Hello,
I would like to make a suggestion that DAC reviews included PCM filters responses charts, not only for single-speed sampling rates (44.1khz, 48khz) but also for double-speed (88.2khz and/or 96khz).
The reason is that it seems that for some DACs, the filters' responses and efficiency are dependent on the input sampling rates.
A PCM filter that does -110db attenuation at 48khz, could well have only -80db attenuation at 96khz... and these figures would not appear on the DAC's data sheet, because the maker only publishes measurements at single speeds.
For instance, for the Cirrus CS43198 chip (used in Topping D70 Pro Octo), the built-in PCM filters seem to have a different behavior under different input PCM sampling rates.
In the Cirrus Data Sheet ( CS43198_DS1156F2.pdf ) :
- p16: Fast Roll-Off (FILTER_SLOW_FASTB = 0) Single-Speed Mode 1 : Stopband attenuation 6 110
- p17: Fast Roll-Off (FILTER_SLOW_FASTB = 0) Double-Speed Mode 1 : Stopband attenuation 6 80
So at "double speed" (96khz), the filter attenuation seems to be only -80db as compared with "single speed" where it is at -110db : this is a 30db performance difference, and there might be concerns here because this lower attenuation might introduce artifacts in the signal (including into the audible bandwidth, see comment below).
Indeed, I found interesting comments about such DAC behavior from Benchmark's John Siau, so I will cite them here (he is comparing double- to quad- speeds, but the same remarks are applicable for single- to double- in the example above), from ( forum.psaudio.com/t/96khz-vs-192khz-2012-statement-from-john-siau/25832 ) :
Came across this old 2012 statement from Benchmark VP John Siau regarding 96kHz and 192kHz. Is this info outdated and not applicable to most current DACs?
All of Benchmark’s A/D converters and D/A converters support sample rates up to 192kHz. However, we strongly recommend 96kHz for optimum performance. There is a performance penalty for operating at 192kHz. The problem is that all A/D and D/A converter chips operate at reduced oversampling ratios when converting at 192kHz. At the current time, the negative consequences of the reduced oversampling ratio far outweigh any benefits derived from the higher sample rates.
At 192kHz the stopband attenuation of the digital filters is usually much poorer than at 96kHz. Many converter ICs have 120dB of stopband attenuation at 96kHz, but only 80dB at 192kHz. This makes 192kHz converters very susceptible to aliasing and poor image rejection. These artifacts clutter the audible spectrum with low-level non-musical distortion.
It can be shown and demonstrated that there is no loss of time-domain accuracy when operating at 96kHz versus 192kHz. It is a myth that 192kHz gives better time-domain accuracy.
To date, Benchmark has no evidence that 192kHz performs better than 96kHz, but we have a substantial body of evidence that shows that 192kHz has defects that are not present at 96kHz. These issues are also shared openly by one of our competitors: Lavry Engineering. We suspect many other manufacturers are aware of these issues, but choose not to talk about them.
Bottom line: Be very careful about any claims that 192kHz sounds better than 96kHz. Our experience points in the opposite direction.
John Siau
V.P., Benchmark Media Systems, Inc.
This would surely help identifying DACs that have good PCM filtering management accross all sampling rates, and not only at single speeds.
What do you think about this?
I would like to make a suggestion that DAC reviews included PCM filters responses charts, not only for single-speed sampling rates (44.1khz, 48khz) but also for double-speed (88.2khz and/or 96khz).
The reason is that it seems that for some DACs, the filters' responses and efficiency are dependent on the input sampling rates.
A PCM filter that does -110db attenuation at 48khz, could well have only -80db attenuation at 96khz... and these figures would not appear on the DAC's data sheet, because the maker only publishes measurements at single speeds.
For instance, for the Cirrus CS43198 chip (used in Topping D70 Pro Octo), the built-in PCM filters seem to have a different behavior under different input PCM sampling rates.
In the Cirrus Data Sheet ( CS43198_DS1156F2.pdf ) :
- p16: Fast Roll-Off (FILTER_SLOW_FASTB = 0) Single-Speed Mode 1 : Stopband attenuation 6 110
- p17: Fast Roll-Off (FILTER_SLOW_FASTB = 0) Double-Speed Mode 1 : Stopband attenuation 6 80
So at "double speed" (96khz), the filter attenuation seems to be only -80db as compared with "single speed" where it is at -110db : this is a 30db performance difference, and there might be concerns here because this lower attenuation might introduce artifacts in the signal (including into the audible bandwidth, see comment below).
Indeed, I found interesting comments about such DAC behavior from Benchmark's John Siau, so I will cite them here (he is comparing double- to quad- speeds, but the same remarks are applicable for single- to double- in the example above), from ( forum.psaudio.com/t/96khz-vs-192khz-2012-statement-from-john-siau/25832 ) :
Came across this old 2012 statement from Benchmark VP John Siau regarding 96kHz and 192kHz. Is this info outdated and not applicable to most current DACs?
All of Benchmark’s A/D converters and D/A converters support sample rates up to 192kHz. However, we strongly recommend 96kHz for optimum performance. There is a performance penalty for operating at 192kHz. The problem is that all A/D and D/A converter chips operate at reduced oversampling ratios when converting at 192kHz. At the current time, the negative consequences of the reduced oversampling ratio far outweigh any benefits derived from the higher sample rates.
At 192kHz the stopband attenuation of the digital filters is usually much poorer than at 96kHz. Many converter ICs have 120dB of stopband attenuation at 96kHz, but only 80dB at 192kHz. This makes 192kHz converters very susceptible to aliasing and poor image rejection. These artifacts clutter the audible spectrum with low-level non-musical distortion.
It can be shown and demonstrated that there is no loss of time-domain accuracy when operating at 96kHz versus 192kHz. It is a myth that 192kHz gives better time-domain accuracy.
To date, Benchmark has no evidence that 192kHz performs better than 96kHz, but we have a substantial body of evidence that shows that 192kHz has defects that are not present at 96kHz. These issues are also shared openly by one of our competitors: Lavry Engineering. We suspect many other manufacturers are aware of these issues, but choose not to talk about them.
Bottom line: Be very careful about any claims that 192kHz sounds better than 96kHz. Our experience points in the opposite direction.
John Siau
V.P., Benchmark Media Systems, Inc.
This would surely help identifying DACs that have good PCM filtering management accross all sampling rates, and not only at single speeds.
What do you think about this?
