How to determine if L and R channels of a stereo track are t

[classic35mm]

Hi,

I'm running Audacity 2.1.3 on Windows 7; I used the .exe installer to install. I'm relatively new to Audacity and audio production.

I ripped an audiobook from an audio CD to an MP3 file using Windows Media Player 12. When I import the resulting MP3 file into Audacity, I see that the audio is stereo (stereo, 44100Hz, 32-bit float) -- there are L and R channels.

However, the L and R channels look identical -- their waveforms look identical. Does that suggest that I can safely convert the stereo track to mono without loss of quality? Is there a way to check that the L and R channels are indeed identical?

Thank you in advance!

[Trebor]

... Is there a way to check that the L and R channels are indeed identical? ...

Split the pair into two mono tracks via "split stereo to mono", then invert one of them, then play.

There will be total silence if they are identical : total destructive interference.

[ if you can hear faint computery noises they were probably identical before they were converted to mp3, and you're just hearing the mp3 compression-artifacts ].

[kozikowski]

I ripped an audiobook from an audio CD to an MP3

First mistake. The sound on an Audio CD is perfect quality WAV, 16-bit, Stereo. You just added MP3 compression distortion to your rip for no good reason. This is a particular problem if you need to do post production. MP3 distortion gets worse at every step.

Do everything in WAV

The sound on a CD is always stereo, but it is recommended by ACX Audiobook to submit your job to them in Mono. So you are almost certainly right. The work is Mono. You can check this by splitting the stereo show into two with the dropdown menu on the left of the track. Select one of the two tracks by clicking just above MUTE. Effect > Invert. Menu > Make Stereo Track.

Tracks (top row) > Stereo to Mono.
I expect the show to vanish, the two WAV tracks are mirror images of each other. This is one of the places where MP3 may not work right.

It's possible the music interstitials, intro and outro are Stereo, so check those, but I think it's perfectly safe to reduce to Mono.

And only then convert to MP3 for your personal music device.

Koz

[classic35mm]

Thank you, everyone! I'm so thankful for the helpful feedback!

I did what you said, and it seems that everything is mono except the intros, outros, and interstitials -- just as you said. So it's probably safe to convert to mono.

One follow-up question: what does Tracks > Stereo Track to Mono actually do? Does it just take the average of the L and R channels?

[kozikowski]

It divides both tracks in half so they don't overload and then just smashes them together—adds them up. If they're identical, you'll get one single blue wave at identical volume.

Koz

[steve]

One follow-up question: what does Tracks > Stereo Track to Mono actually do? Does it just take the average of the L and R channels?

Yes.
What it literally does, is to add the two audio channels together ("mix"), then halves the amplitude.