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FlatStereo, Do you know any software to do it ?
PatchWorKs
post Jan 22 2005, 10:59
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I found this interesting procedure:

QUOTE
If recordings are converted from stereo to mono using traditional methods (i.e. pressing the 'MONO' button on an amplifier), some sounds will get lost in the process, making the result sound less 'full' or even distorted. FlatStereo, a technology created especially for Weird Titan Radio, completely solves this problem. The sound is converted to mono in two steps:

    * Remove phase shifts between left and right channel.
      This results in a recording where each channel sounds exactly the same as it did before, but a part of the stereo effect is lost. (The phase for the left and right channel is equalized)

    * Convert the two channels to one channel using traditional stereo-to-mono methods (similar to pressing the 'MONO' button on an amplifier).
      This results in a mono signal, where all sounds from the original recording are still present.


Can someone help me to find a software (open sourced, if possible) that do this ?

Thanks in advice !
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PatchWorKs
post Jan 22 2005, 12:00
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Well... after some surfing i found Advanced Audio Corrector (by Dmitry Sknarev) that allows to remove the phase distortions in high-quality audio files.

Still testing....
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MugFunky
post Jan 22 2005, 16:17
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i'm not sure, but i think cooledit/audition can do it through effects>filters>centre channel extractor.

there's certainly phase settings there, and FFT stuff going on. i just gotta figure out what all those settings actually do.

i seem to remember VirtualDub having a similar filter too, if you want something free.
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precisionist
post Jan 24 2005, 16:58
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QUOTE (MugFunky @ Jan 22 2005, 04:17 PM)
i'm not sure, but i think cooledit/audition can do it through effects>filters>centre channel extractor.

there's certainly phase settings there, and FFT stuff going on.  i just gotta figure out what all those settings actually do.

i seem to remember VirtualDub having a similar filter too, if you want something free.
*

It can be done manually at least:
CEP has a "graphic phase shifter" and the "full mix" preset in its "channel mixer". What I don't know is how to get the phase information in order to revert and apply it...I'm gonna test it.


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Specy
post Nov 27 2008, 21:24
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Stereo Tool contains the FlatStereo filter that was described above. In fact it contains 2 different filters: One repairs Azimuth problems without touching the stereo image (even if the Azimuth offset changes during the recording) - but that's not what you need when converting stereo to mono. If you want to convert stereo to mono without loosing sounds, just move the "Width" and "Phase" sliders in the "Stereo Image / Flat Stereo" panel to 0, as described in the Stereo Tool help pages.

Note: The Winamp plugin and command line versions of Stereo Tool are free, the VST plugin unfortunately is not.
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kwanbis
post Nov 27 2008, 23:07
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You are replying to a 3.5 years old post. You better start a new post.


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2Bdecided
post Nov 28 2008, 10:57
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I implemented something like this in MATLAB in 2003. I'm guessing I wasn't the first. wink.gif

IIRC the azimuth corrector, which does a similar thing, has been available in high-end audio restoration tools for a long time.


That Hans van Zutphen chap is very smart - his tape restore tool for Winamp is great...

http://www.hansvanzutphen.com/tape_restore_live/

Cheers,
David.
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PatchWorKs
post Nov 28 2008, 11:35
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QUOTE (kwanbis @ Nov 27 2008, 23:07) *
You are replying to a 3.5 years old post.
...means that i'm still looking for a valid solution ! crying.gif

QUOTE (2Bdecided @ Nov 28 2008, 10:57) *
IIRC the azimuth corrector, which does a similar thing, has been available in high-end audio restoration tools for a long time.

Interesting, BTW i'm not looking for just azimuth corrector...
I'm interested in obtaining the best quality of "downmixed to mono" audio file: so phase correction, azimuth, bass centering, etc...

According to this page
QUOTE
Some example uses:
    Goal: Mono output.
  • Set phase and width both to 0. This results in mono sound, but without the loss of sounds and distortions that normally occur when converting from stereo to mono.


The other problem is to understand if is better to resample (@32KHz) before or after the downmixing...

Here's the related 3ad @ Stereo Tool's forum !

If someone is able to help me to build the commandline pipe encoding, I'll apreciate mutch.

Thanks in advice !!!

This post has been edited by PatchWorKs: Nov 28 2008, 11:57
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2Bdecided
post Nov 28 2008, 14:32
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Now I see your application, I'd debate the usefulness of doing this.

Firstly, almost no one else does this. So any recording engineer good at their job will monitor a mix in normal mono to check what happens. Many don't, but mono compatibility is important, and those that check for it, aren't checking for it by fixing the phase first.

Secondly, intentionally or semi-accidentally, some of the "not quite in phase" parts of the mix should cancel out in mono (IMO). Think about reverb: it has a lot of components, some of which cancel nicely in mono. This is a good thing - the mono mix needs less reverb to sound "right" - preserving all the reverb from the stereo mix will make it sound muddy. Tweaking it to stop this cancellation is a bad thing.


Now, there will be parts of the mix that get lost when converting to mono (especially if it's not been checked in mono), and if this is because of phase errors, it could sound quite nasty. However, the other reason mono sounds different is because things in the centre sound disproportionately louder than things in one speaker or the other when mixed to mono compared to the stereo original. This is a thorny issue, though maybe there's a different trick to solve this one?

Finally, you're targeting a fairly low quality encode. Stereo phase errors when summed to mono is probably the least of your issues - unless the source is from a domestic analogue cassette tape, in which case some audio restoration might be in order anyway.

It would be interesting to try some samples.

Cheers,
David.
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