Review and Measurements of SMSL SU-8 DAC

[SIY]

I agree. But as long as this DAC is used with volume control why worry about how it performs at 0dB or at -90dB as long as it performs good in between?

I would be interested to see THD+N at say -60dB, -40dB and -20dB as that is where this device will mostly be used. Don't you agree?

The reality is that the distortions here are unlikely to be audible. But I am somewhat esthetically bothered by engineering misses when it wouldn't have cost any more to get it right from end to end.

THD+N vs level at several frequencies is an interesting and often useful measurement. But again, we have to be ready to partition the results into D and N, as well as understand the nature of each.

I also am an advocate of multitone measurements- in my reviews, I use a 42 tone test signal.

 

[March Audio]

That doesn't explain it - unbalanced output doesn't suffer from clipping but has linearity issue.

Btw, clipping at 0dB is not an issue in my eyes as long as it works well at lower levels. As I said, I can't imagine anybody cranking the colume to 0 dB.

That depends upon how the dac is used. If you use it fixed volume into an amp with a volume control then the dac will often approach 0dB with many recordings. If, as I do, You use a software volume control and the dac directly feeds a power amp then the dac output is indeed reduced way below 0dB. - 15dB to - 25dB is a more typical level in my particular system.

You do have a point though, I too would like to see some intermediate levels tested.

 

[andreasmaaan]

The reality is that the distortions here are unlikely to be audible. But I am somewhat esthetically bothered by engineering misses when it wouldn't have cost any more to get it right from end to end.

THD+N vs level at several frequencies is an interesting and often useful measurement. But again, we have to be ready to partition the results into D and N, as well as understand the nature of each.

I also am an advocate of multitone measurements- in my reviews, I use a 42 tone test signal.

How is @amirm measuring IM to produce the graphs?

 

[Krunok]

You get a good view of this in the IMD test already posted by Amir. That is a test of IMD vs level.

Hmm.. THD and/or noise issues won't show on IMD graph.

 

[andreasmaaan]

Hmm.. THD and/or noise issues won't show on IMD graph.

There is a strong relationship between THD and IMD.

 

[Krunok]

That depends upon how the dac is used. If you use it fixed volume into an amp with a volume control then the dac will often approach 0dB with many recordings. If, as I do, You use a software volume control and the dac directly feeds a power amp then the dac output is indeed reduced way below 0dB.

I agree. But as this DAC has it's own digital volume control (which is supposed to be losless) and as most amps don't have volume control, in my eyes it would make sense to measure the performance at lower levels as well.

 

[March Audio]

There is a strong relationship between THD and IMD.

A direct relationship IIRC.

 

[Krunok]

There is a strong relationship between THD and IMD.

I don't think so. For example, harmonics generated from power supply and/or from USB packets won't show on IMD test.

 

[March Audio]

I don't think so. For example, harmonics generated from power supply and/or from USB packets won't show on IMD test.

Those are spuria and not signal related.

 

[Krunok]

Those are spuria and not signal related.

True, but it adds on both IM and harmonic distortion.

 

[andreasmaaan]

I don't think so. For example, harmonics generated from power supply and/or from USB packets won't show on IMD test.

True, that's why I said it's strongly related to THD, not THD+N (the power supply spuriae are not harmonically related to the signal and won't appear in any measurement of THD or IMD, but will appear in any measurement of THD+N).

It seems what you want to know is whether the power supply spuriae would stay at the same level if the signal were reduced to e.g. -60dBfs. Is that correct?

 

[Krunok]

How is @amirm measuring IM to produce the graphs?

Typically you fire 2 tones simultanously and measure what happens on the sum and the difference of their frequencies.

 

[andreasmaaan]

Typically you fire 2 tones simultanously and measure what happens on the sum and the difference of their frequencies.

Yeh, but there are many ways of doing this (not limited to just two-tone signals) and many standards for determining which harmonics are counted.

 

[March Audio]

True, but it adds on both IM and harmonic distortion.

No, it only would in thd + noise.

 

[Krunok]

It seems what you want to know is whether the power supply spuriae would stay at the same level if the signal were reduced to e.g. -60dBfs. Is that correct?

Yes, among other things. I also want to know what would happen to both, THD and THD+N at say -60dBfs.

 

[Krunok]

Yeh, but there are many ways of doing this (not limited to just two-tone signals) and many standards for determining which harmonics are counted.

You are not looking for harmonics when measuring IMD.

https://www.ap.com/technical-library/imd-vs-thdn/

 

[Krunok]

No, it only would in thd + noise.

I wanted to say that majority of the crap can be expressed as THD+IMD+different type of noise (harmonic signals from power supply and USB beeing some of them).

 

[andreasmaaan]

You are not looking for harmonics when measuring IMD.

https://www.ap.com/technical-library/imd-vs-thdn/

Yes you are, but you are looking at intermodulation harmonics. For example, the third order intermodulation harmonic specified in the CCIF standard is the harmonic that appears at frequencies 2*f1-f2 and 2*f2-f1.

 

[andreasmaaan]

Yes, among other things. I also want to know what would happen to both, THD and THD+N at say -60dBfs.

You can make a very confident prediction about THD at -60dBfs by looking at the IM graph. You can make an educated guess about THD+N by eyeballing the IM graph and then adding [100 (level of PS spuriae) + level (in -dBfs)] for the unbalanced outputs, or by adding [120 (level of PS spuriae) + level (in -dBfs)] for the balanced outputs.

 

[Krunok]

Yes you are, but you are looking at intermodulation harmonics. For example, the third order intermodulation harmonic specified in the CCIF standard is the harmonic that appears at frequencies 2*f1-f2 and 2*f2-f1.

Exactly. But I thought those are not called "harmonics".

Ok, let's be clear: if you send one tone that tone will be played along with its harmonics. If you play 2 tones those 2 tones are gonna be played along with their harmonics and with some new IM crap. If you play 3 tones those 3 tones will be played along with the harmonics of all 3 tones and some more IM crap. I believe we are all speaking of the same thing so let's not waste time on this.