Convert stereo to mono

[bythecshore]

Yesterday I recorded a 45 minute meeting and am now trying to make it small enough to email to people who weren’t there. Right now it's way too big, about 45 megs.

What I'm thinking is to first convert to mono, which should cut it in half... right? Will the listener then only hear one track or the mono track in both ears (preferable)?

Second, I'll set the mp3 export preference at 16 or 24 bits... it's now at 128.

Does this make sense... and most importantly, how do I convert the stereo to mono?

(I'm using version 1.2.5 on an iMac, OS 10.4.11)

[whomper]

...
...first convert to mono, which should cut it in half... right? Will the listener then only hear one track or the mono track in both ears (preferable)?
Second, I'll set the mp3 export preference at 16 or 24 bits... it's now at 128.
...

first back everything up
save the file as testing smallifying or something
then only diddle the extra copy

select the track
under track header
choose stereo to mono
you should be down to 22-23Meg

whether it plays in one or two or more speakers depends on the users device to play it back with

dont confuse bit depth with sample rate
if it is at 24 or 32 bit depth change it to 16
that will bring you to 11-16Megbyte range
which is still pretty big for email

then you need to convert to mp3 and use a low sample rate so as to get your acceptable file size. mp3 compresses also so you get smaller file than just the sample rate change.

try the best quality first as a guide to size.
then cut back again to make it small enough for your email.
the more you cut back the less the quality. you need to make that trade off.

personally i would post the file and let them dl it
that is much easier all around than using email as a file transport protocol imho

[steve]

What I'm thinking is to first convert to mono, which should cut it in half... right?

Not exactly. When you export in a compressed audio format such as MP3, the "compression settings" determine how many "bits" of data (digital 1's and 0's) are used for each second of audio. If you export as MP3 at 128kbps (128 thousand bits per second), then it doesn't matter if it's a mono or a stereo track, the file will still use 128kb for each second of audio.

Where the benefit of converting to mono comes in is in the trade-off between file size and sound quality. The more you compress the audio, the less "bits" are used for each second of audio. This is achieved by throwing away some of the "less important" data. So compressing to 64kbps means that 64 thousand "bits" are used for each second of audio, which will produce a file that is about half of the size of the same audio compressed at 128kbps, but because a lot more data has been discarded the sound quality will be less good. The advantage of converting to mono is that you start off with less audio data (one audio channel rather than two) which means that you can compress to 64kbps and have almost the same sound quality as a 128kbps stereo file, but in only half the file size.

As a rough guide:
160 or 198kbps - good for stereo music
128kbps is generally thought of as the minimum (smallest file size) for reasonable quality stereo music
64kbps OK for mono music
32kbps and lower for speech.

Will the listener then only hear one track or the mono track in both ears (preferable)?

When you play a mono file, you will hear it in both ears.

and most importantly, how do I convert the stereo to mono?
(I'm using version 1.2.5 on an iMac, OS 10.4.11)

As with many things, this is easier to do in Audacity 1.3.12 than 1.2.x, but as you are currently using 1.2.5

1) Click on the track name (left side of the track).
2) From the drop down menu, select "Split Stereo Track"
You now have two mono tracks, but one is set to the Left channel and the other is set to the right channel.

If your original recording was made with a single microphone, both tracks will be identical, so you can simply set one track to "mono" and discard the other channel:

3) Click on the track name for one of the tracks and from the drop down menu select "Mono".
4) Click on the [X] on the top left corner of the other track to delete it.

If your original recording was made with a stereo microphone, the two tracks will be different so you will need to change both channels to mono and mix them together. Mixing the two tracks together may cause the resulting track to be too loud and distort, so it may be necessary to reduce the volume of each track before you mix them.

3) Click on the track name for one of the tracks and from the drop down menu select "Mono".
4) Repeat for the other track
5) Select both tracks and from the Effect menu select "Amplify" and amplify by -6dB (minus 6)
6) Select both tracks and from the Project menu select "Quick Mix".

In either case it may be a good idea to use the Amplify effect to bring the peak volume up to about -0.3 dB before you export.

It is likely that your finished MP3 file will still be pretty large, but rather than e-mailing it directly you could upload it to a free file sharing service such as sendspace.com then e-mail a link to the members.

[bythecshore]

Thanks to both of you... Steve - your direction were particularly detailed and easy to follow. It worked!

[kozikowski]

<<<your direction were particularly detailed and easy to follow. It worked!>>>

Be sure and also follow the direction where he told you to upgrade to Audacity 1.3.12. There are some serious shortcomings with the older Audacity 1.2.

http://audacityteam.org/download/beta_mac

If you're on a modern Mac, Audacity 1.2 is no longer supported. It's only a matter of time until it does something messy to your show and the damage is usually permanent.

Koz

[fjchild]

I'm pleased to see these good answers but still have problems. (Yes, I will get the beta soon.)

Using v.1.2.6 on Win XP and working from YouTube.

My mp3 file, so far, is 474k for an 18 sec clip. I need to get it down to 300k to use for a ring tone.

I'm not getting anywhere. I exported as mono but, as suggested, the file is the same size. I am offered only three options, 32-bit float, 24-bit, 16-bit. If I select 16-bit, the file description (under the file name) changes to 16-bit but on re-exporting, closing and reimporting, it's 32 again and the file size is unchanged. (Same happens if I save as .wav.)

Any ideas?

[steve]

If your default "Quality" setting is 32 bit, then files will be converted to 32 bit on import, regardless of what the bit depth of the file is.

To make a smaller file you need to set the MP3 format to a smaller "kbps" setting.
To do that in Audacity 1.2.6 you need to go into Preferences and find the MP3 settings (this is much easier in Audacity 1.3.12 as the settings can be changed by just clicking the "Options" button in the Export screen).

Lower "kbps" will produce smaller files, but lower sound quality.

[fjchild]

Ok. The default bit rate was 192; I changed it (eventually) to 128 and the file sample format left at 32. So the final file size under 300 and still stereo. It didn't seem to matter, stereo or mono. !!

Thank you very much.

[steve]

It didn't seem to matter, stereo or mono. !!

No, it won't make any difference to the size, which is what I tried to explain here:

Not exactly. When you export in a compressed audio format such as MP3, the "compression settings" determine how many "bits" of data (digital 1's and 0's) are used for each second of audio. If you export as MP3 at 128kbps (128 thousand bits per second), then it doesn't matter if it's a mono or a stereo track, the file will still use 128kb for each second of audio.

Where the benefit of converting to mono comes in is in the trade-off between file size and sound quality. The more you compress the audio, the less "bits" are used for each second of audio. This is achieved by throwing away some of the "less important" data. So compressing to 64kbps means that 64 thousand "bits" are used for each second of audio, which will produce a file that is about half of the size of the same audio compressed at 128kbps, but because a lot more data has been discarded the sound quality will be less good. The advantage of converting to mono is that you start off with less audio data (one audio channel rather than two) which means that you can compress to 64kbps and have almost the same sound quality as a 128kbps stereo file, but in only half the file size.

[bgravato]

Another option for voice only tracks is to export in speex rather than mp3. Speex is an audio format specially optimized for speach. It's free and it's open source and it's really good... It can produce very small files at very low bitrates, with very acceptable sound quality... The draw back is that I'm not sure if it is natively supported by the most common audio players... (and by this I mean windows media player, because all the other "decent" audio players should support it...)