Subject:MP3 degradation

Posted by: John777

Date:10/13/2006 7:14:38 AM

I would like to know how quickly a MP3 file degrades with repeated editing.

Suppose I open a MP3 file in Sound Forge, make no changes, and save the MP3 file. Since MP3 is a lossy format, every time I edit and save the MP3 file there will be degradation because of the decoding and encoding of the MP3 data. I would like to know how quickly the MP3 quality degrades.

For example, if you encode a MP3 file at 128kbps and 44kHz. How many times can you edit (decode and encode) it before you hear a degradation?

Yes, I am aware that Perfect Clarity Audio (.pca) is a lossless format.

Thank you for your help.

Subject:RE: MP3 degradation

Reply by: Vocalpoint

Date:10/13/2006 7:57:40 AM

Maybe if you elaborated more on what you are needing to edit and why - the answer would be easier to explain.

Subject:RE: MP3 degradation

Reply by: John777

Date:10/13/2006 8:29:27 AM

I have a large number of MP3 talking head files. I need to sporadically edit them to remove segments of useless talking. Some files will be edited once others will be edited 5 or more times.

I am unclear how many times I can edit a file before there is a perceptible degradation in the sound quality say at 128kbps and 44kHz.

Thank you for the feedback.

Subject:RE: MP3 degradation

Reply by: rraud

Date:10/13/2006 10:23:16 AM

You should always edit in a "non-lossy" format, MP3 encoding should be the final step. That said, every time you edit and re-save an MP3 you lose quality, How much would depend on the MP3 file in question.. You will have to decide how much MP3 degradation is acceptable.

FYI - Always encode spoken word recordings in mono. All other factors being equal, a 64kbs mono file is about half the file size, but of equal quality as a 128kbs MP3 stereo file. Many recommend using the VBR (variable bit rate) setting for podcasts and the like, though a few older portable MP3 players had trouble playing the VBR MP3s.. If you are going to stream an MP3 over the internet, it is recomended to use the CBR (constant bit rate) setting. Again you will have to experiment and decide what's antiquate quality for either.

If archiving file size is an issue you can save your original file (before MP3 encoding) in the PCA format. Perfect Clarity Audio is data compressed but is non-lossy, it is however propriitory, and a SMS app. is needed to open it. PCA is simular to a Zip file but "zipping" an audio file yields limited data compression.

Subject:RE: MP3 degradation

Reply by: John777

Date:10/13/2006 11:09:10 AM

Ideally, all the files should have PCA format. However, PCA takes up a lot of space. With that in mind, it would be desirable to keep them as MP3 files. What I do not have a gut feel for is how often I could edit a given MP3, 128kbps, 44kHz file before you start to hear a degradation.

Thank you for the feedback.

Subject:RE: MP3 degradation

Reply by: Chienworks

Date:10/14/2006 5:25:09 AM

Some would say that zero times is too many; that saving in MP3 at all is too much degradation.

Others might say if you use a high enough bitrate, it won't matter.

YOU and your clients have to decide what works for you. No one else can answer that.

My suggestion is to save all the files as WAV or PCA until you know they are finished and ready for permanent archive. You can save MP3 versions for distribution, but don't delete the WAV or PCA version until you know for certain that you won't ever have to edit again. Always go back to the WAV or PCA version for editing.

Large files? Yes. Get more storage space. I see 320GB hard drives selling in the $100 range. If quality is important, this is a necessary expense. This needs to be a business decision. If your customers demand high quality with no repeated degradation then they can pay for your storage costs. This really isn't a negotiable item.

For cheap archival consider burning PCA files to DVD-R or DVD-RW. You can fit about 18 hours of CD-quality PCA files on a 4.3GB DVD, or about 36 hours if they're mono. Most DVD blanks are selling for under $0.40 these days, often much less in bulk. That's about a penny an hour! When OfficeMax dumps inventory i often pick up a 100 spindle of name-brand blanks for $10 or $12.

Don't edit MP3. Just don't do it.