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Article: Understanding Digital Audio Measurements

scott wurcer

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#61
I was referring to this post:
https://www.audiosciencereview.com/...-digital-audio-measurements.10523/post-292443

In fact I am completely fine with white noise and impulse response measurements, and any signal that can be stored in a specific file format.
There is at times IMO some confusion between "illegal input" and simply the image rejection of the reconstruction filter.

If you generate white noise at say 8x oversampling and use the inverse FFT to remove everything above 22050Hz there is nothing in the region just above fs/2 in the data.
 
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#62
I read much, but not all of the article. I might have missed the answer, but my question is:

If you have a 24bit audio stream and are playing it on a DAC that is capable of say 19 bits of range, are you missing the quietest parts(they're cut off from the stream), or is it compressed such that there is not as many dBs between the loudest vs quietest? Thank you.
 

trl

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#63
The 24bit audio is the digital representation of the song, while the "19 bits of range" is the actual signal-over-noise (SINAD). SINAD is influenced a lot by the analog parts from the audio chain, because electronic components are adding noise and distortions over the original sound, but also the jitter and digital artefacts could affect the final SINAD as well.

I would personally don't try to compare the SINAD with the bitrate of the audio files.

For me, if the audio chain I'm listening to has a SINAD of at least 16-bits on the listening levels (e.g.: equivalent of an AVG 85dB for both headphones and speakers) then I would be very pleased.
 
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amirm

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Thread Starter #64
I read much, but not all of the article. I might have missed the answer, but my question is:

If you have a 24bit audio stream and are playing it on a DAC that is capable of say 19 bits of range, are you missing the quietest parts(they're cut off from the stream), or is it compressed such that there is not as many dBs between the loudest vs quietest? Thank you.
You are. But the limit of capture and reproduction in audio is about 20 to 21 bits. It is very unlikely that you have that much useful information in recorded music as noise takes over the low order bits. So 19 bits is fine too.

And no, nothing is compressed. If SINAD is higher, then you are stepping on any music bits with either noise, distortion or both created by the DAC.
 

pozz

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#65
I read much, but not all of the article. I might have missed the answer, but my question is:

If you have a 24bit audio stream and are playing it on a DAC that is capable of say 19 bits of range, are you missing the quietest parts(they're cut off from the stream), or is it compressed such that there is not as many dBs between the loudest vs quietest? Thank you.
If you have a DAW or an editing program try playing a track at regular volume and then lowering it by 80dB (~13 bits, or well within CD range). You will likely hear nothing.

But to answer your question. 19 bits or ~114dB of range will has to be defined. Linearity, SINAD, SNR or DAC capability?
  • 114dB linearity means that signals below this level will not be produced with the correct volume. The values will be unstable and fluctuate randomly.
  • 114dB SINAD means that below this level either noise or distortion will begin to play along with the music.
  • 114dB SNR is the same as the above, but ignoring distortion (which is usually above the noise floor of the DAC).
  • 114dB of DAC capability means that the DAC will cut any signal below this level out entirely. I think one or two measured units had this problem.
 
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#66
If you have a DAW or an editing program try playing a track at regular volume and then lowering it by 80dB (~13 bits, or well within CD range). You will likely hear nothing.

But to answer your question. 19 bits or ~114dB of range will has to be defined. Linearity, SINAD, SNR or DAC capability?
  • 114dB linearity means that signals below this level will not be produced with the correct volume. The values will be unstable and fluctuate randomly.
  • 114dB SINAD means that below this level either noise or distortion will begin to play along with the music.
  • 114dB SNR is the same as the above, but ignoring distortion (which is usually above the noise floor of the DAC).
  • 114dB of DAC capability means that the DAC will cut any signal below this level out entirely. I think one or two measured units had this problem.
Thank you for the details. How about in the case of the latest review, here (Topping E30). What definition, above, would the 19.5bits fall under?
 
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#67
The 24bit audio is the digital representation of the song, while the "19 bits of range" is the actual signal-over-noise (SINAD). SINAD is influenced a lot by the analog parts from the audio chain, because electronic component are adding noise and distortions over the original sound, but also the jitter and digital artefacts could affect the final SINAD as well.

I would personally don't try to compare the SINAD with the bitrate of the audio files.

For me, if the audio chain I'm listening to has a SINAD of at least 16-bits on the listening levels (e.g.: equivalent of an AVG 85dB for both headphones and speakers) then I would be very pleased.
Thank you. How would you go about measuring the bits/dBs/dynamic range of the entire system? How would you know what you're missing?
 

pozz

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#68
Thank you for the details. How about in the case of the latest review, here (Topping E30). What definition, above, would the 19.5bits fall under?
1 bit is approximately 6.02 dB. So 19.5 bits is 117dB. Keep in mind what Amir said about the absolute noise floor being 20-21bits for all electronics. It's an unbreakable limit at the moment, quantum computing excluded.
 

trl

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#69
Thank you. How would you go about measuring the bits/dBs/dynamic range of the entire system? How would you know what you're missing?
https://www.audiosciencereview.com/...om-measurement-tutorial-for-dummies-part-1.4/
https://www.audiosciencereview.com/...om-measurement-tutorial-for-dummies-part-2.5/
https://www.audiosciencereview.com/...om-measurements-plots-and-help-with-rew.8601/

The most important things to measure on your audio system:
  1. Get a song with a good dynamic and pump up the volume when it reaches that level of audio energy that pleases you most (you can optionally measure the output dB from the listening position, if you want);
  2. Listen to your room, see what resonates most, search for reverberations, then find a way to damp and absorb those unwanted sounds (use at least a minimum treatment for your room);
  3. Turn off the music, leave the volume knob at the same position from step 1, take a 5 min. break so your ears to accommodate with room silence, then from the listening position try to identify if mains hum or hiss noise can be audible coming from your speakers.
If on step 2 you don't hear your room "vibrating" and on step 3 you can't hear any noise or hum, I guess there is no subjective reason to make any upgrade.

Of course, REW & a calibration mic would help a lot here, so you can better check and understand if there's something wrong with your audio system or not.
 

wwenze

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#70
"Multitone Testing
An incorrect criticism against audio measurements is that we usually use a single tone and hence the result can’t possibly apply to music, which has countless tones. The argument misses the case that if a DAC distorts one tone, it will just as well distort one thousand. Anyway, to deal with the criticism, we can run more tones."

A recent few DACs measured have shown not 100% correlation between SINAD and multitone so I guess there is worth.

One thing I noticed however is that the "grass" of the Okto used in this article is much lower than the harmonic distortion components. That's when I realized the 32 tones themselves are harmonics of each other so we won't see harmonic distortion.

I'm wondering should we offset the tones' frequencies so they no longer hide harmonic distortion, then we can see a graph that contains both.
 

RayDunzl

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#71
That's when I realized the 32 tones themselves are harmonics of each other so we won't see harmonic distortion.
I believe the tone frequencies have logarithmic spacing.

1585205461099.png


For example, there appears to be a tone at 100Hz. There is no tone at 300Hz, the third harmonic.

Harmonics are integer multiples of a fundamental.

Some may overlap, but not all.
 

Schackmannen

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#72
"Multitone Testing
An incorrect criticism against audio measurements is that we usually use a single tone and hence the result can’t possibly apply to music, which has countless tones. The argument misses the case that if a DAC distorts one tone, it will just as well distort one thousand. Anyway, to deal with the criticism, we can run more tones."

A recent few DACs measured have shown not 100% correlation between SINAD and multitone so I guess there is worth.

One thing I noticed however is that the "grass" of the Okto used in this article is much lower than the harmonic distortion components. That's when I realized the 32 tones themselves are harmonics of each other so we won't see harmonic distortion.

I'm wondering should we offset the tones' frequencies so they no longer hide harmonic distortion, then we can see a graph that contains both.
Amir has posted the multitone test file before and IIRC the tones are generated so that none of them are an integer multiple of the others so harmonic distortion still show up in the test. I think the reason why the distortion sometimes looks lower in the multitone test than in the dashboard is because each tone in the multitone test has to be a lower amplitude than the single tone in the dashboard, otherwise they would sum up to over 0 dBFS and clip, which means that the distortion created by each tone in the multitone test is a lot lower in amplitude.
 

RayDunzl

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#73
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JimB

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#74
Sorry if this has already been addressed somewhere on the site, but it struck me (red emphasis, mine):

AKM's two-chip DAC solution that separates the digital aspect from the analog was announced following a period of extensive tests promoted by the Japanese company using controlled listening tests. The results, as the company notes, validated the combination of the AK4191 premium delta-sigma modulator with multi-bit output chip for enhanced digital signal processing capability, when combined with with the AK4498 premium D/A converter with multi-bit modulator data interface, resulting in superior dynamic with vast playback resolution, as well as improved noise immunity and increased low-frequency noise performance.

AKM is now offering this solution for the audio industry, recommending the two-chip solution for high-end audio designs, active speakers, network audio and USB DAC applications. "By using two ICs, AKM has minimized the effects of digital noise within the analog output, resulting in a perceived improvement of the ratio of signal to noise. This improvement, while not easily quantifiable via traditional measurement techniques, is easily experienced during controlled listening tests," the company states.
 

pozz

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#75
Sorry if this has already been addressed somewhere on the site, but it struck me (red emphasis, mine):

AKM's two-chip DAC solution that separates the digital aspect from the analog was announced following a period of extensive tests promoted by the Japanese company using controlled listening tests. The results, as the company notes, validated the combination of the AK4191 premium delta-sigma modulator with multi-bit output chip for enhanced digital signal processing capability, when combined with with the AK4498 premium D/A converter with multi-bit modulator data interface, resulting in superior dynamic with vast playback resolution, as well as improved noise immunity and increased low-frequency noise performance.

AKM is now offering this solution for the audio industry, recommending the two-chip solution for high-end audio designs, active speakers, network audio and USB DAC applications. "By using two ICs, AKM has minimized the effects of digital noise within the analog output, resulting in a perceived improvement of the ratio of signal to noise. This improvement, while not easily quantifiable via traditional measurement techniques, is easily experienced during controlled listening tests," the company states.
Details from the company would be definitely interesting.
 
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