Optimal mp3 quality for FM Stereo Recording?

Shredder wrote on 1/10/2003, 9:19 AM

Hi,

I need to archive some FM Radio broadcasts and I want to save the programs in the highest possible quality, but without being overkill for the source media (an FM broadcast).

I have read that a 22,050 kHz 16-bit stereo recording is higher quality than an FM brodcast, so I'm assuming that should be opitmal and that anything higher would be overkill. Can I even go lower?

Finally, space is a big concern, so I want to compress these to mp3s. I have read that 112kbps is comparable to FM, but cannot find any details if that's 112@44.1 or 112@22.050, stero/mono etc. -- so I don't know if i should trust this.

So, does anyone out there have any technical expertise on this? What should be my optimal settings to balance space and quality?

Thanks,

Jon

Comments

Cold wrote on 1/10/2003, 12:47 PM

I think you may be missing an important point here. Any time you convert files to mp3 or any other lossy codec you are doing further damage to files that may have not been pristine in the first place. What they mean by fm radio quality is that a cd quality recording will have the same detail/sound as fm radio if you use this setting (and this is not nescessarily true either). So if you take an fm radio quality recording and convert it to mp3 the recording will suffer further degradation. If you really insist on compressing your recordings, look at a lossless format such as perfect clarity audio, There was a discussion happening about pca in a different thread, I'll add a location in my next post.
Steve S.

Cold wrote on 1/10/2003, 12:59 PM

This is the middle of a thread, but not a bad starting point.
http://www.sonicfoundry.com/Forums/ShowMessage.asp?MessageID=142687&Page=2

Chienworks wrote on 1/10/2003, 2:10 PM

7Once upon a time a wise person said, "a difference which makes no difference is no difference." If you are indeed only archiving and not planning on reusing the files for additional editing then you can probably get away with a lot more compression. 128Kbps is generally considered very listenable. I suggest you try saving a few files at 32, 64, 96, 128, and 160Kbps, then have a few other people do a "blind listening" test to see what they consider acceptable. If they can't tell the difference ... then what difference does it make?

Rednroll wrote on 1/10/2003, 2:40 PM

Damn this kills me!!! It probably would have taken you less time to do your own blind test and answer your own question just by recording the material and using the MP3 templates in the Save AS menu, than posting this question and waiting for replies.

Record the audio as a .Wav of 16bit 44.1Khz Stereo file, then render that to an MP3 format of different bit rates and then see what you consider acceptable. Generally I use 160Kbs 44.1Khz Stereo rendering and find it gives me the best quality to size ratio. 128Kbs says it is CD quality, but I find on some material I can hear a bit of phasing going on, so I went up one knotch to 160Kbs and it's better. Don't bother with the mono settings, because this does not save on the file size.

Cold wrote on 1/10/2003, 2:49 PM

This is a fair point, if you are archiving them with the intention of never touching them again besides maybe for casual listening, compress away, sort of like saving the work to cassette tape though, its cheap but perhaps not the best way to store something for posterity. Blank CDs are cheap, save your recordings to these without compression, and leave the files on your hard drive in a compressed form for easy access. I guess, in the end, it just depends how important these recordings are to you. Steve S

Geoff_Wood wrote on 1/10/2003, 3:00 PM

As FM bandidth can approach 15KHz, 22K sampling will not do it justice in the Linear PCM scenario. So 16/44K1 is called for. But when encoded to mp3,so much more is lost that it become subjective.

I suggest doing the initial recordings at 16/44K1, then experiment with mp3 conversion at different encoding rates. I guess 160kbps may be the one you choose. Bigger files and still audible artifacts (more that a godd quality FM broadcast) , but significantly better than the more common 128kbps.

geoff

Shredder wrote on 1/10/2003, 4:47 PM

Thanks for all your responses.

A couple issues:

1. I can't record at 44.1 kHz because that creates files larger than 2gb which is a wav format limitation (not a fat32/ntfs issue). While vegas can potentially work around this, i need to auto-record on a schedule which vegas cannot do.

2. I need small files, since a 4.5 hour broadcast runs about 253mb for 128kbps. I will be recording every weekday for many weeks so that'll start eating up drives and cds. I'd like to shoot for 1 cd/week, which is roughly 66kbps

3. I will not be editing these in the future. they are strictly for personal archive purposes.

I guess i'll have to do 64kbps. The question there is a 44.1 @ 64 going to be lesser quality then a 22.050 @ 64 etc.

Rednroll wrote on 1/10/2003, 5:59 PM

For the recording side 4.5 hours of 44.1Khz 16 bit stereo comes out to be about 2.5 Gig. You could easily make that 2 gig limitation by dropping the sampling frequency to 32Khz instead of the 22Khz and still have the full spectrum. You could also drop that size in half by recording mono instead of stereo, if this is for just personal backup use, therefore your 2.5gig becomes 1.25gig, and then if you drop down to 32Khz you could probably get that down to 900 Meg, and then goto MP3 at 128Kps which will leave you with a file size around 180Meg per day. That's about 900 meg for 5 days and you could go purchase some 99minute CDRS, which will about fit that perfectly.

Ouch...my head is starting to hurt from all the math.