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Dither after adding four PCM 16 bit signals?
post Oct 16 2012, 21:59
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Hello all!

My DSP application is implemented on a FPGA using VHDL. Basically there are four 16-Bit PCM audio signals with 48k sample rate.
After processing each audio signal separately (one multiplication with a factor that depends on a sensor) i add those four audio signals to get a unified signal.
So the question is now, when i add those four audio signals i get a 18 bit result, but i must reduce the bit depth back to 16 bit to hand it to the audio codec chip (DAC).
Should i dither in this case? Or what is the typical approach when adding PCM audio signals and then want to go back to the original bit depth?
All calculation is done in fixed point.


This post has been edited by Zopfi: Oct 16 2012, 22:00
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post Oct 16 2012, 22:27
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I'm not a DSP expert, but my intuition says that after summing 4 uncorrelated signals the "16th bit" (bit zero) is already sufficiently randomized, so you don't need dithering.

I assume you can't hear dithering at 16-bits anyway, or you wouldn't be asking... I can't hear anything 80-90dB down...

when i add those four audio signals i get a 18 bit result
Shouldn't that require 20 bits?
Edit - Nevermind.. 18 bits is enough. ohmy.gif

This post has been edited by DVDdoug: Oct 16 2012, 22:41
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