Error classes and which are audible

Evaluation method and design philosophy

Answers on this topic

• What is a transient timing error, and why is it audible when a fixed delay or phase shift is not?
• Which kinds of error does Rob consider audible, and which does he consider benign?

Everything he said on this topic (40)

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

• 2015-12-01Watts ties depth to small-signal linearity, distinguishes it from noise floor modulation, and describes raising Dave's noise shapers from 200 to 350 dB with depth improving throughout. Head-Fi, Dec 2015
• 2015-12-11Watts defines musicality as emotional involvement, achieved by reducing errors the brain cannot decode: timing (long taps), small-signal accuracy for depth (2048FS noise shapers), and noise floor modulation. Head-Fi, Dec 2015
• 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
• 2016-04-02Watts contrasts fixed analog noise with signal-dependent small-signal distortion in R2R, delta-sigma and DSD DACs, and says DAVE's -127 dB dynamic range is set by hiss alone. Head-Fi, Apr 2016
• 2016-10-16Watts argues musicality comes first and explains why Mojo and DAVE excel on transient timing (NOS errors, tap length, 1M taps), small-signal accuracy and noise floor modulation. Head-Fi, Oct 2016
• 2017-07-23Watts says phase varying with frequency is unimportant but timing varying with amplitude or sampling matters, as in inductors, so digital direct drive replacing passive crossovers is planned. Head-Fi, Jul 2017
• 2017-12-05Watts says higher-order harmonics and anharmonic distortion are very audible because the brain subtracts the ear's own harmonic distortion but cannot subtract anharmonics, which do not occur naturally. RMAF 12:07
• 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
• 2018-04-04Watts says since Hugo bad recordings became enjoyable, concluding the brain copes with noise, harmonic distortion and frequency response but not digital's unnatural distortions. Head-Fi, Apr 2018
• 2018-12-12Watts says increasing variation means progress toward transparency, and names three key DAC failings: noise floor modulation (refinement, timbre), small-signal accuracy (detail, depth) and transient reconstruction. Pursuit Perfect System 8:19
• 2018-12-12Watts says all DACs create noise; a fixed noise is unimportant, like background air conditioning, but the problem is noise that changes with the signal. Pursuit Perfect System 9:36
• 2020-02-22Watts says it is fixed resistor thermal noise, and fatigue only sets in when noise modulates with the signal. needs context Head-Fi, Feb 2020
• 2020-06-25Watts says odd order harmonics sound worse because the ear generates second harmonic the brain compensates for, then recalls DAVE's three or four prototypes aimed at maximum linearity. Part-Time Audiophile 32:35
• 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
• 2021-01-03Watts favors old-school active speakers over multiple resampling, says phase that shifts with amplitude matters while amplitude-linear phase shift shows no evidence of mattering, and is researching direct driver drive. Head-Fi, Jan 2021
• 2021-03-06Watts says the brain evolved to handle room acoustics but not noise floor modulation, aliasing and small-signal errors, and no commercial plans exist yet for speakers. Head-Fi, Mar 2021
• 2021-03-29Watts compares dCS Bartok's quoted noise and headphone output (1.4W into 33 ohms) with TT2's 10W, and says fixed noise at -127dB is inaudible while signal-dependent noise matters. Head-Fi, Mar 2021
• 2021-03-29Watts declines to discuss future products, describes a -350dB artifact his son identified blind, and says pulse array residual noise is resistor thermal noise traded against distortion. Head-Fi, Mar 2021
• 2021-05-04Watts says MP3 encodes transients poorly and sounds soft, phase or frequency response errors are not damaging, and his ADC work will test 768k to 48k and back. Head-Fi, May 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
• 2021-11-30Watts lists his flight and hotel kit, says measurements catch gross flaws, and that the brain compensates for transducer distortion but not digital errors like NFM and timing errors. Head-Fi, Nov 2021
• 2022-03-19Watts names three failings of conventional DACs: noise floor modulation (refinement, timbre), small signal accuracy (detail, depth) and transient timing (the WTA filter), then begins on noise. MFG Audio Reviews 5:10
• 2022-03-19Watts says small fixed noise is harmless, like concert-hall air conditioning, but noise rising with the music is noise floor modulation, which the brain cannot separate from the instrument. MFG Audio Reviews 5:54
• 2022-04-12Watts says the brain copes with harmonic distortion (cochlea about 4% THD) but not small signal distortion, noise floor modulation, anharmonic or timing errors, justifying -301dB accuracy. Head-Fi, Apr 2022
• 2022-10-12Watts says it creates harmonic and anharmonic distortion, calls the latter really nasty, and says only the WTA filter is designed to minimize these; the M Scaler adds computing power. Upscale Audio 3:50
• 2023-02-04Watts names three issues, small-signal accuracy, noise floor modulation and transient reconstruction (the most important), and begins explaining small-signal accuracy with a -100 dB signal. Dusty Audio 18:36
• 2023-03-28Watts lists distortion, small-signal nonlinearity, noise floor modulation and transient timing as factors in true transparency, saying timing errors are perceivable however small. The Headphone Show 40:09
• 2023-03-28Watts says higher-order and anharmonic distortion are big problems, and generally anything measurable has an audible consequence. The Headphone Show 40:57
• 2023-03-28Watts says DAVE's noise shapers going from 200 to 220 dB, and later 330 to 350 dB, improved depth; fixed noise is fine but signal-dependent noise creates noise floor modulation. The Headphone Show 44:02
• 2024-06-11Watts says the Mojo 2 HF filter's IIR phase change is linear and inaudible, unlike interpolation timing errors, and a listening test against an ADC-project FIR filter confirmed this. Head-Fi, Jun 2024
• 2024-07-12Watts names three main issues for ideal conversion: transients (interpolation filters, running at very high rates), small-signal accuracy (minus 301 dB), and a third. HIFICLUB 31:17
• 2026-05-03Watts says the saxophone then sounds brighter and artificial; timbre is also upset by transient timing, a technically different problem from supply-induced noise floor modulation. Audio Force 11:27
• 2026-05-03Watts says the brain compensates for harmonic distortion the ear itself creates, but noise floor modulation is not harmonically related: 20 Hz to 20 kHz noise changes with signal, brightening instruments. Audio Force 12:18
• 2026-10-02Watts says noisy, distorted 1930s mono recordings became enjoyable because the brain copes with natural analog distortion, as the ear itself is nonlinear, but not with digital's unnatural errors. HiFi Buys 26:02
• 2026-10-02Watts explains anharmonic distortion, at unrelated frequencies such as 1.2596 kilohertz rather than harmonics of the fundamental, which he says the brain cannot deal with because it does not occur naturally. HiFi Buys 39:45
• 2026-10-02Watts says noise per se does not matter: an acoustic guitar and saxophone would still sound fantastic in a room with air conditioning running. needs context HiFi Buys 51:52
• 2026-10-02Watts says noise on its own is really not important. HiFi Buys 52:15
• 2026-10-02Watts says it is when noise varies with the signal that it becomes a major issue. HiFi Buys 52:21
• 2026-10-02Watts says he is not bothered about phase, since a linear phase shift is in his experience inaudible. HiFi Buys 1:58:09
• 2026-10-02Watts says what matters is phase or transient timing that shifts with time, amplitude or the music; timing that is consistently wrong would not matter. HiFi Buys 1:58:18