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Does MOTU M2 cut frequencies at 20kHz when used as a DAC?

cestx

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I decided to buy a pair of Genelecs 8030C (a great tip received in this forum) and now I am looking for a suitable DAC to connect them to a laptop. As I am listening to flac files, I need the DAC to fairly reproduce all frequencies in the range 20Hz-26kHz. MOTU M2 was recommended to me by a local dealer. I practically decided to order M2 but then noticed that its user manual states that its frequency response is only "20Hz-20kHz (plus minus 0.1 db)". Does it mean that MOTU M2, when used as a DAC, cuts off frequencies beyond 20kHz?
 

voodooless

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No, it does not:
1657390827824.png


See:


You’ll need a unhumanly pair of ears though to hear 26 kHz, and material recorded at more than 48 kHz.

The 8030C also does 25 kHz at -6 dB so 26 will be lower.

Why worry about it?
 

dc655321

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Does it mean that MOTU M2, when used as a DAC, cuts off frequencies beyond 20kHz?

Not quite. See here.
Chances are good you can’t hear up to 20kHz and most content has very little energy up there either.
 

voodooless

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That's the input, not the the output.
I agree though. The M2's Line out should easily extend to 40K and beyond. Still, would be nice to have a graph.
Ah, your right! No reason to think the output is limited though.
 
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cestx

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Why worry about it?
After listening to quite a few recordings I convinced myself that the same recording with frequencies exceeding 20kHz filtered out sounds worse. I haven't noticed any decrease of quality after removing frequencies exceeding 26kHz. Of course, this also depends on the recorded material. For example, piano solo sounds fine to me even after cutting off frequencies beyond 15kHz.
 
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cestx

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Ah, your right! No reason to think the output is limited though.
Please, forgive a total dummy in this sort of technology, but is there a reason to think otherwise, i.e. that the output extends beyond 20kHz and not sharply falls as in some graphs in the aforementioned review?
 

voodooless

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After listening to quite a few recordings I convinced myself that the same recording with frequencies exceeding 20kHz filtered out sounds worse.
Better ABX this!
Please, forgive a total dummy in this sort of technology, but is there a reason to think otherwise, i.e. that the output extends beyond 20kHz and not sharply falls as in some graphs in the aforementioned review?
There really is no reason to think so. Modern interfaces have wide frequency response. You just need a sample rate that supports the bandwidth. The reason you see the falloff in the review is the used sample rate for the test (44.1 kHz). This is how it should be.
 

DVDdoug

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The ASR review shows up to 84kHz with a sample rate of 192kHz.

In case you don't know this, you are limited (by "math") to half of the sample rate (Nyquist theory). This is logical since you need at-least one sample for the positive-half of the waveform and another sample for the negative-half, So, CDs (at 44.1kHz) can't contain anything over 22,050Hz. In practice there are (imperfect) filters so you can't go all the way to 22,050 with a CD. If you "try" to go higher (without properly filtering) you get aliasing... Additional lower-frequencies that weren't in the original.

At higher sampling rates you don't always get higher audio capability because audio interfaces are made for audio, and ultrasonics may be filtered out just as "good practice", or so they can use the same filter for all sample rates.

After listening to quite a few recordings I convinced myself that the same recording with frequencies exceeding 20kHz filtered out sounds worse.
Either there is "something wrong" with your filter, or maybe you are fooling yourself. It's easy to fool yourself unless you do a proper, level-matched, scientific, ABX Test.

It turns out that even if you can hear up to 20KHz in a hearing test with "loud" test tones, when you're listening to music, the highest frequencies (which are harmonics, not "musical notes") are weak and masked (drowned-out) by stronger and slightly lower frequencies.

And as long as there isn't some kind of unusual intermodulation distortion, the ultrasonic frequencies have no effect on what you're actually hearing down in the audio range.

P.S.
Filter cut-off is defined as the -3dB point,
no matter how sharp the filter. So a 20kHz low-pass filter is 3dB down at 20kHz and a 15kHz filter is 3dB down at 15kHz. If you want flat audio at 20kHz a low-pass filter needs a higher cutoff frequency,
 
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cestx

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Better ABX this!
Yes, I am aware that 20Hz-20kHz is called "an audible range". However, there is also the observation stated above which I made for myself. In fact, I made it before I learned about lossless audio formats and that was how I started listening to flacs: the presence of past-20kHz frequencies became an important a priori criterion for me which was confirmed on several occasions in a kind of blind tests.
 

sarumbear

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I decided to buy a pair of Genelecs 8030C (a great tip received in this forum) and now I am looking for a suitable DAC to connect them to a laptop. As I am listening to flac files, I need the DAC to fairly reproduce all frequencies in the range 20Hz-26kHz. MOTU M2 was recommended to me by a local dealer. I practically decided to order M2 but then noticed that its user manual states that its frequency response is only "20Hz-20kHz (plus minus 0.1 db)". Does it mean that MOTU M2, when used as a DAC, cuts off frequencies beyond 20kHz?
20Hz-20kHz (plus minus 0.1 db) is the linearity of the FR, not the bandwidth. Bandwidth would have been -3dB.

M2 can process 192kHz sampled digital signal. This means it’s bandwidth is at least extends to 96kHz, the Nyqvist frequency.
 

bennetng

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Does it mean that MOTU M2, when used as a DAC, cuts off frequencies beyond 20kHz?
Highly unlikely. Even crabby Realtek chips these days have pretty flat frequency response beyond 26kHz when operating at 96kHz or higher.

96k loopback
fr.png


192k loopback
192fr.png


Detailed reports are attached in this post:

The 20Hz-20kHz 0.1dB things are just the measurement range, doesn't mean there is nothing below 20Hz and above 20kHz.

Of course, if you are really paranoid, better wait for some of the M2 owners posting their own results.
 
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staticV3

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The ASR review shows up to 84kHz with a sample rate of 192kHz
That's the analog input, not the analog output, which OP is asking about. That was not tested in Amir's review.

M2 can process 192kHz sampled digital signal. This means it’s bandwidth is at least extends to 96kHz, the Nyqvist frequency.
No. Support for 192kHz sample rate content does not guarantee 96kHz bandwidth of the analog output.

For example, the Meizu HiFi can play back up to 32/384 content, but the bandwidth of it's analog output stops well short of Nyquist. It can't even play back 192kHz content in its entirety:
Meizu HiFi Frequency Response.png
 
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sarumbear

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No. Support for 192kHz sample rate content does not guarantee 96kHz bandwidth of the analog output.
I cannot believe that a DAC manufacturer offers 192kHz sampling rate on a product that does not satisfy Nyquist?
 

Blumlein 88

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Yes, but that graph is in the part where M2 is tested as an ADC but I will use it as a DAC.
So maybe someone here with an M2 could do a loopback measurement at 192 khz. We know it has response on the ADC side, if the loopback is good then the DAC must work at those frequencies too.

And yes, something down -.1 db at 20 khz is typically down about -3 db around 200 khz. So I don't think it is a stretch to think it is good to 26 khz at least.
 

Blumlein 88

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I cannot believe that a DAC manufacturer offers 192kHz sampling rate on a product that does not satisfy Nyquist?
Some do intentionally like Lavry. However those I've seen do this have response to 35-40 khz before intentionally rolling it off.
 

staticV3

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I cannot believe that a DAC manufacturer offers 192kHz sampling rate on a product that does not satisfy Nyquist?
I doubt that even half of the DACs on sale today can hit Nyquist at their max sample rate.
 

sarumbear

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I doubt that even half of the DACs on sale today can hit Nyquist at their max sample rate.
Really? What is the limitation they face? Surely a 100kHz audio signal path is not a problem.
 

bennetng

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Another loopback example from RME and Benchmark:
index.php


Not really realistic to expect 0.1dB at more than 50kHz if the definition of "cuts off" is so strict.
 
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