Should digital headroom for DACs and DSPs be tested as part of review measurements?

[bennetng]

If you want a test signal with audible artifacts when ISOs are clipped you can try one proposed by bennetng:
(note: it contains high level 18 kHz tone)

Let's develop an ASR inter-sample test procedure for DACs!

Here we go. I did 2 passes. First pass scoring 9/10, taking time to get familiar with the tracks; then a second pass scoring 10/10, during which I was faster. In this instance, it was all about the transient. The reference track has more energy at that peak you're showing in your graph...

www.audiosciencereview.com

Discussed first here:

Invitation: Audible intersample clipping test

The test signal is attached at the end of this post: https://forum.cockos.com/showthread.php?t=201868 Basically I don't like the idea of blaming those who make music or DACs for intersample clipping since there is no absolute clipping point. My test signal is a bit more sophisticated than the...

www.audiosciencereview.com

Thanks for linking to my posts. I'd add another one which is not a crafted test signal but from a published CD. I reposted this several times on ASR but it got ignored. In subsequent replies two members claimed they can hear the distortion and posted ABX results, even though I myself cannot hear the difference.

Let's develop an ASR inter-sample test procedure for DACs!

Source: https://www.sfu.ca/sonic-studio-webdav/cmns/Handbook Tutorial/Audiology.html Thanks for reminding this book! Assuming that music has similar effect like noise, after 15 minutes of listening at 85dB SPL average, we will temporarily lose ability to hear noise at 8dB SPL. Does nature abhor...

www.audiosciencereview.com

Last year I also posted an article somewhat related to intersample over. Near the end of the article I posted some Stereophile measurement screenshots. To avoid causing troubles to Archimago I did not expose the names of the products in the article. Can anyone guess which DAC produced artifacts in the -90dB test?

Another Digital Volume Control Article (Guest post by Bennet Ng)

A blog for audiophiles about more objective topics. Measurements of audio gear. Reasonable, realistic, no snakeoil assessment of sound, and equipment.

archimago.blogspot.com

 

[popej]

Sending such signal (8800+11000+17640Hz), even without clipping, is just good to destroy the tweeters.

It is a test only. Amir routinely performs full power test of amplifiers at 15kHz.
Sure, I wouldn't run it with speakers.

 

[KSTR]

If Amir could be persuaded to test for this in the future the next question would be whether it would be just one simple test and consider that pass or fail and how much ISO would that be or should Amir do more elaborate testing exploring the max. headroom a DAC has (which could perhaps be done with one test as well ?)

Looking at the +3dBTP fs/4 signal in time domain, using the steepest filter (the closer to true sinc the larger the ISOs) allows for a quick check with like three types of output:

• visibly unclipped/undistorted and uniform over time : best case ("excellent").
• visibly clipped tops and bottoms of the waveform, but otherwise uniform : benign ISO artifacts ("fair"), most likely inaudble most of the time
• fold-over, wrap-around, or anything not uniform over time (like that Pioneer DJ player's weird output) : strong ISO artifacts ("bad"), quite likely audible in some cases

 

[solderdude]

The difficult part is to convince Amir he should do that for all future DAC tests.
The difficulty is not the test itself nor the reporting of it.

What perhaps could help persuade him is some scope shots of a few DACs of the same type he has already tested and showing some do this well and others don't.

 

[bennetng]

Looking at the +3dBTP fs/4 signal in time domain, using the steepest filter (the closer to true sinc the larger the ISOs) allows for a quick check with like three types of output:

• visibly unclipped/undistorted and uniform over time : best case ("excellent").
• visibly clipped tops and bottoms of the waveform, but otherwise uniform : benign ISO artifacts ("fair"), most likely inaudble most of the time
• fold-over, wrap-around, or anything not uniform over time (like that Pioneer DJ player's weird output) : strong ISO artifacts ("bad"), quite likely audible in some cases

While the ultimate solution is to use software volume control/management, if I have to test hardware devices, I would check if the the hardware volume control on the device (if available) can deal with the overs or not instead of simply use max/fixed output and give a judgment.

 

[Davey2156]

The difficult part is to convince Amir he should do that for all future DAC tests.
The difficulty is not the test itself nor the reporting of it.

What perhaps could help persuade him is some scope shots of a few DACs of the same type he has already tested and showing some do this well and others don't.

Amir is already on record (numerous times, and even in this thread) saying he doesn't believe this is a worthwhile test for him to run when testing DAC's.
There's no need to continue to prod him.
John Siau finally threw his hands up and left the forum.

Time to move on.

 

[John_Siau]

Amir is already on record (numerous times, and even in this thread) saying he doesn't believe this is a worthwhile test for him to run when testing DAC's.
There's no need to continue to prod him.
John Siau finally threw his hands up and left the forum.

Time to move on.

No, I'm still here reading these comments.

The basic concept is this:

A DAC should be able to play existing CD tracks without overloading.

 

[John_Siau]

With the +3 dBFS 11.025 kHz test tone there are at least four common test results:

1) The sine wave plays cleanly. - Best
2) The sine wave is clipped but the distortion is purely harmonic. - Marginal
3) The sine wave is clipped and there is significant in-band IMD. - Bad
4) The overs create a DSP wraparound error. - Egregious

Examples of the above:

1) Benchmark DAC2, DAC3, Oppo UDP-205 and some others
2) Topping E50 (see post #56 of this thread), Marantz SA7001 (see post #54), RME ADI-2 Pro FS
3) Benchmark DAC1 and many others including Pioneer CDJ-2000NXS2 (see post #56)
4) Yamaha CDX-596 (see post #44), Denofrips Pontus 2 (acording to Goldensound), and some others

Audibility:

1) Transparent (no added distortion or noise)
2) Inaudible distortion (mostly above 20 kHz), may cause issues for tweeters and power amplifiers in extreme cases
3) Loud enough to be audible in some circumstances
4) Very audible

We need to test because some new products still fall into categories 3 and 4. Some products in categories 3 and 4 will play cleanly when their volume controls are turned down. Others from categories 3 and 4 will stay distorted when their volume controls are turned down.

Without testing, the consumer has no clue which of these 4 categories a DAC will fall into.

 

[pma]

What perhaps could help persuade him is some scope shots of a few DACs of the same type he has already tested and showing some do this well and others don't.

Are you still naive?

 

[solderdude]

Are you still naive ?

Optimistic

 

[pma]

I did try some practical example. 11025Hz Fs/4, 45deg, +2dBFS test sine, Marantz SA7001 CDP + Topping DX5 DAC via Toslink, and mediocre class D amplifier BerryBak2300, see my review. The volume pot of the DX5 was set to some -8dBFS.

The output spectrum looks more than normal, with respect to regular set of measurements of this amplifier. Only ultrasound components + usual low level mess, typical for this amp.

Regular THD+N measurement at 11025 Hz and 125W/4R7 says -53.6dB, more or less the same value. So the "unusual signal" brought nothing. And with volume pot at 0dBFS we would be at hard hard amplifier clipping.

 

[pma]

With the +3 dBFS 11.025 kHz test tone there are at least four common test results:

1) The sine wave plays cleanly. - Best

Do not send it to the speaker to see if it "plays cleanly". You might destroy both tweeters and your ears, the "fired spots" in the inner ear.

 

[Loomynarty]

The Pontus 2 did the same, but I think that (the wrap around) is more of an implementation problem more than anything else. I think Denfarips corrected this via a firmware update.

When I had an Ares II, it also had this problem. Vinshine sent me a firmware update that was supposed to fix it but it never did. I sold the DAC because of this and I will never recommend buying a Denafrips DAC to anyone. ISO's should be a non-issue for any DAC made in the last 20 years and it's frankly embarrassing that Denafrips can't fix it.

The issue is so bad I remember throwing my headphones off my head once because of the sound the ISO caused the DAC to emit.