Okay I have a question I have The Beatles Anthology CD's and some tracks are in stereo and some tracks are in mono. I have Adobe Audition and is there any option to let me know if a WAV from a CD is in mono or stereo? I ask this because I'm converting the anthology tracks to mp3 and I want the tracks that are in mono on the CD to be mono MP3's. I know I can look at the waveforms but sometimes it too similar to tell if the same info is being pumped out both channels as mono songs on CD's are. So can anyone help with this?

There's really no need to worry about that with regards to encoding to mp3 as joint-stereo will take care of this with a minimal increase in size.

Well the problem is I already encoded the albums in mp3 and found track listings online from different sources telling which ones are in mono. Should I redo the albums as joint stereo just in case I encoded a stereo file into mono? BTW I went from CD TO FLAC, all FLAC files are in stereo, even for the mono tracks on the albums they all say they are in stereo under dbpoweramp. I'm guessing that means its the same info on both channels right? and when I decode to WAV it will be same to the original?

If I accidentally forced mono encoding of stereo files, then yes, I'd redo them.

Back to your original question, you can tell if a ripped track is mono by subtracting one channel from the other. This can be done by simply using the vocal cut preset in the channel mixer.

EDIT: Answering your other questions in your edit...
Mono tracks on a CD still have data for two channels even if the data is identical, though this isn't always necessarily the case for mono tracks. The data can be slightly different between each channel. Converting your flacs back to wave will of course give you back the original data as it was ripped. Lossless is lossless.

Okay I'll prolly just re-encode them into joint-stereo. But clarify this 1 more thing mono tracks on CD are still technically stereo because of the 2 channels, even though those two channels have the same info on them. Sorry for the questions but these albums with both mono and stereo where confusing to me, I'll using joint stereo from now on and mono for mono only albums like the mono box set that just came out.

to answer the question: you can do this with a vector audio scope (or phasescope) (looks like this). if you see only one line in the middle (M), then it's mono.

Personally, I'd probably use joint-stereo for mono CDs, though mono encoding is fine provided they work ok with your media player.

Ya they work fine and do you know if any free vector audio scope program?

A file can be mono because of only containing one channel, but a CD always contains two channels. The only thing that would make a CD "mono" is if both channels contain identical information.

As greynol said, there is no reason to encode your mp3 as mono if you are using VBR encoding (which I hope you are). If you encode to VBR with joint stereo then your file will be essntially the same size as a mono VBR file, and will have the same quality.

Im using CBR 320kbps for my mp3s

In that case they are twice as big as they need to be for mono material. If you switch to high quality VBR then not only will your stereo files be smaller with usually no audible difference, your mono files will be less than half the size.

Thanks to everyone clearing this up, I just wanted my Beatles rips and encodes to be perfect, I'm very over obsessive when it comes to my Beatles collection.

From my experience, that's not quite true. The bitrate of a dual-mono track encoded as joint stereo will usually be ~20% above mono bitrate. I can't find it right now, but there was a topic where Gabriel explained that issue.

However, the main reason for me to encode supposed mono records to mono MP3s is that many (about the half really) mono records on CD have been expanded with some fake stereo effects. These effects very effectively knock out the channel correlation handling in joint stereo mode. Thus you will get a better (=more original) sounding file at ~90kbps (comb-filtered fake stereo reversed by downmixing to mono) than the ~200kbps file you'll get by just encoding it as joint stereo (I really don't know why, but those comb filter files will bloat even more than by factor 2).

As was discussed here recently, the results you will get from downmixing fake stereo are highly variable. You may be better off leaving them as fake stereo.

Your problem:
As far as verifying that the left and right channels are perfectly identical, you can use Audacity to invert one of the channels. I think you could split the channels into separate tracks, then pan them both to the center. Render that to a wave file, then see if you have all zeros.

Side note related to mono recordings, if you're interested:
I have a version of Miles Davis' album, "Bags' Groove," called, "Bags' Groove (20 Bit Mastering) [ORIGINAL RECORDING REMASTERED]," released in 2001. It's a mono recording, but the channels are reversed polarity. It creates a very displeasing effect. If you're listening on speakers, the sound changes dramatically as you move your head around, due to phase cancellation of different frequencies.

When you sum the channels, you get an extremely low amplitude signal. Something got messed up along the path from the analog tape to the digital domain, and I'm very surprised that the mastering engineer didn't fix this problem. The mastering engineer probably could have reversed the polarity of one of the channels, done some alignment, then used a processor to extract the part of the signal present in both channels. This might have made the recording less noisy. But I guess that's too much work for a classic jazz recording.... Unbelievable!

Here is a simple, free VST-plugin called PhaseBug which lets you check signals for phase errors, but can also be used to test if a stereo signal is in fact dual mono. Just enable the downmix-switch and drag one of the channels down by 180° - if it's mono, both channels now should eliminate each other, resulting in silence. There may be some crackle or echoes left if the analogue source had been dual mono already.

If you want to check if a CD is mono, there's no better utility than Tau Analyzer. It's actually made to check if a CD is from a lossy source, but it generates a fine frequency graph of both channels. If the two curves are identical, it's mono. With some experience you can even tell whether the graph shows a real or a fake stereo track.


That's one example of the above mentioned fake stereo records... it's a very annoying effect indeed. The good side of that particular effect is, that unlike others, it's very easy to fix. The PhaseBug plugin suits just perfectly for that task as it lets you phase-shift the signal by 1°-steps while listening to the outcome.


Right, but there's a very reasonable way to tell about possible negative effects (other than listening): compare the original frequency graph to the graph of the downmixed file. If there are any drop-down's, the signal had been maltreated by some frequency-related phase shift, which causes phase cancellation in downmixing. If not, it's just fine.

Encode mono (both channels the same) CDs as joint stereo, just like stereo CDs.

By making the mono tracks really mono, you'll save a little space, but waste a lot of time, and potentially store up incompatibility issues later on.

(everything should play mono files just fine, but who knows? I've found two specific situations where it fails)


The way to ensure that mono is really mono is to invert mix paste one channel over the other with dithering disabled. Channel mixer (vocal cut) can be used to do this. If the result is digital silence (zoom in to verify, or use waveform analyse), then the original is really mono. Anything else reveals the difference between the two channels. This technique is far more sensitive than using a vector/phase-scope or comparing the frequency response of the two channels.

Cheers,
David.

Found it.

I remember that discussion. Nowhere does it say anything about a 20% increase in size, however.

Of course it does, but isn't it real mono just because there's some hiss left? I gues it would be more appropriate to say, if there's no information left, it's mono (though technically speaking l is not identical to r, thus you get no digital silence).


That's from my experience. About 110kbps in joint stereo reduces to about 90kbps in mono (both -V2). I could test it again on some tracks and post the exact values later.

Source: Disc 1 of The Folkways Anthology of American Folk Music (44min., dual mono).
Lame 3.98r -V2: 112kbps
Lame 3.98r -V2 -mm: 92kbps
All of the tracks are dual mono with l=r (giving digital silence if l is inverted and downmixed)

Nope! It certainly won't be "seen" as mono by the mp3 encoder - i.e. the difference channel will be non-zero in joint stereo mode.

Dither doesn't matter - but it's rare to get substantially more than dither without there being something significant enough that it requires attention. e.g. mono master tapes, played back on a stereo machine, copied to CD in stereo, are potentially going to have all kinds of issues and often shouldn't be summed to mono.

Cheers,
David.

It actually sounds pretty good by inverting the right channel.

Of course not, but semantically (not technically) it's mono content because there's no stereo information in it...


What kind of issues could that be? Phase differences can be handled with i.e. the above mentioned plugin. Speaking from my experience (I downmixed a whole bunch of fake stereo / dual mono records over the last weeks), many will actually improve by downmixing. i.e there where some tracks with some annoying impulsive hiss on it (probably caused by phase errors introduced by the stereo playback of mono tapes). That hiss completely vanished through downmixing.


That's exactly what PhaseBug does if you drag one channel down by 180°. The advantage of that plugin is, however, that you can correct signals which are out of phase by any amount of degrees - small phase errors are sometimes introduced by analogue equipment.

Yes, but that's still "doing something". The easiest choice is just to encode joint stereo. The second easiest choice is just to keep one channel.

By the time you're having to use Tape Restore Live fix azimuth and sum to mono, it's more like audio restoration than CD archiving! Which is fine, and I do it - but just keeping everything in stereo is easier for most users. Agreed that there's an opportunity to improve things - but there's an opportunity to make things far worse too .

Cheers,
David.

I've seen a lot of mono releases nowadays use different noise shapers in both channels. This will fail any bit-comparison mono test, although one could argue the sound quality of such a scheme is superior to bit-exact tracks.

A channel subtract should identify these tracks as having a very constant noise-shaped difference signal, probably no higher than -60 to -70dbFS, and not varying in spectral content. An averaged spectral comparison between the two channels ought to work too (should come out to some ridiculously low spot deviation between the two channels, like +-0.01db).

Even without using Audacity or Audition, if one is encoding a mono file using LAME.exe, it can be seen as ~100% MS in the DOS window, when on the default joint stereo mode.

The benefit can be seen when encoding using VBR, as greynol posted earlier. No need to downmix to mono when using default JS, but no improvement in bitrate on CBR 320.

I have "The Beatles - 1" and "Elvis Presley - 30 #1 Hits" CDs with several mono tracks, and encoded them to my favorite -V2 setting with no need to downmix the wav file to mono before encoding. LAME VBR is intelligent enough to determine the bitrate computation for two identical channels from the CD.

Could you do so? I don't understand why such a method would be superior to bit exact tracks...


Strange, isn't it?


Just because that's always told it isn't necessarily true: as I have shown, the jont stereo mode bitrate for two identical channels is ~20% higher than of the mono mode. IMHO that's quite a difference.

Ah, but which is "correct"?

btw, Gabriel explained that it's because mono is processed as-is, while the sum channel is L+R/sqrt(2) - so in stereo mode the whole signal looks 1.4x louder, which affects the ath processing, hence more bits are used.

I've got to say it one more time: which is "correct"?

Cheers,
David.

Thanks guys for making my life much easier! You guys are awesome thanks for the knowledge

Because encoding a high-res mono source to two noise-shaped 16-bit channels is (more or less) equivalent to a single 17-bit noise-shaped channel. Assuming you do the downmix properly, you're getting 6db for free.

Hmmm... Doesn't that introduce the danger of clipping? Applying replaygain will fix it, but does that mean that we should NOT be recommending in general to encode mono material as JS stereo?

But can you count on the playback system to sum these as a "virtual single-channel 17-bit system"?

I would be worried about listeners actually hearing left-right differences, or even worse, people using surround-systems where the difference-channel is routed to the surround speakers.

-k

I'd say it's "correct" if the targeted VBR quality level is the same as for real stereo content. Either the joint stereo bitrate on mono content is too high or the mono bitrate is too low... from Gabriels explanation I guess it's the former.


Ok, got it. Now please show me a 50s master tape with a dynamic range above 96db

@northpack: i stated no improvement over CBR 320 for mono tracks. would you suggest to the OP to encode using CBR 160-192 -mm just to decrease bitrate?

while there is the obvious increase in bitrate for VBR JS vs Mono encoding, what i mean by LAME intelligently computes bitrate is that it would bring it down compared to a dual stereo track. what is 20% increase in bitrate than to worry about which tracks to downsample to mono? Taking such additional step, i believe, is not equitable to the bloat in bitrate.

No, it doesn't mean that at all. That's the internal representation. The output is L and R, and L=(M+S)/sqrt(2) - so you get back the same level you started with. mp3s never clip internally* - there's bucket loads of headroom.

* - unless you abuse mp3gain to introduce many tens of dB above digital full scale - and even then, it's not actually clipping you get.

Cheers,
David.

I put the smiley because whichever answer you gave, I can argue against it.

e.g.

the mono threshold must be correct - because the stereo threshold implicitly takes account of binaural unmasking which can't happen with a 100% mono recording - so it's right that true mono can have 3dB more noise and still be encoded transparently.

or...

the stereo threshold must be correct - because otherwise if you take a mono track and pan it fractionally left, it's still the same music, but supposedly we need a 3dB lower noise floor to encode it transparently?! And if you take a stereo track and progressively narrow the stereo separation, there's apparently a moment between almost mono and really mono where the noise floor for transparent encoding jumps 3dB!? This makes no sense. Therefore the truth must be that the tunings for stereo are correct, and are still correct when the stereo content happens to be mono. The "stereo" tunings are just re-used in mono (single channel) mode, but without the scale factor that was used during the tuning and testing of stereo, and so are 3dB wrong.

Take your pick! I remain on the fence as to which is "correct"... but encoding mono as joint stereo (unless it's something that needs proper audio restoration) is easier - no point checking that tracks are really mono just to save some bitrate that might theoretically be needed anyway!

YMMV - I think the single channel mono encoding sounds fine too. I just don't see the point of encoding CDs that way.

Cheers,
David.

If it is mono then it should null out of you convert the file to a stereo file, reverse polarity on one the two channels and then sum them together to a mono track again. Correct me if I'm wrong. Regards

You're right, though there's no need to convert to stereo since tracks ripped from CD are always two channel. You might want to re-read this discussion since we went over this already.