REDUCING MP3 FILE SIZES

[wsws]

Can I reduce the file size by lowering the sound quality of an MP3 file?

The answer to my question must be posted in plain English somewhere at this web-site, etc. After hours of searching, I have not been able to find it.

From the Audacity Toolbar menus, I selected the EDIT, AUDACITY PREFERENCES, FILE FORMATS tab. I do not know which bits, kilo-hertz, etc. settings to choose. Audacity's interface is more intuitive once one understands it.

I enjoyed using Audacity to remove the commercials from a one hour long radio talk show. I reduced a 75 MB MP3 file to about 35 MB. Since the sound quality of talk need not be as high as for music, would a file size of about 5 or 10 MB be adequate? Please tell me how.

[kozikowski]

There are a number of tricks to doing this, but one big one is peeling off stereo. I routinely pull down a stereo NPR show and push it into one channel mono and then compress it for my iPod. It works very well, and the file sizes can be really tiny. I really don't care that Scott Simon isn't in my left ear any more.

There are billions of adjustments for MP3, but only one or two critical ones are made available for you in Audacity. Generally, the lower the bitrate, the worse the show sounds. You need to try it, because sometimes stuff that's OK to you may be complete trash to me. You can get an MP3 compressor to grind a track down to almost nothing, but it will sound seriously bubbly if you do that. Several of us found that 32K is the minimum bitrate for a mono show. Past that and the sound damage goes way up.

If you were in Mac/iTunes world, you could use Apple AAC which is a version of H.264. That will give you between two and five times smaller files for the same quality sound. MP3 (formally, MPEG1, Layer III) has been around for a very long time.

There is no No Damage MP3. MP3 is a destructive compressor. It rips the track apart and destroys pieces it thinks you're not going to miss anyway. It's pretty cool how it does it, but the upshot is that it can turn a $6000 violin into a $300 violin--mostly because a $300 violin compresses better. So it doesn't just delete all the flutes or anything like that.

If you can't tell the difference between violins, then high compression may not bother you.

Koz

[kozikowski]

<<<would a file size of about 5 or 10 MB be adequate?>>>

"Please tell me the best settings....."

The question that has no answer. All modern compressors, video and audio, know about content. If your content is really simple and plain and mono, then the file sizes can be really small and sound just fine. If you have a totally full quality stereo show with sub bass, Aeolian-Skinner pipe organ, massive orchestration, and two kettle drums, then the file sizes are going to shock you. That's why the programs can't tell you the file sizes ahead of time. They won't know until after they "sniff" the show.

Koz

[wsws]

I thank Kozikowski for his kind response to my Dec 09 post about reducing the size of an audio file.

I routinely pull down a stereo NPR show and push it into one channel mono and then compress it for my iPod. It works very well, and the file sizes can be really tiny.

How do you do that, please? I need step by step instructions. I downloaded Audacity about a week ago, and read the instructions in the Help file. All I have been able to do so far is to delete some commercials from a radio talk show.

None of my following experiments reduced the file size:

ATTEMPT #1: From the Audacity Toolbar menus, I selected the EDIT, AUDACITY PREFERENCES, QUALITY tab. I did not change any of the other default settings. I lowered the "Default Sample Format" from 44100 Hz (the default setting) to 11025 Hz and saved the file, but the size of a 38 MB audio file remained the same. I restored the default setting.

ATTEMPT #2: I lowered the "Default Sample Format" from 32 bit float (the default setting) to 16 bit float. I did not change any of the other default settings. I saved the file, but the size of a 38 MB audio file remained the same. I restored the default setting.

ATTEMPT #3: Via the Audacity "Track Pop Down Menu", I split the two tracks and deleted the upper (left) track. I changed the setting from Stereo to Mono. The size of a 38 MB audio file remained the same after I saved it, so I undid all of these changes.

ATTEMPT #4: Via the Audacity "Track Pop Down Menu", I selected SET SAMPLE FORMAT from the sub-menu. I changed the setting from a "32-bit float" to "16-bit", and saved the file. The sound quality was reduced, but not the size of the file. I changed the setting back to a "32-bit float".

I have not yet experimented with the options displayed under the AUDIO I/O tab; the default setting was RECORDING, CHANNELS, 1 (Mono).

[kozikowski]

None of those attempts actually changed the show. If you had exported the show as a WAV file and inspected it, it would be exactly the same down to the sample rate and bit size. Audacity is a little wacky that way.

If nobody else drops in, you need to wait until I have a little more time to deal with this,

Koz

[wsws]

I thank Kozikowski for his immediate response to my Dec 11, 2007 post about my efforts to reduce the size of a 38 MB MP3 file.

you need to wait until I have a little more time to deal with this,

I shall. I am a grateful and patient learner. Must the parameters be set before the audio file is imported into Audacity?

[kozikowski]

This is a slightly changed version of instructions by Julian Yap.
http://www.julianyap.com/wiki/Convert_S ... h_Audacity


--From Stereo Show to Mono MP3--

Black Down Arrow (on the left) > Split Stereo Track

Black Down Arrow > Mono (each track)
+/- slider > -6dB (each track)

Project > QuickMix

Preferences > File Formats > MP3 Export Setup > Bit Rate
--Change as often as you like.

File > Export As MP3


Note that there's no instructions for reducing the quality of the show ahead of the compression. That's actually the reverse of what you should be doing. Destructive compressors like MP3 work much better from the highest quality show you can deliver. There is a provision in MP3 for dual-pass compression, but I think you can only do that in 1.3.x versions of Audacity. It compresses the show and then goes back and clears up some of the mistakes. It takes a lot longer, but produces a much better show.

Extra points for bookkeeping. Build the compression into each filename. piano2-32K.mp3. otherwise you'll never remember what you did on each test.

Koz