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Topic: A newbie asking stupid questions: Mono-detection (Read 3245 times) previous topic - next topic
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A newbie asking stupid questions: Mono-detection

I want a program that detects mono-recordings by scanning AudioCD:s and 2-channel-Wavs. Do you know anything like that?

A newbie asking stupid questions: Mono-detection

Reply #1 –
Answer to your question:
Mono = both channels are identical.
If you substract both channels (= invert one channel and add to the other), the results will be silence for mono (or something near to silence). One way to use existing software to find out if a file contains mainly silence or not is applying replaygain and check the value(s).

To do this in practise you could use
SOX (commandline wave editor) or
foobar2000 with simple surround DSP (inverts one channel) -> convert stereo to mono DSP -> diskwriter (downsampling, lower output bit depth like 8bits will help to save space - or use oggpreview plugin for applying the "test" to e.g. 10 seconds from the middle of each file.) Then apply replaygain to the resulting files and use a fb2k title formating string that displays replaygain values.

Now I have two questions

- Why do you need this?

- What's the reason for "Last time I came here I was flamed" in the thread title?
Let's suppose that rain washes out a picnic. Who is feeling negative? The rain? Or YOU? What's causing the negative feeling? The rain or your reaction? - Anthony De Mello

A newbie asking stupid questions: Mono-detection

Reply #2 –
Quote
Answer to your question:
Mono = both channels are identical.
If you substract both channels (= invert one channel and add to the other), the results will be silence for mono (or something near to silence). One way to use existing software to find out if a file contains mainly silence or not is applying replaygain and check the value(s).

To do this in practise you could use
SOX (commandline wave editor) or
foobar2000 with simple surround DSP (inverts one channel) -> convert stereo to mono DSP -> diskwriter (downsampling, lower output bit depth like 8bits will help to save space - or use oggpreview plugin for applying the "test" to e.g. 10 seconds from the middle of each file.) Then apply replaygain to the resulting files and use a fb2k title formating string that displays replaygain values.

Now I have two questions

- Why do you need this?

- What's the reason for "Last time I came here I was flamed" in the thread title?

Thanks, but this seems quite a bit.... complicated....
Anyway. I'd like to rip all my CD-tracks that are recorded in mono (mostly 20's-50's blues) to mono mp3's with half of the bitrate I'd use normally with Joint Stereo.

And I was "flamed" (in other words told to read the f-cking manual) when I asked about Lame's -alt -presets some time ago, without first reading some 100-pages of manuals and FAQ.

A newbie asking stupid questions: Mono-detection

Reply #3 –
if you can be bothered, it's always fun to re-wire the ouput from your CD player / computer so the 2 channels have opposite polarity.  then run these into an amplifier (preferably one of those old ones with a "mono" button).

play back the CD in question, hit the mono button, and if you hear anything you've got a stereo recording.

(basically the same as tigre's suggestion, but more fun as it involves pushing buttons and re-wiring.)

A newbie asking stupid questions: Mono-detection

Reply #4 –
The difficulty with your question, apecat, is that many monophonic recordings, when mastered to CD, are not mastered via a single-channel transfer. Instead, they are transferred as two-channel audio, in the same manner a stereo source would be transferred, and slight fluctuations between the channels often occur; the left and right will be nearly identical, but a phase-inverted subtraction will leave a very low-level remnant of the sound (this is especially prevalent when the best surviving "source" is a monophonic LP).

  So it sounds like what apecat is really asking for is a tool that can simultaneously analyze both channels of a stereo recording and determine whether there is an audibly significant difference... or whether, when transcoding to some other format, downmixing to a single channel will yield satisfactory results, without losing any essential elements due to phase cancellation.

    - M.

A newbie asking stupid questions: Mono-detection

Reply #5 –
Quote
with half of the bitrate I'd use normally with Joint Stereo
half of the bitrate wont give you the same quality for mono files btw.
PANIC: CPU 1: Cache Error (unrecoverable - dcache data) Eframe = 0x90000000208cf3b8
NOTICE - cpu 0 didn't dump TLB, may be hung

A newbie asking stupid questions: Mono-detection

Reply #6 –
Quote
Anyway. I'd like to rip all my CD-tracks that are recorded in mono (mostly 20's-50's blues) to mono mp3's with half of the bitrate I'd use normally with Joint Stereo.

That (half of the bitrate) doesn't work properly. (Lame) joint stereo works pretty well, on mono material it'll switch to m/s with > 90% of bits used for m and < 10% for s, so the results won't be much better if you encode with -m m or -a (downmix to mono) switch. If you use VBR (e.g. --alt-preset standard, for lower bitrate lame 3.96 -V x looks promising so far) you'll get very low bitrates (but constant quality) on (near) mono recordings automatically. IIRC you got similar advice at Winamp forums already.

Quote
And I was "flamed" (in other words told to read the f-cking manual) when I asked about Lame's -alt -presets some time ago, without first reading some 100-pages of manuals and FAQ.
I didn't have any problems to find your last thread and therefore know what you've meant. I wanted to know in what way this remark in the topic description is relevant for this topic.
Let's suppose that rain washes out a picnic. Who is feeling negative? The rain? Or YOU? What's causing the negative feeling? The rain or your reaction? - Anthony De Mello

A newbie asking stupid questions: Mono-detection

Reply #7 –
Just for info, with WavAnalysator you can detect if your audio source is stereo or mono

A newbie asking stupid questions: Mono-detection

Reply #8 –
Quote
Just for info, with WavAnalysator you can detect if your audio source is stereo or mono [/IMG]

Looks like this does exactly what I described above; thank you for the link! (Note: in order to download it, one must apparently go to the German homepage, or use a direct download link.)

    - M.

A newbie asking stupid questions: Mono-detection

Reply #9 –
If you know the CD is mono (or so close to mono that you don't care), you could just rip the left channel only (some rippers allows this) and -m m in lame.

As tigre has already suggested, you'll probably get a small file for two-channel-mono rips anyway. It has been suggested that you could reduce the minimum bitrate set in --alt-preset standard in this case (especially if you use -m m), but not too far! So maybe use -b 96. Experiment! Look up "mono" in thread titles - it's been discussed extensively before.

Cheers,
David.