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Review: Battle of Schiit Audio DACs

amirm

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#61
I think the comboburrito filter doesnt work at 192khz as I understand it. The DAC goes into some kind of nos mode at that point. It only works up to 96khz and below. WOuld be interesting to see how a sample rate below 192khz does.
OK, as promised here is the filter response at 44.1 kHz:

Schiit Modi 2 Multibit DAC Filter Response at 44100 Measurements.png


As expected from a high-tap filter, the Modi Multibit has sharper and flatter response than whatever they are using in Modi 3. However, its attenuation of ultrasonics is much less (70 dB versus nearly 100 dB for Modi 3).
 

amirm

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#62
In my DAC reviews, I am testing for "macro effects." That is, how the system as a whole operates. I don't dig into intricacies of the DAC chips themselves as they are so proven these days that the issues are mostly all in implementation.

Here though, Schiit uses a DAC chip not designed for audio so I thought I dig in and see if I can find any corner cases. As luck would happen, I immediately found a "micro" issue with any input signal that is a multiple of 100 Hz. Here, I show what happens when you feed the DAC initially 9999 Hz and then 10,000 Hz:
Schiit Modi Multibit DAC 100 Hz signal processing problem Measurements.png


The moment you click up the frequency one Hz to 10,000, you see distinct pattern of 100 Hz components across the full spectrum. Further, the noise floor goes down, making them appear more easily.

I tested this up to 192 Khz and it is there at all sample rates so it is not the Schiit filter. It must be inherent to the design of the Analog Design DAC.

To test this further, I changed the tone to -60 dB and got this:
Schiit Modi Multibit DAC 100 Hz -60 dB signal processing problem Measurements.png


Problem remains but frequency of the extra tones changes. The amplitude of distortion components does not change which means now they are only 60 dB lower than our main tone (rather than 120 before). So perhaps at the extreme this an audible concern. You have a form of dynamic distortion that only plagues certain audio samples in your music and not others.

Same test on Schiit Modi 3 shows no such issue.

There is a cost to ignoring 30 years of progress in DAC design and going with odd choices of silicon as is the case here. Carefully measuring prototype designs for such glitches should have been performed before deciding to proceed.

Anyway, we are deep in measurebating but I thought I share this. :)

Edit: lost a bit of text in the original post which I added back in.
 
Last edited:

Jimster480

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#63
Awesome find,
I think that all of this adds up to the loss of detail that I heard when using the Modi Multibit vs even my D30 at the time or the SMSL M8 I got around the same time.
 

gvl

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#64
Interesting, how big of a SINAD improvement you get if you test say at 999Hz instead of 1kHz?
 

amirm

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#65
Interesting, how big of a SINAD improvement you get if you test say at 999Hz instead of 1kHz?
Nothing. The main harmonic distortions are so high that these become round off errors.
 

gvl

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#66
I know of one company that's pushing multibit tech that originally used industrial chips in their designs but eventually developed their own ladder DAC modules citing they couldn't get the desired audio performance from the industrial silicon.
 

garbulky

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#67
In my DAC reviews, I am testing for "macro effects." That is, how the system as a whole operates. I don't dig into intricacies of the DAC chips themselves as they are so proven these days that the issues are mostly all in implementation.

Here though, Schiit uses a DAC chip not designed for audio so I thought I dig in and see if I can find any corner cases. As luck would happen, I immediately found a "micro" issue with any input signal that is a multiple of 100 Hz. Here, I show what happens when you feed the DAC initially 9999 Hz and then 10,000 Hz:
View attachment 18322

The moment you click up the frequency one Hz to 10,000, you see distinct pattern of 100 Hz components across the full spectrum. Further, the noise floor goes down, making them appear more easily.

I tested this up to 192 Khz and it is there at all sample rates so it is not the Schiit filter. It must be inherent to the design of the Analog Design DAC.

To test this further, I changed the tone to -60 dB and got this:
View attachment 18325

Problem remains but frequency of the extra tones changes. The amplitude of distortion components does not change which means now they are only 60 dB lower than our main tone (rather than 120 before). So perhaps at the extreme this an audible concern. You have a form of dynamic distortion that only plagues certain audio samples in your music and not others.

Same test on Schiit Modi 3 shows no such issue.

There is a cost to ignoring 30 years of progress in DAC design and going with odd choices of silicon as is the case here. Carefully measuring prototype designs for such glitches should have been performed before deciding to proceed.

Anyway, we are deep in measurebating but I thought I share this. :)

Edit: lost a bit of text in the original post which I added back in.
Of more importance than finding -120 db spurious tone is the -65 db (?) tone appearing on the 0 db signal during that 100 hz multiple at 20 khz. Granted it's at 20 khz so ears like a bat and all that. But it's still -65 db.
 

amirm

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#68
Of more importance than finding -120 db spurious tone is the -65 db (?) tone appearing on the 0 db signal during that 100 hz multiple at 20 khz.
20 Khz is 2nd harmonic of 10 kHz main input signal so it is normal for it to be there. It is not a spurious response.
 

gvl

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#69
Dashboard shows 2nd harmonic at -85dB. Did you capture a THD vs. frequency that I missed?
 

amirm

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#70
Dashboard shows 2nd harmonic at -85dB. Did you capture a THD vs. frequency that I missed?
I didn't. I will be on the road tomorrow making deliveries and picking up gear for review. Will probably be back Tuesday and can run the test then.
 

Blumlein 88

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#71
I didn't. I will be on the road tomorrow making deliveries and picking up gear for review. Will probably be back Tuesday and can run the test then.
Here is an idea. Paint the camper van brown. Write UPS on the side. Pick up Christmas gear for review and leave a note saying it is back ordered. Test and return. Hey, you are just providing an extra step of free QC.

Or I think Schiit should pay you a stipend for the work you are doing for them. Just don't let them swap it out in Schiit gear.
 

amirm

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#72
Paint it brown? The van is white so can be used instantly as a FedEx delivery van. Indeed my retirement plan is to use it for that to make some extra money!!!
 
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#73
OK, as promised here is the filter response at 44.1 kHz:

View attachment 18321

As expected from a high-tap filter, the Modi Multibit has sharper and flatter response than whatever they are using in Modi 3. However, its attenuation of ultrasonics is much less (70 dB versus nearly 100 dB for Modi 3).

Thank you for your work! Guess the digital filter doesnt have any audible effect then, unless you are playing music for dogs.
 
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#75
Just wanted to chime in and say that thanks to this forum, I didn’t buy the Modi Multibit and went with another option, specifically the Topping DX3 Pro

If I didn’t see this forum I would’ve ended up buying the Modi Multibit and wasting my hard earned money, I was actually considering it for my new DAC
 
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