Reverb Impulse files: do bit and sample rates matter?

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pdarg
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2009/12/22 17:28:38 (permalink)

Reverb Impulse files: do bit and sample rates matter?

I was using Sonar’s PerfectSpace Reverb plug-in, but recently upgraded to the full version (PristineSpace) made by Voxengo.
 
I record audio in 24 bit/44.1 kHz.
 
I have a collection of WAV reverb impulse files. Some are 24 bit; others are 32 bit. Some are in 44.1 kHz and others in 48 kHz.
 
The files provided by Sonar for PerfectSpace all seem to be in 32 bit/ 44.1kHz format. Is it safe to assume that 32/44.1 kHz is the most compatible file format for reverb impulse files when recording/mixing at 24/44.1kHz (and using 32 bit float for mixing/plug-ins)?
 
Are there any concerns about reverb sonic quality when using an impulse file that is in a different sample rate than the recorded project?
 
What about different sample rates?
 
Anyone have any insight on this issue?
 
I guess what I am really asking here is: should I strive to use only 44.1kHz sample files for reverb impulse in 44.1kHz projects?
 
Thanks in advance.
#1

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    pdarg
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    Re:Reverb Impulse files: do bit and sample rates matter? 2009/12/22 20:47:09 (permalink)
    Hmm . . . all quiet? Silent night?
    #2
    bitflipper
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    Re:Reverb Impulse files: do bit and sample rates matter? 2009/12/23 00:31:23 (permalink)
    High sample rate IR files are not necessary for convolution processes such as reverb emulation. Although a very slight improvement in quality might be gained, the CPU overhead increases exponentially and negates the quality benefit by making the process potentially impractical.

    The sample rate of the IR file must match the sample rate of the input data, so a 48KHz IR in a 44.1KHz project would indeed require SRC. That, I believe, happens when you load the IR file, so it doesn't add overhead during playback. It does, of course add a very slight amount of distortion, but not enough to be concerned about.

    Now, I am guessing on this one, but I suspect the wordlength is also changed to match the audio data. Because SONAR converts all audio data to floating-point, I'm guessing the IR would be similarly converted. So a 24-bit IR would be converted to 32 bits (or 64 bits). But that's also a non-issue: lengthening wordlength does not harm fidelity nor incur overhead.

    Bottom line is: don't worry about it. Use the IR that sounds best.


    All else is in doubt, so this is the truth I cling to. 

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    #3
    DaneStewart
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    Re:Reverb Impulse files: do bit and sample rates matter? 2009/12/23 02:37:42 (permalink)
    Once again, bitflipper's response makes me feel a little better about the world.


    #4
    mike_mccue
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    Re:Reverb Impulse files: do bit and sample rates matter? 2009/12/23 08:30:09 (permalink)
    FWIW, Aleskey specifically answers this question as it pertains to Pristine Space on his forum at Voxengo. He explains a bit about sample rate conversion as well.

    It's in the convolution section of the forum.

    best,
    mike

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    #5
    Paul G
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    Re:Reverb Impulse files: do bit and sample rates matter? 2009/12/23 11:06:39 (permalink)
    I have heard that using a true stereo convolution plug, (like Pristine Space), with stereo IR's will yield better results.  I haven't tried it myself, though.

    Paul

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    #6
    pdarg
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    Re:Reverb Impulse files: do bit and sample rates matter? 2009/12/23 11:08:48 (permalink)
    Yes, I just heard directly from Aleksey as well, and he confirms that bit rate is not a factor (which is similar to how Sonar treats audio when it imports it); the sample rate is a factor but a minor one, so ideally, files of 24 or 32 bit with 44.1kHz rate would be best for me, but on the other hand 48kHz files probably don't really hurt the sound too much.

    Thanks!
    #7
    pdarg
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    Re:Reverb Impulse files: do bit and sample rates matter? 2009/12/23 11:09:51 (permalink)
    Paul G


    I have heard that using a true stereo convolution plug, (like Pristine Space), with stereo IR's will yield better results.  I haven't tried it myself, though.

    Paul


    PerfectSpace is pretty good, but Pristine Space is a little bit better - something about the stereo quality does make a difference.
    #8
    DonM
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    Re:Reverb Impulse files: do bit and sample rates matter? 2009/12/23 11:19:13 (permalink)
    bitflipper

    The sample rate of the IR file must match the sample rate of the input data, so a 48KHz IR in a 44.1KHz project would indeed require SRC. That, I believe, happens when you load the IR file, so it doesn't add overhead during playback. It does, of course add a very slight amount of distortion, but not enough to be concerned about.


    Bottom line is: don't worry about it. Use the IR that sounds best.



    Bit:
    Good post - question though shouldn't the convolution tool consider the project SR and the input clip SR and perform the SRC internally.  Heck, if I wrote a convolution tool it would do that - anyway I ask because I own a couple of Convolution tools and I'm pretty sure I've either did this wrong or the tool took care of the SRC internally - now you got me thinking and I'm going to have to check it out ....

    BTW - I am huge fan of Sony's Acoustic Mirror - and I use that 99% of the time for all of my convolution in Sound Design - more important to me than reverb - again I'll bet you I ether messed this up at one time or it did an SRC for me and I never even thought about it - thanks for making me think about it...

    -D
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