Pre-ringing, phase and rival filter designs

Reconstruction filters and timing

Answers on this topic

• Do Chord DACs decode MQA, and what does Rob think of it?
• Isn't pre-ringing bad? Why doesn't Chord offer minimum-phase, apodizing or NOS filters, and are NOS DACs really bit perfect?
• Should I upsample in software (HQPlayer, PGGB or my player) before a Chord DAC, and can it match an M Scaler?

Everything he said on this topic (117)

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

• 2015-06-18Watts explains the pulse array's analog-like distortion, why half-band filters keep original samples, and how a 256-tap WTA beat a 2048-tap half-band Kaiser filter in the late 90s. Head-Fi, Jun 2015
• 2015-06-18Watts says half-band filters time transients poorly (-6dB at FS/2); 16-bit sinc accuracy needs about 1M taps; Hugo is about 12 bits, Dave about 14. Head-Fi, Jun 2015
• 2015-10-03Watts rebuts a Nagra DAC's marketing claims point by point: quantization noise, brickwall filter phase, oversampling as cheating, clocking, and DSD out-of-band noise. Head-Fi, Oct 2015
• 2016-03-31Watts poses a paradox: an ideal infinite sinc filter rings infinitely yet reconstructs a bandlimited signal unchanged, and says the industry's push to minimize ringing gets filters wrong. Head-Fi, Mar 2016
• 2016-04-10Watts says an ideal sinc filter's infinite ringing reconstructs bandlimited signals perfectly, and that pre-ringing worries come from testing with non-bandlimited impulses. Head-Fi, Apr 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
• 2016-05-17Watts says an ideal sinc reconstruction filter adds no ringing, but theory says nothing on how an ADC should bandlimit; Davina will test aliasing rejection beyond 140 dB. Head-Fi, May 2016
• 2016-05-17Watts says ringing never explained differences he heard tuning WTA, an ideal filter must ring, 8FS and 16FS filters with identical ringing sound different, and ADC ringing likely matters little. Head-Fi, May 2016
• 2016-07-24Watts says keeping digital data unchanged or minimizing ringing are wrong goals; a DAC's purpose is to reproduce the analog waveform at the A-to-D converter. Hifistatement 0
• 2017-01-07Watts presents the Blu Mk2 slides: why ringing worries are mistaken, the 16-bit case for about 1M taps, delaying launch to reach 1M, and why the scaler is separate. Head-Fi, Jan 2017
• 2017-05-13Watts says MQA interpolation filters, with huge timing errors due to aliasing, sounded dreadful against the WTA filter, and urges listeners not to assume MQA is better. Head-Fi, May 2017
• 2017-05-18Watts says MQA interpolation filters sound dreadful against a standard WTA filter compared on a Mojo, and that MQA's aliasing is unacceptable, so he refuses to implement it. Head-Fi, May 2017
• 2017-08-26Watts says Blu 2's low-latency video option cuts delay from 630 mS to 104 mS via an asymmetric filter but degrades sound, so he sets -630 mS in JRiver. Head-Fi, Aug 2017
• 2017-10-13Watts says a minimum-phase or 'IR' filter, any filter with no pre-ringing, gives 100 microseconds of timing error and loses the transient's start, while an infinite sinc filter reconstructs it perfectly. miceblue425 12:06
• 2017-10-13Watts poses a paradox: a sinc filter perfectly reconstructs a signal, yet an impulse fed into it comes out looking nothing like the impulse. miceblue425 16:17
• 2017-10-13Watts says everyone calls pre-ringing the evil of audio and holds that long filters with lots of ringing are bad and ringing should be minimized, and that everybody is wrong. miceblue425 17:00
• 2017-10-13Watts says a Dirac impulse is an illegal, non-bandwidth-limited signal: useful for showing a filter's coefficients, never for judging its sound, since bandlimited signals have zero output at FS/2. miceblue425 17:25
• 2017-10-13Watts says a Dirac has the same level at 22.05 kHz as at DC, and the audio business is wrong to judge filter sound quality from Dirac responses. miceblue425 18:10
• 2017-10-13Watts explains that each sample's impulse response carries pre-ringing that sums with the others to rebuild the waveform where the data is zero, with no stray pre-ringing for bandlimited signals. miceblue425 18:49
• 2017-10-13Watts says pre-ringing is essential to reconstruct transients properly. miceblue425 19:34
• 2017-10-17Watts says taps are simply taps, rivals' short or minimum-phase filters misreconstruct transient timing, Blu 2 sounds profoundly better, and he predicts marketing pseudo tap counts. Head-Fi, Oct 2017
• 2017-10-18Watts says with bandwidth-limited signals longer filters ring less, pre-ringing is needed for transients, half-band brickwall filters alias badly, and slow roll-off beats them but loses to proper brickwalls. Head-Fi, Oct 2017
• 2017-10-20Watts says sinc ripples drop below 16-bit level near a million taps; doubling adds 1 bit. DAVE is about 13 bits, Blu beyond 16, NOS 1, MQA 3 or 4. Hifistatement 24
• 2017-10-20Watts rates a typical high-performance DAC at 6 or 7 bits accurate, Hugo 12, DAVE 13.5, Blu beyond 16, and says ringing is irrelevant because it comes from non-bandlimited impulses. Hifistatement 1:12
• 2017-10-20Watts says filter tests use an illegal impulse with output at FS/2; a bandlimited impulse gives no extra ringing in his filters, and a sinc filter returns it exactly. Hifistatement 1:58
• 2017-10-20Watts says the paradox of a filter that rings infinitely yet recovers everything perfectly arises only because the test signal is not bandwidth limited when it should be. Hifistatement 2:51
• 2017-12-02Watts says sampling theory only requires bandwidth limiting, which may use a non-pre-ringing IIR filter; his pre-ringing remark concerned DAC interpolation filters, and coefficient calculation matters beyond tap length. Head-Fi, Dec 2017
• 2017-12-18Watts calls NOS DACs an unmitigated disaster for transparency, with massive transient timing errors and out-of-band images, and says they sound soft, flat and out of focus. Head-Fi, Dec 2017
• 2017-12-26Watts says the only exact reconstruction is an infinite sinc interpolation filter: linear phase and a brick wall rather than slow roll-off, with infinite pre-ringing. Audiophile Style, 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
• 2018-02-23Watts says time-domain debates about pre-ringing and NOS designs get it wrong: NOS appeals because it reproduces the data, but a DAC should reproduce the original analog signal. MajorHiFi 2:37
• 2018-03-06Watts says Hugo 2/Qutest use 67.5mS of data versus 1mS for conventional filters, minimum phase sounds soft, the M scaler uses 1.37 seconds, and more M scalers will follow. Head-Fi, Mar 2018
• 2018-05-14Watts cites Archimago's articles, calls MQA a lossy distortion-generating codec with 1% THD and noise at 20 kHz, and worries its rendering creates transient timing errors by avoiding pre-ringing. Head-Fi, May 2018
• 2018-07-01Watts says AAC, short filters, MQA, minimum phase, NOS and DSD sound soft and warm from transient timing uncertainty; turning off the incisive filter similarly sounds warmer. Head-Fi, Jul 2018
• 2018-07-21Watts illustrates with a sampled 20 kHz sine-wave burst, saying a simple conventional filter such as a NOS, IR or MQA filter produces a different waveform from the original. c w 9:57
• 2018-07-21Watts says a filter allowing no pre-ringing loses the original pulse, an error of about 100 microseconds, while a sinc function filter perfectly reconstructs the bandlimited transient. c w 10:54
• 2018-08-10Watts says MQA's filter sounds much worse than WTA, and its compression to 44.1/48 adds a notch, 1% aliasing distortion at 20kHz and lossy coding to about 17 bits. Head-Fi, Aug 2018
• 2018-08-10Watts answers 'both', adding that low tap length linear phase filters also sound soft and bloated in the bass, with poor bass pitch discrimination. needs context Head-Fi, Aug 2018
• 2018-08-19Watts says a claimed 10,000,000-tap filter has a very poor transition band that a few thousand taps could match; Mojo's WTA is 10 times better, and algorithm beats tap length. Head-Fi, Aug 2018
• 2018-09-01Watts explains that 16-bit accuracy refers to the ideal sinc, errors arise only with transients, NOS is crude sample-and-hold, and delta-sigma ADCs suffer half-band decimation aliasing. Head-Fi, Sep 2018
• 2018-09-19Watts calls the claim that filter ringing is reverb pseudoscience: a sinc interpolation filter reconstructs a bandlimited impulse perfectly, with no ringing at all. Head-Fi, Sep 2018
• 2018-09-26Watts says he designed IIR and FIR Davina decimation filters with over 250 dB rejection to test bandlimiting; he expects pre-ringing at 22.05 kHz to prove a red herring. Head-Fi, Sep 2018
• 2018-12-13Watts illustrates sampling a 20 kHz tone burst and says simple filters such as NOS, IIR or MQA filters reproduce the digital data without the original transient shape. Pursuit Perfect System 5:23
• 2019-03-29Watts says TT2 filters are interpolation tweaks not EQ, argues NOS DACs are not truly bit perfect, explains transient timing errors, and warns IIR EQ and dithered volume are not transparent. Head-Fi, Mar 2019
• 2019-04-09Watts says ringing is inaudible because 22.05 kHz is inaudible and bandlimited signals carry no energy there, calling the industry's Dirac-impulse view a misunderstanding of sampling theory. Head-Fi, Apr 2019
• 2019-04-10Watts attacks the industry's 'ringing is bad' meme, discusses ultrasonic intermodulation, distinguishes EQ pre-ringing from reconstruction, and calls transient timing the real problem. Head-Fi, Apr 2019
• 2019-04-11Watts compares his FIR and IIR Davina decimation filters on a square wave, explains phase linearity, says both reach 250 dB rejection, and expects FIR to sound better. Head-Fi, Apr 2019
• 2019-07-15Watts says NOS DACs do oversample, with a zero-order hold, the crudest filter possible, whose large timing and aliasing errors make music sound soft, flat and out of focus. Head-Fi, Jul 2019
• 2019-09-14Watts says the industry misunderstands reconstruction, so minimum phase, NOS and no-ringing filters worsen timing, and fitting sinc to finite processing by listening and custom windowing is the real work. Head-Fi, Sep 2019
• 2019-12-19Watts says early digital sounded bad half from interpolation filters and half from converter issues, and that the industry avoids sinc functions because it treats ringing as bad. Passion for Sound 12:09
• 2019-12-19Watts says the industry is wrong because sampling theory requires a bandwidth-limited signal: content may reach 22.04 kHz but must be zero at 22.05 kHz. Passion for Sound 15:14
• 2019-12-19Watts says an impulse is not bandwidth limited; a bandwidth-limited impulse through a sinc function does not ring, but through MQA or minimum phase filters it rings excessively. Passion for Sound 15:30
• 2019-12-19Watts says the job is reconstructing between samples; a NOS filter is a crude first-order hold with huge transient errors, e.g. losing the first pulse of a 20 kHz burst. Passion for Sound 17:48
• 2020-01-02Watts says offering minimum phase, NOS and other filter options would have been easy and commercially sensible, but he will not offer options he knows sound worse; WTA sounds best. Passion for Sound 16:34
• 2020-01-02Watts says MQA uses a short minimum-phase type filter that looks only into the past; calling pre-ringing bad misreads sampling theory, since sinc pre-ringing is essential for perfect reconstruction. Passion for Sound 18:00
• 2020-01-02Watts says that once a filter stops looking into the future, you get huge transient errors. Passion for Sound 18:46
• 2020-01-02Watts says pre-ringing looks unnatural, but sinc ringing occurs at 22.05 kHz, which is inaudible, and a properly bandlimited signal would not ring at all. Passion for Sound 19:20
• 2020-01-02Watts says an impulse is an illegal signal that reveals coefficients, not behavior on music; with bandlimited signals WTA rings less than minimum-phase MQA-type filters, which add ringing. Passion for Sound 19:48
• 2020-01-02Watts says people like MQA or minimum phase because their huge transient errors put sound out of focus, warmer and smoother, taming a DAC made bright by noise floor modulation. Passion for Sound 20:31
• 2020-01-02Watts says the better approach is a DAC warm and free of noise floor modulation, reconstructing transients with a sinc function, giving sharp sounds without aggression and rich saxophone. Passion for Sound 21:23
• 2020-01-02Watts says people may prefer NOS, MQA or minimum-phase filters on inferior DACs because they artificially soften the sound. Passion for Sound 21:48
• 2020-07-24Watts says conventional phase shift seems unimportant but phase varying with time or amplitude is audible, defends sinc ringing for bandlimited signals, and discusses SMPS design and USB isolation. Head-Fi, Jul 2020
• 2020-07-26Watts says price is irrelevant: Mojo drives 8 ohm speakers, reconstructs transients better than Bartok's minimum phase filters and lacks Bartok's noise floor modulation. Head-Fi, Jul 2020
• 2021-05-23Watts says PGGB uses an apodizing, slow roll-off filter rather than sinc, so long taps cannot help its transient timing, and true offline sinc sounds like the M scaler. Head-Fi, May 2021
• 2021-05-23Watts quotes PGGB's FAQ on apodizing and says its windowing function turns sinc into something that should not be called sinc; true offline sinc needs no window. Head-Fi, May 2021
• 2021-06-02Watts says PGGB uses a slow roll-off apodizing filter for 44.1k, so many taps cannot fix transient timing; samples he heard sounded flatter, softer and less separated. Head-Fi, Jun 2021
• 2021-06-02Watts quotes PGGB's FAQ on apodizing and says a slow roll-off interpolation filter cannot reconstruct bandlimited signals and seriously degrades transient timing, making long taps pointless. Head-Fi, Jun 2021
• 2022-03-19Watts illustrates with a sampled sine-wave burst and begins to show what conventional, IIR, NOS, MQA and minimum phase filters do to it. MFG Audio Reviews 18:09
• 2022-03-19Watts says those filters lose the initial transient, a 100 microsecond timing error, so they sound soft, which some like because it hides the DAC's noise floor modulation. needs context MFG Audio Reviews 18:55
• 2022-03-19Watts says the cure is to remove both noise floor modulation and timing errors, and that an ideal sinc filter recovers the transient's starting point because it pre-rings and post-rings. MFG Audio Reviews 19:39
• 2022-05-09Watts says decimation filters need only adequate aliasing rejection and FIR pre-ringing was inaudible, but DAC interpolation needs a sinc, so he offers one WTA1 filter, no options. Head-Fi, May 2022
• 2022-05-10Watts says decimation needs only removal of everything above the new Nyquist, so IIR works, but interpolation creates new samples and only a sinc reconstructs them perfectly. Head-Fi, May 2022
• 2022-05-13Watts agrees conventional ADCs soften sound through limited HF accuracy and aliasing, says minimum-phase, MQA, apodizing and NOS filters soften it far more, and defends sampling theory. Head-Fi, May 2022
• 2022-06-22Watts says a NOS filter is the crudest oversampling filter, real filters degrade transient timing, and PWM in Class D has amplitude-dependent timing plus filter phase intermodulation. Head-Fi, Jun 2022
• 2022-07-14Watts says the M Scaler is essential, PGGB sounded like an apodizing filter, and the M Scaler reconstructs transient timing beyond 16 bits, passing -301 dB via dual BNC. Head-Fi, Jul 2022
• 2022-07-15Watts says removing pre-ringing harms transient reconstruction, impulses are illegal non-bandlimited signals, and his test filtering 20-22.05 kHz ADC aliasing after WTA1 gave little or no benefit. Head-Fi, Jul 2022
• 2022-08-21Watts says WTA uses five variables tuned by thousands of listening tests, the algorithm matters more than tap length, and a two-sample linear interpolation filter would be a disaster. Head-Fi, Aug 2022
• 2023-02-04Watts says MQA degrades transients, with very limited taps and aliasing, measured at 1% distortion above 20 kHz, and that its makers have no listening tests showing aliasing is harmless. Dusty Audio 55:01
• 2023-02-04Watts says MQA ignores transient reconstruction; he heard enormous degradation from its interpolation filters, so Chord refused MQA, losing customers at the time. Dusty Audio 55:44
• 2023-02-05Watts says this thinking leads to NOS DACs, and that 'no oversampling' is the wrong term because they do oversample. Soundnews 14:30
• 2023-02-05Watts says sample-and-hold is a first-order digital filter and oversampling; converting sampled data to a continuous waveform is infinite oversampling, so even a NOS DAC oversamples. Soundnews 14:48
• 2023-02-05Watts says NOS is the crudest filter; in digital, more complex means more accurate reconstruction and better sound, the opposite of analog, but both are about accuracy. Soundnews 15:35
• 2023-03-26Watts says his NVIDIA streamer allows a one second video delay so he can use an M Scaler; original PGGB files sounded nothing like it, and apodizing cannot reconstruct transients. Eric's Hi-Fi 11:13
• 2023-08-22Watts disputes PGGB's pure-sinc claims, says coefficients must be windowed, and suggests listening for bass pitch, separation, focus and timbre variation. Head-Fi, Aug 2023
• 2023-10-01Watts says he could put other filters into the interpolation filter (transcribed 'a nozzle', perhaps NOS) to change the sound, but that would mess it up, so he does not. The Source AV 37:04
• 2023-10-30Watts says the ADC is a simple 2-channel unit for Blumlein ribbon recording, separate clocking is solved, and non-delay asymmetric FIR filters give poor transient reconstruction. Head-Fi, Oct 2023
• 2023-11-02Watts says an asymmetric FIR with short pre-ringing and long post-ringing beats short symmetric filters, as in the Hugo M Scaler's video mode. Head-Fi, Nov 2023
• 2023-11-13Watts says converting to NOS would take zero effort but destroy musicality, as NOS is a first-order hold filter with the worst transient timing performance. Head-Fi, Nov 2023
• 2023-12-02Watts says a bandwidth-limited square wave must show ringing, and a DAC that reproduces one without ringing fails in the time domain. Head-Fi, Dec 2023
• 2023-12-02Watts says his DACs reproduce square waves with correct ringing and Gibbs overshoot, without clipping thanks to filter headroom, and a DAC without ringing is not bandlimiting. Head-Fi, Dec 2023
• 2024-07-12Watts says digital needs complexity, ideally infinite taps; a NOS filter is a first-order hold, the crudest interpolation filter, liked mistakenly because it sounds soft and warm. HIFICLUB 28:56
• 2024-07-12Watts says NOS filters sound soft and warm because their transient errors reach 100 microseconds; better transient reconstruction sounds sharper and more focused, like a camera lens. HIFICLUB 29:50
• 2024-07-12Watts says transient errors blur everything, making NOS sound unnaturally warm and soft; digital improves with complexity unless it adds analog noise problems. HIFICLUB 30:32
• 2025-03-26Watts explains causal versus symmetric acausal filters, says interpolation pre-ringing at 22kHz is not an issue but EQ should be causal, and lists his CanJam schedule. Head-Fi, Mar 2025
• 2025-05-12Watts says a simple interpolation filter gives a transient error of around 100 microseconds, as do NOS, IR, minimum phase and MQA filters; an infinite sinc filter reconstructs perfectly. Audiophile Junkie 5:21
• 2025-05-12Watts says everyone in the business calls pre-ringing bad, and that everybody is wrong. Audiophile Junkie 6:59
• 2025-05-12Watts says pre-ringing is essential to recover transient timing, that more pre-ringing means more accurate reconstruction, and that a bandlimited impulse is perfectly reproduced by a sinc filter. Audiophile Junkie 7:18
• 2025-05-12Watts says that despite infinite pre- and post-ringing, the original impulse ends up perfectly reconstructed. needs context Audiophile Junkie 8:02
• 2026-03-17Watts says leaving the data unfiltered gives a distorted signal with stepped edges unlike a 20 kHz sine; in 1980 he calculated 16-bit reconstruction needed well over half a million FIR taps. ecoustics 10:35
• 2026-03-17Watts says every DAC has a digital interpolation filter; even a NOS DAC is really a filter that holds the data. ecoustics 22:30
• 2026-03-17Watts says NOS filters worsen timing errors so transients blur and the sound turns soft and warm, which can mask a hard, bright DAC with noise floor modulation. ecoustics 22:56
• 2026-10-02Watts says a NOS DAC still uses a digital interpolation filter, holding each sample value, the crudest oversampling filter possible. HiFi Buys 41:39
• 2026-10-02Watts calls NOS a first-order hold with the biggest transient timing errors, so it sounds soft and warm, offsetting the hardness of high-frequency distortion. HiFi Buys 42:01
• 2026-10-02Watts says more taps approach the ideal infinitely sharp sinc; claims that its ringing is wrong misunderstand sampling theory, which requires zero energy at FS/2. HiFi Buys 1:50:29
• 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 ironically a band-limited impulse rings more through a short-tap-length filter than through a long one. HiFi Buys 1:52:00
• 2026-10-02Watts says this filter rings for three seconds with three seconds of pre-ringing because it looks at six seconds of music, yet a properly band-limited impulse shows no ringing. HiFi Buys 1:52:19
• 2026-10-02Watts says a minimum-phase filter or one with a limited number of taps will ring. HiFi Buys 1:52:37
• 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
• 2026-10-02Watts says theorists who call ringing unnatural are not reading the maths correctly: the signal must be band-limited and a Dirac impulse is not. HiFi Buys 1:55:48
• 2026-10-02Watts says an ideal sinc filter would pre- and post-ring forever and look awful, yet would reproduce the original signal perfectly as long as it is band-limited. HiFi Buys 1:56:34
• 2026-10-14Watts defines pre-ringing as ringing before an impulse and post-ringing after, saying the best interpolation filter, a sinc function, has infinite amounts of both. Part-Time Audiophile 24:20
• 2026-10-14Watts says people object to pre-ringing as a response to the future, yet sampling theory is proven with a sinc function that perfectly reconstructs the signal. Part-Time Audiophile 25:08
• 2026-10-14Watts says sampling theory reconstructs bandwidth-limited signals, needing exactly zero output at 24 kHz for 48 kHz sampling, whereas an ideal impulse has equal energy at all frequencies. Part-Time Audiophile 25:57
• 2026-10-14Watts says a bandwidth-limited impulse through a sinc filter shows no pre- or post-ringing, while 'audiophile' reduced-ringing filters actually ring; sinc matters for transient timing reconstruction. Part-Time Audiophile 27:12
• 2026-10-14Watts says the NOS filter used by R2R DACs is an oversampling first order hold filter, the worst for transient timing, making sound artificially soft, smooth and warm. Part-Time Audiophile 39:00