what are the possible options for summing Left and right signal into mono signal ?
Thread Summary
The user asked about methods to mix stereo L & R signals into a mono output for a subwoofer channel without gain discrepancies. The final answer recommended summing the signals with a 'signal add' block, followed by a 'gain' block set to 0.5 (-6.02dB) to prevent clipping. The Signal Mixer block in SigmaStudio is noted for being cycle-efficient and automatically adjusting gain.AI Generated Content
hi all,
I would like to know what are the different possible ways to mix L & R signal of a stereo audio input flow into a mono signal output.
The immediate use case is to derive a mono subwoofer channel from a fullband stereo input, and to have no gain discrepancy between the outputs (=hear mono bass and stereo non bass at the same level for the ears)
I've seen examples using and addition cell followed by gain cell, but it seem that there are many other ways do it;
So what are they and what are their respective pros and cons ?
thanks in adavnce
Cheers.
Edit Notes
note: typo fixes
[edited by: iravelo at 9:13 PM (GMT -5) on 20 Nov 2022]
summation
mono
sigma studio 4.7
subwoofer
sigmastudio
ADAU 1467
eval adau 1467z
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You can simply sum the two signals together with a "signal add" block. This is mathematically exact.
The only problem is that now any material that is common to both channels in the summed signal, as is the case for something that is already mono, will be twice as high (+6.02 dB higher) in magnitude. If you send that signal directly to an output, peaks that were just below 0dBFS will be clipped. Internally there is headroom, so if you first run your summed signal through a "gain" block set to a gain of 0.5 (-6.02dB), and THEN send the signal to output, there will be no risk of it being clipped.
Bass is almost always centered in the middle; i.e., it already is mono. Summing the Left and Right signals will create the gain problem I talked about, so in your project you will need to lower the gain somewhere in the path creating your subwoofer signal, either before or after any band-limiting EQ.
SigmaStudio includes a "signal merger" block that does the gain change for you automatically, dropping the gain in proportion to the number of input signals that it sums.
David is correct, I'll just add that I've found that the Signal Mixer is most cycle-efficient and versatile. Multiply-and-add is often a combination that is implemented very efficiently in DSP cores. So it is probably a little better than a separate add and multiply.
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