Pro Audio Asylum

• Re: No thats not an issue with Synchronous Rate Conversion - Todd Krieger 01:27:01 05/16/06 (2)
  In Reply to: No thats not an issue with Synchronous Rate Conversion posted by jcox on May 15, 2006 at 20:35:15:

  The "320/147" ratio was brought up by the late Julian Dunn of Prism Sound, which would indeed make this a "synchronous" conversion. The problem is I've yet to see the a 16/44 to 24/96 conversion actually implemented this way.....

  I don't know where the term "zero stuffing" came from.... The upsampled signal is not "zero stuffed", but calculated using a mathematical process called "convolution," where a set of coefficients representing the "Fourier transform" (within a truncated time period or "window") of the brickwall filter function is first multiplied with the a set of corresponding values from the raw signal at a specific time, and then added together, to provide the "interpolated" sample value.
  
  

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  • You are aware of "fast convolution" aren't you? - real_jj 12:54:26 05/25/06 (0)
    In Reply to: posted by on December , at :

    Consider.

    If I do f&y (& meaning convolution), f a filter, y the signal in the time domain...

    If I then calculate F (fourier transform of the filter) and Y (fourier transform of the signal), then F*Y is the exact dual of f&y.
    (* being point by point multiply, complex)

    If I then do IFFT(F*Y), I get exactly f&y. You need some guard band to prevent wraparound, but that's easy to calculate.

    Perhaps you're mistaking this for something else?
    
    

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  • I haven't been inside any DAW code so I can't say what's used - jcox 10:23:41 05/16/06 (0)
    In Reply to: posted by on December , at :

    but software to do synchronous conversion certainly exists

    http://www.soundslogical.com/support/resample/documentation/english/documentparts/resamplehelp-30.html

    cruise the site, matlab files, textbook references

    http://www.analog.com/UploadedFiles/Application_Notes/154260303EE183Rev5.pdf

    just from the first few hits from

    google: 320 147 sample rate conversion software

    The polyphase filter implementations can be thought of as the “fancy indexing” I referred to previously

    I have designed/implemented fir filters using polyphase concepts to deskew/time align data from a multiplexed multichannel adc system, so I am familiar with those big word too
    
    
    

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