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Re: Audio recording bitdepth
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Re: Audio recording bitdepth


  • Subject: Re: Audio recording bitdepth
  • From: Bjorn Roche <email@hidden>
  • Date: Wed, 2 Dec 2009 22:51:56 -0500


On Dec 2, 2009, at 9:33 PM, Brian Willoughby wrote:


On Dec 2, 2009, at 18:24, Bjorn Roche wrote:
On Dec 2, 2009, at 8:33 PM, Brian Willoughby wrote:
Note that (2^n)-1 is not bit-transparent, except for limited cases where rounding just happens to restore the original value.

Actually, I meant (2^n)-1. I tested (2^n)-1 for n = 16 and 24 with single precision floating point numbers pretty extensively and carefully and they are transparent as well. There is presumably some reason for this beyond coincidence (not enough of a change to snap it to the next quanta?), but I don't think I want to think about it anymore.


Well, your tests are not complete. For n==16, (2^n)-1 creates 14 additional bits of quantization noise. Your tests do not reveal this because the rounding step covers up the noise. Since 24-bit is only 8 bits more than 16-bit, there are still enough extraneous bits to cause the rounding to make it appear transparent, even though it isn't.

Any processing of the float values would show the added quantization noise when using (2^n)-1, but by using 2^n you're safe from additional quantization noise.

You are right that I am not measuring quantization noise converting from int to float. Usually when audio engineers speak of bit transparency in this context, they are not referring to quantization noise; rather they are referring to the ability to recover the original int value after a conversion to float and back to the original int value. In this case, you can recover the original int, so the transformation is bit transparent.


	bjorn

-----------------------------
Bjorn Roche
XO Wave
Digital Audio Production and Post-Production Software
http://www.xowave.com
http://blog.bjornroche.com
http://myspace.com/xowave


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References: 
 >Re: Audio recording bitdepth (From: Doug Wyatt <email@hidden>)
 >Re: Audio recording bitdepth (From: Bjorn Roche <email@hidden>)
 >Re: Audio recording bitdepth (From: Brian Willoughby <email@hidden>)
 >Re: Audio recording bitdepth (From: Bjorn Roche <email@hidden>)
 >Re: Audio recording bitdepth (From: Brian Willoughby <email@hidden>)

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