Best Way To Detect Whether Audio In A File Is Dual-Mono Stereo?

[onesikgypo]

Hi,

What would be the best way to determine whether a file has dual-mono as stereo - just as i dont wish to sit there comparing left and right channels (especially since real stereo can actually be quite similar when looking at "pictures" of the channels in audacity and alike).

Thankyou.

[Megahurts]

Subtract one channel from the other.

If the result is no sound then it's mono.

[onesikgypo]

I'm not trying to distinguish between stereo and mono, im trying to distringuish between stereo and dual-mono ("fake" stereo).

In a "real" stereo clip, the left and right channels will both contain data, but they will be different.

In a "fake" Stereo - where its Dual-Mono - Both channels still have audio, except theyre identical.

[Megahurts]

By subtracting one channel from the other, you will hear the difference of a real stereo file.

Also, you can see the difference with a X-Y graph as in Gold Wave. If the line stays straight, then it's mono.

[onesikgypo]

The X-Y Graph appears to be what im looking for - i have gold wave, but am new to it, where can i
see the graph?

Edit:

never mind, found it on the right this is what i was lookin for, thanks.

[Megahurts]

It's in the 'W Control' window. Right click on whatever is displaying the audio level and select X-Y graph.

I'm using an old copy of Gold Wave so it might not be the same.

[jman98]

I've never heard anyone use the term "dual mono" before and I suggest that in the future you don't say that again. "Fake stereo" is a more accurate term.

I'm also not sure that I would say that fake stereo has "identical" channels as you did. If they were really and truly identical, the sound would be mono. The slight differences, in the old days achieved with band pass flitering and perhaps some delay, made it sound sort of like stereo. They are identical in terms of each channel originally being exactly the same, yes, but whatever was used to fake them into stereo will make slight differences between them and if they are different, they are not "identical" any more. I'm curious to see if subtracting the channels in fake stereo really will produce a straight line or not in Gold Wave.

[manono]

Dual mono is perfectly acceptable. It's the same thing coming out of both the left and right channels. It's not 'fake' stereo. A mono source remixed to simulate stereo is sometimes referred to as fake stereo.

I'm also not sure that I would say that fake stereo has "identical" channels as you did. If they were really and truly identical, the sound would be mono.

Come on now. Mono is one channel - the center channel. Dual mono is the same thing in the left and right channels. I can point to DVDs with DD 1.0 single channel mono, some with DD 2.0 dual channel mono, and some with DD 2.0 remixed stereo from what was originally a mono source. They do a pretty good job of it too, these days, making it sound like stereo.

[Cornucopia]

The term "Dual Mono" is used in 2 different ways, both of them common...

1. General dual mono as 2channels, which normally would carry stereo/binaural, are carrying identical information on both channels. This is different from true Mono, which is 1 channel only. There is actual differences in how they are heard also. If you listen to dual mono, with equal channel volume and you sit equidistant to both speakers, room walls, etc., you should actually perceive a PHANTOM center channel only, not 2 separate sources. A true mono setup would have the speaker be IN the center, providing a REAL center signal instead of a phantom signal (and there are EQ differences between the 2 types).

2. Specifically, "Dual Mono" is one of the standard options when doing lossy 2ch audio encoding in, e.g. MP3 or AC3 or AAC. The significance of this is that there is no implicit Inter-relatedness in this setting, either in content or in bitrate allocation. This is unlike some of the other settings (1ch, joint stereo--using ~blended content and flexibly-related bitrates, and stereo--using UNBLENDED content but flexibly-related bitrates). D.M. expects both channels to be fully independent of each other (whether they are or not), and doesn't "borrow" surplus bits from 1 channel to the other.

....back on topic again...

IF the signal isn't 100% completely identical, subtracting 1 channel from the other won't fully work. Assuming their relative phase is identical, you can fix this somewhat by separately normalizing BOTH channels, then doing a subtraction (done by reversing the polarity/phase of 1 channel and then equally mixing/adding the 2 channels together). As an additional enabler, and to make any DIFFERENCE more obvious, you should NORMALIZE the result. You'll then easily notice how it'll be either COMPLETELY SILENT (even after normalization)--GOOD, or mostly silent with little BuRsTs of LOUD ?Garbage?--signal is supposed to be identical but isn't completely, or it sounds like a "hollow", reverb-like regular signal--in which case you've got a regular stereo/binaural/Dobly signal in those source channels. (edit: or it'll be a regular loud mono signal, in which case it WAS dual mono, but the signals were ORIGINALLY out of phase with each other)

This should be scriptable, too, if you need to batch it.
Or you could use the "X/Y" graph (more correctly called a "Lissajous" scope/monitor. See http://en.wikipedia.org/wiki/Lissajous_curve. It is more helpful than a simple X/Y because it show Phase differences also)

If you'd like a freeware scope app, here's one: http://www.zeitnitz.de/Christian/index.php?sel=scope_en

Scott

>>>>>>>>>
edit: you can also do a google search on "correlation meter" for similar tools...

[jagabo]

Best Way To Detect Whether Audio In A File Is Dual-Mono Stereo?

Listen to it. Especially with headphones.

If you listen to dual mono, with equal channel volume and you sit equidistant to both speakers, room walls, etc., you should actually perceive a PHANTOM center channel only

[lacywest]

I use Cool Edit Pro 1.2a ... or Cool Edit Pro 2.1 .... and zoom in on the wave form ... if both channels are mono ... the wave form will be exactly alike when u see both of them ... very easy to see.

If they are stereo ... for reals ... there will be differences between the left and right tracks.

[jman98]

manono & Cornucopia - I stand corrected about the term "dual mono". Again, I have never heard this term before. Never. But apparently you have so it must be in somewhat common usage.

However, I think we have a question of semantics. The original poster is not talking about what you are talking about. Yes, I have heard of AC3 2.0 which even in mono I've never heard of being called "dual mono". What I meant is that you have identical sounds in the 2 channels. you will get a single (phantom) mono channel in the center when you listen. The original poster is talking about potentially modified channels which are not, I still think, technically "dual mono" since they have (potentially) been modified. But I'm not going to argue this endlessly.

I agree with Cornucopia and jagabo that simply listening is a great test.

[jagabo]

The original poster is talking about potentially modified channels which are not, I still think, technically "dual mono" since they have (potentially) been modified.

No, he described it as both left and right being identical:

In a "fake" Stereo - where its Dual-Mono - Both channels still have audio, except theyre identical.

[dLee]

When I hear the term "dual mono", it most frequently refers to a mono signal (from mic or mixer) recorded onto two tracks of a videotape by the camera during image capture / recording.

[lacywest]

Something else about dual mono ... coming out of both front channels. If your sound system is of the newer kind ... that has ... left front and right front and rear left and rear right ... and a center channel and a subwoofer channel. You wont get any sound from the back channels ... if the front left and right are not stereo. Unless you have chosen a setting on your receiver that simulates stereo from a mono signal ... and it usually sounds yucky.

[lordsmurf]

Look at the waveform -- it will match.