detecting true mono files

2016-05-28 13:32:51

Got a question.

I had not given this much thought and actually hadn't really payed attention to it, but this week I got a compilation album of some 60's songs and several had the addition (Stereo) behind the title. Obviously the folks putting this one together didn't go with the times as they would have better added (Mono) to the tracks not in stereo. Which leads me to the following question.

Is there a way to detect if audio files are in mono other than listening? Obviously one would check the channels metadata but sadly those all state the files are in Stereo even though they clearly are not and were just added as 2channel mono tracks which makes FB2K report them as Stereo files.

It's likely there will be more tracks in my library that are actually mono files (big oldies fan) and I'd like to tag them as such without having to listen to each of them...

Re: detecting true mono files

Reply #1 – 2016-05-28 15:02:00

The name escapes me for the moment, but there is at least one company that creates pseudo-stereo tracks from mono sources (with varying degrees of success), marking the songs as "(Stereo)" in their track lists. I suspect you have one of their releases.

Re: detecting true mono files

Reply #2 – 2016-05-28 16:42:45

no, it's not just the one release, these tracks are pure mono. Waveforms for both channels are identical in Audacity, even when zooming in to a 10 second viewport and there's no difference in magnitude between the channels for the whole track, so it's also not some kind of pseudo stereo. It's clearly audible these are just mono tracks.
There are some stereo tracks on the album but these are indicated as such, and it's not even real stereo but like backing vocals with piano or base on one channel and drums on the other channel. So either these were remastered this way or just like because stereo recording was still in its infant shoes... no idea when stereo became the norm

I checked a few compilation albums of other artists from the 50's-60's era and there too I found some are just plain mono and still set to 2 channels.

Re: detecting true mono files

Reply #3 – 2016-05-28 23:24:33

Sorry, I wasn't quite clear; by "release" I meant a whole disc rather than a single track.

I found the discs I was thinking of. They're from a company called Hasmick Promotions under the Complete 60s label and comprise three releases with every instrumental that charted in 1960, 1961 and 1962, respectively. (The intent was to do the same for the rest of the decade, but the lawyers got in the way. So they released all the instrumentals that charted in 1959.)  They do a good job using digital remastering for excellent sound from both mono and true stereo tracks. The pseudo-stereo stuff is produced by a process called DES for Digitally Extracted Stereo. As I said, it can be hit-and-miss, but some results are fairly impressive.

The '60s psychedelic era featured quite a bit of stereo experimentation/weirdness, as did prog rock going into the mid-'70s or so.

Re: detecting true mono files

Reply #4 – 2016-05-29 09:09:49

Yes, the CD Red Book standard requires stereo interleaved files, even if the source tracks are actually single channel mono. The best way to see quickly if a track is mono is to use a goniometer, a straight line instantly shows that the track contains no difference information.

https://en.wikipedia.org/wiki/Goniometer_(audio)

 Or a correlation/phase meter, if the line stays at the right (+1) you can tell it's mono.

https://documentation.apple.com/en/soundtrackpro/effectsreference/index.html#chapter=7%26section=1%26tasks=true

Re: detecting true mono files

Reply #5 – 2016-05-29 13:08:25

Ah This is all new to me. Never knew that existed. But that still requires listening or at least playing the tracks.
Yet that goniometer thing looks nice as a way to be 100% sure, and seeing as they exists as VST plugins (which I read can be used in FB2K although that it is beyond my level of audio-geekness) I think I'll make my first steps into VST land.

If nothing else it makes for a nice visual component too

EDIT: Yikes, that was quite the discovery tour.... not very intuitive how to get started. But at least I now have a gonio display very neat.
Much obliged. :thumbup:

Re: detecting true mono files

Reply #6 – 2016-05-29 16:19:04

pfew... that Goniometer display is quite revealing. Some of the tracks show a very distinct pattern while others show only slight vibrations along the vertical axis. The latter I assume are 'enhanced' mono tracks as there's very little separation to speak of.
True mono however stands out like a sore thumb.

Re: detecting true mono files

Reply #7 – 2016-05-30 07:06:50

Glad it was a helpful!

Yes, goniometers are great for a wide number of reasons. Also very easy to see how limited stuff is (if the lines keep "smashing into the edges", then you can be pretty sure the same thing is happening to the audio!)

Setting up VST suipport in FB2K is pretty easy, but I find most of them crash if I try to use the keyboard for text input, I should submit a bug report, as that doesn't happen in my regular host.