate, shows his homemade flight cable, and rates USB and optical equal. Head-Fi, Jul 2018
2018-07-29Watts says optical and USB sound the same on Hugo 2 with headphones but differ once grounded; coax lacks galvanic isolation, so RF raises noise floor modulation and sounds brighter. Head-Fi, Jul 2018
2018-07-29Watts hears no difference between battery and the supplied PSU, warns non-supplied PSUs may void warranty (never above 15V), and found laptop battery vs mains and optical vs USB identical. Head-Fi, Jul 2018
2018-07-29Watts says optical is warmer and smoother from complete galvanic isolation, USB comes close, and coax cannot take RF filtering without degrading lock. Head-Fi, Jul 2018
2018-07-29Watts says sound quality can only be impaired by RF noise through the ground, which optical avoids, and source jitter is not an issue with his DACs. Head-Fi, Jul 2018
2018-07-29Watts says optical is perfect galvanic isolation with near-zero coupling capacitance, while every electrical digital connection carries ground RF noise that isolation coupling capacitance passes at GHz frequencies. Head-Fi, Jul 2018
2018-07-30Watts says it does DSD512 on USB, 384 on coax, and 768 with dual coax. needs context Head-Fi, Jul 2018
2018-07-30Watts says a 'fuller' coax sound, if brighter, is extra noise floor modulation mistaken for transparency, and coax can give flatter, wider staging with less depth. Head-Fi, Jul 2018
2018-07-30Watts confirms a summary but notes optical has an upper limit of 192 kHz, which gives 0.25M taps. needs context Head-Fi, Jul 2018
2018-08-06Watts suggests an optical switch, saying that if optical attenuation is not a problem there will be no sound-quality loss. Head-Fi, Aug 2018
2018-08-06Watts says mirror-based optical switching should work and is cheap to try, unlike DACs with two optical inputs, which switch electrical signals internally. Head-Fi, Aug 2018
2018-08-06Watts says source results vary (YMMV); his MSI laptop's optical and USB sound the same, but that will not hold for all laptops or sources. Head-Fi, Aug 2018
2018-08-08Watts says optical cannot carry 768 kHz because Toslink transmitters and receivers are not fast enough; glass fiber itself would allow it in principle. Head-Fi, Aug 2018
2018-09-01Watts says a wider soundstage often means truncated depth from correlated source noise, which optical prevents; the better source has more warmth and deeper depth. Head-Fi, Sep 2018
2018-09-03Watts says optical either sounds the same as USB or warmer, and the challenge is making USB sound as good as optical. Head-Fi, Sep 2018
2018-09-03Watts recommends optical, warning against the RF noise of other inputs. Head-Fi, Sep 2018
2018-09-04Watts says inputs can be selected with the source switch or remote, or auto mode picks a locked SPDIF or non-silent USB input, with USB taking priority. Head-Fi, Sep 2018
2018-09-06Watts says Blu 2 uses USB VBUS only as an RF-filtered logic flag, so removing it just disables the USB input and cannot change sound quality. Head-Fi, Sep 2018
2018-09-15Watts says USB is best compared with coax or AES. needs context Head-Fi, Sep 2018
2018-10-14Watts says Hugo 2 has USB RF filtering and measured no effect from 2uS input jitter, heard no USB vs optical difference, and advises avoiding source gadgets that add RF. Head-Fi, Oct 2018
2018-11-02Watts says a bit-perfect optical source always sounds and measures the same, in his experience, on Hugo 2 or any other Chord DAC. Head-Fi, Nov 2018
2018-11-13Watts says the SPDIF input is a straight wire into the FPGA, where his receiver design decodes it before it is processed identically to the other inputs. Head-Fi, Nov 2018
2018-11-13Watts says USB is decoded and buffered by an Atmel ARM device with custom code, clocked from the FPGA's 104MHz master clock; the FPGA handles everything else. Head-Fi, Nov 2018
2018-11-26Watts says using optical requires disconnecting other sources, otherwise the isolation is shorted via the BNC ground or galvanic isolation coupling capacitance. Head-Fi, Nov 2018
2019-02-24Watts explains that noise harms sound via ground-plane current causing RF intermodulation and noise floor modulation; optical avoids it unless mains-powered sources form an electrical loop. Head-Fi, Feb 2019
2019-02-25Watts says battery power is the reference, optical and USB sound nearly identical on the M scaler, TT2 gains nothing from batteries, and 10 minutes of warm-up is needed. Head-Fi, Feb 2019
2019-03-20Watts clarifies that Hugo 2 accepts 768 kHz via USB and via the dual SPDIF coax inputs. Head-Fi, Mar 2019
2019-04-08Watts says Toslink is the reference input since it injects no RF into the ground plane, his DPLL removes source jitter, and he heard no consistent USB-optical difference. Head-Fi, Apr 2019
2019-04-19Watts says chip ferrites in the coax ground corrupted data, but USB tolerates ground ferrites as differential signaling, which is why the M Scaler is isolated on the transmit side. Head-Fi, Apr 2019
2019-05-02Watts gives the M scaler's 65 C thermal trip, says it recovers transient timing to 16-bit accuracy rather than adding information, and attributes optical's darker sound to RF, not jitter. Head-Fi, May 2019
2019-05-03Watts says AES3 and SPDIF use effectively the same data protocol, so all products will work as long as the signal goes into the optical or coax inputs. Head-Fi, May 2019
2019-07-05Watts says if it locks it is fine; optical switchers he has used work well, and an AB listening test can confirm no degradation. Head-Fi, Jul 2019
2019-07-17Watts says he has not tried to replicate a reported issue and finds it odd, since the USB word clock passes through the same DPLL modules as the SPDIF inputs. needs context Head-Fi, Jul 2019
2019-07-20Watts says Qutest, like all his DACs, decodes DoP over SPDIF, so DSD64 works over optical, which is its maximum there. Head-Fi, Jul 2019
2019-09-30Watts says Qutest's optical input runs at 192 kHz if source and fiber allow, but replacement optical parts for discontinued Toshiba devices are less reliable at 192 kHz. Head-Fi, Sep 2019
2019-10-16Watts says ground-plane currents cause noise floor modulation, battery Hugo 2 into headphones showed no optical-USB difference, and his M scaler's dual galvanic isolation makes source noise a non-issue. Head-Fi, Oct 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
2019-12-05Watts says the USB input needs source VBUS to power the decoder chip on the isolator's source side, so decoding noise cannot affect the DAC. Head-Fi, Dec 2019
2019-12-18Watts says M scaler output is 11th-order noise-shaped to 24 bits at 768k for -301 dB accuracy, ranks Gaussian dither above TPDF, and advises keeping the source bit perfect. Head-Fi, Dec 2019
2020-01-02Watts says optical is the best input because it carries no RF noise; RF entering non-linear analog electronics intermodulates with the audio, spreading noise across the bandwidth. Passion for Sound 10:34
2020-01-02Watts says RF causes noise floor modulation; adding RF filters to Hugo 2's USB made it sound like optical, unlike Hugo, with no measurable change, so unmeasurable modulation matters. Passion for Sound 12:11
2020-01-10Watts says SPDIF is always 24 bits and USB 32 bits, with shorter words zero-padded, so Hugo 2 handles any bit depth automatically. Head-Fi, Jan 2020
2020-01-20Watts explains isolating output-stage supply currents, shown in TT2's distortion plot, says delay follows tap length and oversampling, describes the M scaler's asymmetric video filter, and heard no USB-optical difference. Head-Fi, Jan 2020
2020-01-29Watts advises PCM unless an SACD's master was DSD, says he is making mains-powered USB match optical and battery, and warns modifying his optimized designs more likely harms than helps. Head-Fi, Jan 2020
2020-02-09Watts says USB data error rates with a certified type 2 cable are too low to worry about, and errors would be obvious as clicks and dropouts with DoP. Head-Fi, Feb 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
2020-02-11Watts says the remote uses standard RC5 code, mentions flying to CanJam NYC, and says proper DSP cannot create clicks while faulty USB data is a non-linear manipulation. Head-Fi, Feb 2020
2020-02-13Watts says USB, like SPDIF, carries only audio data and supports no commands. Head-Fi, Feb 2020
2020-02-26Watts says 352k over optical is near impossible because optical transmitters and receivers cannot handle it, so the poster's source is probably downsampling to 176.4 kHz. Head-Fi, Feb 2020
2020-04-09Watts says USB decoding and galvanic isolation work down to 3.3v VBUS, and the gain from better-than-16-bit over 13-bit timing varies by listener, but he needs the M scaler. Head-Fi, Apr 2020
2020-04-10Watts says Chord desktop DACs and the M scaler need 5v VBUS to power USB galvanic isolation, and portable DACs need VBUS on as a USB-connected flag. Head-Fi, Apr 2020
2020-04-26Watts says connector impedance mismatch does not matter thanks to reflection cancellation and the FPGA's 15 nS anti-glitch, but the cable itself must be 75 ohms. Head-Fi, Apr 2020
2020-05-04Watts says the JitterBug helped Hugo 1, suspects USB treatments add brightening RF, heard no USB-optical difference on M scaler or ungrounded Hugo 2, and enjoys Tangerine Dream box sets. Head-Fi, May 2020
2020-05-05Watts says data integrity plays no part, as long M scaler tests at -200dB never showed a bit error, but injected noise and processor activity can change the sound. Head-Fi, May 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
2020-06-25Watts says Qutest's BNC inputs take 768 kHz without transformers at 75 ohms, it was not designed for slow-ramping PSUs, and non-stock supplies void Chord's warranty. Head-Fi, Jun 2020
2020-08-23Watts explains optical injects far less RF noise than USB because the receiver has no processing, ferrites on optical made no difference, and it blocks source ground currents. Head-Fi, Aug 2020
2020-10-19Watts says a poster's USB versus optical difference on Dave fits RF raising noise floor modulation, though he heard only a tiny change, and says he has heard NFM below -180 dB. Head-Fi, Oct 2020
2021-03-19Watts says optical cannot pass source ground-plane noise, mains ground loops are mostly theoretical, and suggests a phone with a bit-perfect app as a reference source. Head-Fi, Mar 2021
2021-04-07Watts says USB can equal optical, as with his old MSI laptop, but on his new desktop PC optical sounded clearly better; with noisier sources optical wins. Head-Fi, Apr 2021
2021-04-07Watts says his earlier laptops sounded the same on optical and USB, and explains his PC's large PSU and CPU choice for Xilinx simulation tools. Head-Fi, Apr 2021
2021-05-31Watts says Hugo 2's USB sensitivity depends on mains loops, advises optical and avoiding DDCs in mains systems, and explains RF-induced noise floor modulation as brightness. Head-Fi, May 2021
2021-06-16Watts says the best setting depends somewhat on the pre-amp, AES is technically inferior to BNC, and as it is not a solid RF standard Chord plays safe with 88kHz. needs context Head-Fi, Jun 2021
2021-08-11Watts says TT2's coax receiver stays powered in standby, so sharing a coax source with another DAC is no problem. Head-Fi, Aug 2021
2022-01-31Watts says the brief required Poly compatibility; a planned second USB-C port for charging conflicted with the optical input, and he refused to drop optical. Darko.Audio 2:22
2022-01-31Watts agrees, noting the original Hugos and Mojos did the same, and says the 3.5 mm connector's advantage is that it is very small. Darko.Audio 3:34
2022-01-31Watts says the 768 kHz coax capability is so that it can be run with the M Scaler. needs context Darko.Audio 4:25
2022-02-15Watts attributes HF errors to ADC noise shapers and decimation, keeps HF filter off on DAVE via M Scaler, prices the Choral M Scaler at DAVE level, and rejects XMOS. Head-Fi, Feb 2022
2022-02-22Watts says optical versus USB depends on the source, identical on his laptop but optical better on his design PC; battery sources off mains make no difference. Head-Fi, Feb 2022
2022-03-19Watts says optical is best but USB can sound identical; with portable sources it does not matter, but earthed, USB sounds brighter, hence isolated USB on desktop DACs. MFG Audio Reviews 56:15
2022-03-19Watts says Mojo and Hugo 2 lack galvanic isolation and that galvanic isolation in general is about 99% effective; optical helps with noisy servers, and his MSI desktop sounds much better on optical. MFG Audio Reviews 56:58
2022-03-19Watts says it depends on the system; USB can fundamentally sound the same as optical, and the issue is circulating RF noise currents. MFG Audio Reviews 57:44
2022-03-19Watts says yes, the USB is pretty much the same on it. needs context MFG Audio Reviews 57:58
2022-03-27Watts recounts redesigning Qutest's regulation after Qute proved PSU sensitive, admits his 2016 USB preference on Dave was RF brightness, and calls optical the reference input. Head-Fi, Mar 2022
2022-03-28Watts details SPDIF word clock extraction and his frequency-locked DPLL on a 104.25MHz clock, and says USB can match optical but RF leaks through the 2pF isolation. Head-Fi, Mar 2022
2022-03-28Watts says USB cannot outperform optical apart from optical's 192k limit, and aims for future DACs immune to source and PSU RF, which cause noise floor modulation. Head-Fi, Mar 2022
2022-04-29Watts says Mojo was never double; the USB decoder draws 253 mW and the optical receiver 13 mW, giving about 15% more battery life on optical or coax. Head-Fi, Apr 2022
2022-05-01Watts says Mojo 2's USB decoder has its own regulation and RF filters, he is independent of Chord, and two headphone sockets were kept for reliability and sharing. Head-Fi, May 2022
2022-05-07Watts prefers optical over coax, uses regular optical cables plus a 2m Lifatec optical cable for 192k and Wave Stream BNC cables on the M scaler, and sees no benefit in I2S or balanced. Head-Fi, May 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
2022-07-12Watts says optical output from his Windows 10 PC's MSI motherboard, and from his old MSI laptop, handles 88.2, 176.4 and DoP DSD64 without problems. Head-Fi, Jul 2022
2022-08-19Watts says he prefers optical into the M Scaler; USB can match it or sound harder, brighter and flatter; BNC is technically worst, lacking galvanic isolation. AVstore 41:06
2022-08-19Watts says the M Scaler's BNC outputs have a galvanic isolator, giving near-optical standard, but about three picofarads (first said two) is tens of ohms at gigahertz, so he also added ferrites and filters. AVstore 42:06
2022-08-19Watts says to use optical as the reference since it is perfectly galvanically isolated, and its slightly higher jitter than BNC does not matter with Chord DACs. AVstore 42:56
2022-09-07Watts confirms TT2 needs 5V on the USB cable because its galvanic isolator is powered from the USB +5V. Head-Fi, Sep 2022
2022-10-03Watts says USB sounding different from optical on TT2 is RF noise through the isolator's 2pF coupling, causing brightness, and a £9.29 5m plastic optical cable equals his glass one. Head-Fi, Oct 2022
2022-10-04Watts says all wired connections must be removed from the source when using optical, and a USB-to-optical converter should need no external supply; the Douk Audio U2 looks worth trying. Head-Fi, Oct 2022
2022-12-13Watts says audiophile USB cables add RF or sound identical, optical (KableDirekt) is best, a phone or battery laptop is the reference source, and Wave Stream cables help. Head-Fi, Dec 2022
2023-02-04Watts says with his MSI laptop into the M Scaler and Dave, optical and USB sounded the same so he used USB, before his son built him a high-performance computer. Dusty Audio 1:07:10
2023-02-04Watts says his 800 W desktop's USB sounded significantly worse than optical into the M Scaler; optical is the reference because no current flows into the DAC. Dusty Audio 1:07:51
2023-02-04Watts says the source does not really matter, but use optical as the reference to judge it. Dusty Audio 1:08:42
2023-02-05Watts says processing the clock is the problem: his SPDIF receiver converts to I2S inside the FPGA, so the clock question remains either way. Soundnews 45:20
2023-02-05Watts says the issue is converting an asynchronous clock to a synchronous one, not the number of lines; jitter arrives the same via a direct clock input or SPDIF decoder. Soundnews 46:01
2023-02-05Watts says 2 microseconds is a thousand times real-world jitter, so better clocks are unneeded; an I2S 64FS bit clock cannot serve his 2048FS master clock anyway. Soundnews 48:12
2023-02-05Watts says separate I2S clock lines bring no benefit and three cables add ground noise; he always prefers optical, with galvanically isolated BNC from the M Scaler nearly matching it. Soundnews 48:58
2023-02-05Watts says isolated BNC is not quite as good as optical; non-isolated BNC is much worse; USB follows, isolated on TT2 and DAVE; optical is the primary reference input. Soundnews 49:45
2023-02-05Watts says optical carries 24 bits at 192 kHz and asks how many recordings exceed that. Soundnews 50:23
2023-03-01Watts says 2pF across the M Scaler's USB and BNC isolation gives about 80 ohms at 2 GHz, letting current reach DAVE's ground plane; optical may beat USB, source depending. Head-Fi, Mar 2023
2023-06-18Watts says an isolated power bank or Wave cables break the M Scaler's GHz ground loop, longer standard BNC sounds better via common mode inductance, and Krisdonia sounded worse. Head-Fi, Jun 2023
2023-11-30Watts says a Roon resync delay fixes USB sample-rate-change clicks by flushing buffers, and optical from the streamer avoids them, limited to 192k, often with better sound. Head-Fi, Nov 2023
2024-02-06Watts says optical makes no difference or sounds warmer with better depth than USB, since source jitter does not matter but RF ground currents can, making Toslink the reference. Head-Fi, Feb 2024
2024-02-29Watts says optical is the reference input for Mojo 2, while USB from a quiet or battery-powered source such as a phone sounds identical, given bit-perfect data. Head-Fi, Feb 2024
2024-03-20Watts says Toslink optical, usually considered the worst digital connection, is in his opinion the best, and introduces the contentious myth that linear power supplies must beat switch mode. MFG Audio Reviews 45
2024-03-20Watts says a low-power battery source removes both correlated and random RF noise, giving better depth and a warmer sound, and that optical, reputedly worst, is best because coupling capacitance is zero. MFG Audio Reviews 22:54
2024-03-20Watts says with optical everything is done by light, so there is no coupling capacitance. MFG Audio Reviews 23:41
2024-03-20Watts says optical blocks correlated and random RF noise; it often has worse jitter, though his Audio Precision ATS2 measured less on optical than BNC, and his DPLL removes this. MFG Audio Reviews 23:47
2024-03-20Watts says optical should be the reference connection; USB can sound identical with a low-power battery source, and on an old MSI laptop USB and optical sounded the same. MFG Audio Reviews 24:40
2024-03-20Watts says his powerful MSI design computer shows substantial differences between optical and BNC, and in his tests high-end USB cables tend to sound brighter by increasing RF noise. MFG Audio Reviews 25:32
2024-03-20Watts says in every listening test they sound the same because current causes the problem; without current there are no ground-plane voltage drops, and perfect ground planes are impossible. MFG Audio Reviews 1:00:30
2024-04-15Watts shares CanJam slides: optical sounds warmer from less noise floor modulation, USB's etched sound is mistaken for transparency, and with isolated sources USB and BNC can match optical. Head-Fi, Apr 2024
2024-04-16Watts says RF noise scales with circuit power, Toslink lowest and USB two orders worse; he still RF-filters optical, and more pulse array elements give lower noise, distortion and impedance. Head-Fi, Apr 2024
2024-05-16Watts answers that the scaler's source inputs are USB, optical and BNC. needs context ConvinceMeAudio 11:31
2024-07-18Watts says it depends on the source: using optical, plug and unplug the USB, and if no difference is heard, keep it plugged in. Head-Fi, Jul 2024
2024-08-12Watts says inputs differ only through source RF noise: optical is the reference, USB has ground ferrites, and coax is most sensitive, hence galvanic isolation on the Hugo M Scaler. Head-Fi, Aug 2024
2024-11-22Watts corrects himself: USB sounded brighter on 2Qute from noise floor modulation, not better clocking, as a later test found USB and optical identical; listening tests easily mislead. Head-Fi, Nov 2024
2025-03-27Watts says DoP works on all inputs within rate limits (optical DSD64, coax up to DSD128), conversion keeps DSD's 6dB overload, and test modulators show DSD is technically unacceptable. Head-Fi, Mar 2025