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View Full Version : Maintain same level after stereo to mono conversion



fylthy
10-10-2013, 05:48 AM
Hi, first I want to say - great product!

I've read a few forum posts asking similar questions about stereo to mono conversion, and the advice is always to convert to 32 bit floating, use channel mapper to convert the 2 channels to mono, volume normalize (peak to peak) and then truncate (with or without dither) to 16 bit. But I want to skip the normalize part, and have the peak level the same as the original stereo file. While I think I understand this a little, please correct me if I've got it wrong...

The loudest possible part of the new mono file will be where the two channels of the stereo file have their waves both at 0dBFS, at the same time, any other points within the file where the waves are summed will be lower than that, that is the highest it could possibly be. Furthermore, the resultant mono version then will have it's highest theoretical peak at +6dBFS (floating point). Now, I say this because I think I understand that amplitude doubles with every 6dBs, is that right? That means the high peaks have combined, doubled, therefore the new peak is +6dBFS. Also, from what I understand a 32 bit floating file can accommodate that kind of digital "over", is that also correct?

So, to get the result I seek, I need to convert to 32 bit, sum to mono, reduce by 6dBs, then truncate at 16 bit (with or without dither). Would that get me a file with the same peak level as the original, but now mono? If that is correct, how do I reduce the volume by 6dBs? Fixed amplification won't do it, because setting that at -6dBs will make all files peak at -6dBs, and that's not what I want either. I want each file to peak the same as its original mono file.

To put this in context, the actual task I am attempting is to batch convert 10,000 stereo drum hit samples (kicks, snares etc) that I need in mono, but their current peak volumes (relative to each other) needs to be maintained, I don't want them all normalized. Some are already peaking at 0dBFS, but some are no where near that, and that's fine... what's important is that I maintain that relativity.

Thanks for your help!

ps. I also considered summing each channel at 50% of it's original, which means again that the highest peaks, when combined, will be brought back up to 0dBFS. Is this a more elegant solution? Which one will get the best result?

Spoon
10-10-2013, 06:02 AM
I am not sure there is an elegant solution for this, because if you sum the channels, then depending on the audio, it could sound much quieter.

fylthy
10-10-2013, 06:16 AM
Hey man, thanks for the quick response! I guess you're referring to phase cancellation? In those case where the left and right channels are out of phase then they could cancel each other out completely (worse case scenario) or more likely just be quieter at those points in the cycles, and overall create a phasing effect. Yeah, not ideal. If I wanted to ignore that for the time being, how would you use the batch converter to take a stereo file and convert it to mono to get the result I'm looking for?

fylthy
10-10-2013, 04:10 PM
OK, so what DSP setting allows me to reduce all files by a value of x dBs? It's probably there but I'm having difficulty finding it, so apologies if I'm a bit slow on this.

Spoon
10-10-2013, 04:37 PM
Volume Normalize has a fixed normalize option.

fylthy
10-10-2013, 05:14 PM
That's not the same thing at all, and I'm sure you know it. Fixed normalize sets all files to the same level. What DSP reduces all files by a fixed amount?

fylthy
10-10-2013, 08:18 PM
So... a work around on this is to use a VST, I suppose, and I found a very simple freebie -

http://www.bluecataudio.com//Vault/Products/Product_GainSuite/Screenshots/Processed/single.png

But... will this be supported as a mono VST process? I saw another thread here where you stated that your VST implementation only supported stereo processors (in 2009) is that still the case?

Spoon
10-11-2013, 05:28 AM
On the volume normalize dsp effect is 'fixed amplification' this applies a fixed gain, + or -