Motu M4 Measurements Collection (Noob alert!)

Discussion in 'Audio Science' started by Vtory, Feb 9, 2021.

  1. Degru

    Degru Facebook Friend

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    The 24 bit option does the same thing; both 24 and 32 bit in the wasapi plugin are non-FP so you should just select the highest bit depth supported by your DAC.

    You can manually attenuate >0dbfs files using Foobar's volume control, or using replaygain to calculate the peak of the file and attenuate appropriately.

    Foobar won't do any pre-processing of the file before playback unless you tell it to, so the output plugin is merely doing its job.
     
  2. Vtory

    Vtory Audiophile™

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    No as long as I am concerned, we don't have anything greater than 0dbfs in 24bit integer wave file by construction (145db DR). Software should call the theoretical maximum 0 dbfs. It's only 32bit float files that allows tricky range (+770dbfs to -758dbfs) as per IEEE-754.

    But it seems the plug-in did nothing in handling 24 bit output when handling 32bit float files. Foobar also supposedly don't touch anything when opening 32bit. How crazy.
     
    Last edited: Feb 12, 2021
  3. Degru

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    The wasapi plugin outputs fixed for both 24 and 32 bit setting, but the rest of foobar uses floating point.

    There simply isn't any attenuation happening by default since foobar doesn't read through the entire file before playback unless you scan with replaygain. So >0dbfs will get clipped off by the plugin before it's sent to the dac. Hope I'm making sense here.
     
    Last edited: Feb 12, 2021
  4. Vtory

    Vtory Audiophile™

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    Ok, I will take extra care of 32bit float files from now on (I am not using replay gain heavily these days except investigating headroom for some files). I don't think I've ever used such files before though. It's my bad assumptions that foobar behaves like other professional daws.

    Anyway that's one good use case where k-mixer benefits users lol.
     
  5. Degru

    Degru Facebook Friend

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    On a related note, MP3 actually gets decoded to 32FP by Foobar as well. Since MP3 (and probably some other lossy codecs) does not store absolute values internally, this can result in decoded MP3s peaking above 0dbfs. Ive seen this on a few files in my collection going a few fractions of a db over, although I've never actually heard significant clipping outside of an MP3 that was specifically crafted to abuse this issue.

    Anyway, that's probably quite enough off topic for this thread from me lol.
     
  6. Vtory

    Vtory Audiophile™

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    Just some short notes for foobar2000 users regarding M4's playback.

    M4 does not have fixed line outs for 1-2 (only trs/rca monitor outs exist).
    And its headphone outs are regarded as outs 1-2.

    So, there are several different configurations for playback. Below are my findings so far.
    • Native ASIO driver only enabled outs 1-2 in foobar (couldn't specify 3-4 unlike I did so in REW/Arta)
    • ASIO4ALL can do 3-4 outs (not to mention 1-2 outs), including pull (event) mode
    • WASAPI plugin works with push mode (24 or 32 bit output setting required), but not with event mode at any output bit depth (regardless of adjusted buffer sizes). Anyway users can use either 1-2 or 3-4, but not at the same time (ASIO4ALL can do)
    While I didn't hear annoying sound degradation of monitor outs, native asio is perhaps not ideal for external amps.
    WASAPI pull generally worked well, but a little weird short pause heard every time I play the first track after initiation (only some ms though).
    ASIO4ALL seems the best way. It can also simultaneously use 1-2 and 3-4.

    No idea why ASIO4ALL pull mode works while WASAPI event fails...
     
    Last edited: Feb 13, 2021
  7. Vtory

    Vtory Audiophile™

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    Updating this thread with something I found with one DUT (i.e., not M4 loopback). To make SW stuffs simple, I used two computers with each one running REW's RTA and signal generator respectively. Both connected to DUT and Motu M4 via Win 10 and ASIO usb (Native Asio for M4 and Asio4All+Pull mode for DUT).

    [​IMG]

    [​IMG]

    You may clearly identify which one is bus powered without additional explanation. Bal results weren't any different. I think Marv posted something similar in his early reviews, but not this much different if I recall correctly.

    In this experiment, Dell Ultrasharp 24's usb2 port and xps13's usb3 port used for M4 and DUT connections. I also tried the other way and got nearly the same results. Neither is far from "good" electricity source in my understanding though.

    Indeed I'm using Ultrasharp's usb port for M4 primarily, but Motu seems to apply extensive filtration for its usb input signal and power, which can victimize some audiophile virtues in return for lower and cleaner power noise floor. Note that there are a bunch of audiophiles who opting out power conditioning. Considering Motu and Schiit's respective customer demographic variance, how to handle bus power differently between two products could be understandable.

    Also, readers should be aware that M4's ADC isn't perfect. Any harmonics caused by 1khz main signal could be a mixture between ADC's and DUT's (likely dominated by whichever larger). If any such harmonics not drastically different from those of M4's loopback measurement, I'd rather ignore.

    [​IMG]
    [​IMG]
     

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