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Noise Shaping

Discussion in 'audio' started by Jim Audiomisc, Feb 9, 2017.

  1. Richard Kimber

    Richard Kimber pfm Member

    It's the USB driver and DAC firmware.

    Sox can; but that's command line. I haven't come across a player with a good GUI that enables you to manipulate the various parameters. Squeezelite allows some parameter setting using the sox library. Maybe other players do, but I haven't explored them.

    - Richard.
     
  2. Jim Audiomisc

    Jim Audiomisc pfm Member


    OK. So the limit you referred to is down to the specific USB DACs requirement for a 'driver'? (i.e. it isn't compliant with the standard USB Audio Classes) Or?...

    I can recall that SoX lets you specify coefficients for a TDA FIR resampling filter. But not if it lets you specify alternative conversion architechtures or Noise Shaping filters. But then I've never looked into that. It does have a 'play' command, but again I've never checked if that lets you use all the other facilities it has! But presumably its libraries, etc, could let a good programmer base something on them.
     
  3. Jim Audiomisc

    Jim Audiomisc pfm Member

    Well, my comment was based on not having ever noticed a difference between lower rates than that! :)

    I suspect what might be 'best' in any *player* conversion would depend on the specifics of the DAC hardware. In effect, trying to tweak around any imperfections or limits it has.

    As I think I've said before, I'm not personally very keen on 'one bit' anyway. And as has been pointed out, if you have the power and flexibility of a computer program/system then, yes, it probably makes sense to capitalise on the high bit-depths available for all intermediate processing.
     
  4. Jim Audiomisc

    Jim Audiomisc pfm Member

    As per earlier comments I've now written a 'first rough version' of a simple program that will generate a 16bit LPCM wave file from a named 24bit LPCM wave file. This first version has some limitations, and is for RISC OS. However the results agree with the earlier demo when I feed it 24bit input files with test waveforms, etc. e.g. Have a look at

    http://jcgl.orpheusweb.co.uk/temp/shaped.png

    if interested. Note that the right-hand scale is nominally wrt bits per sample for a white noise background limit. And that in reality I suspect the bulk of 24bit real-world recorded files actually have noise levels around 20bits or higher, anyway!

    I'll make a tidied up version of the program (with source code) avalable on the web when I get a chance - fingers crossed, tomorrow sometime. That will let 'C' programmers see the code in its basic form. I'll then do a Linux (ROX) version and maybe add some tweaks, etc.
     
  5. Jim Audiomisc

    Jim Audiomisc pfm Member

    I've now put up an initial demo version of a program that will generate 16bit Noise Shaped files from 24bit ones. It is quite limited and is currently only a RISC OS demo example. But it does include the source code in a version of 'C' along with a 'Help file'. Anyone interested can find it here

    http://jcgl.orpheusweb.co.uk/temp/WAVNoiseShaping.zip

    All being well, I'll do a Linux/GCC version sometime. But anyone who wants to is welcome to do something better. :)
     
  6. darrenyeats

    darrenyeats pfm Member

    FWIW, after some time, for now, I've settled on 19-22kHz.
     
  7. darrenyeats

    darrenyeats pfm Member

    According to http://stackoverflow.com/questions/3578615/mp3-bitrate-detection-through-frequency-spectrum-analysis the frequency cut offs for MP3 depend on presets, so you can check using Audacity the behaviour of your MP3 converter at various bitrates (if it's not configurable). I always recommend VBR with MP3.

    The sub-20kHz roll off of MP3 might explain why some people claim MP3 sounds "nicer" than CD.

    When I checked using my MP3 converter (soundconverter using lame) 256VBR seemed to be flat to around 19kHz with a not cliff-like roll off above that. I'll probably switch from 192VBR and 256VBR for mobile duty.
     
  8. tuga

    tuga pfm Member

    Hi Jim,

    I don't know if this is of any interest but HQPlayer allows user selection of different noise shaping patterns.
    Might be worth a listen.

    Best,
    Ricardo
     

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