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Dither after adding four PCM 16 bit signals?
Zopfi
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.

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This post has been edited by Zopfi: Oct 16 2012, 22:00
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Arnold B. Kruege...
post Oct 16 2012, 22:30
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QUOTE (Zopfi @ Oct 16 2012, 16:59) *
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.


The global rule is that whenever you reduce the resolution of a digital signal you will have a new quantization error that needs to be randomized (dithered).

When you process each audio signal separately and reduce its gain, the same rule applies unless you are able to carry forward all of the bits generated by the multiplication.
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