I hope this is the right section to pose this issue. I'm trying to find the best suitable settings to encode FM radio. For those radio broadcasts that utilize only voice, I'm thinking of going towards the Speex solution.

For all the others that happen to have songs as well, I'd like your advice. I found out in this page the following suggestion and since I'm not experienced enough in the field, I would need you comments...are they trustworthy?

"Many people have asked us how we use LAME together with FM-radio. Let's explain:
Before FM-stereo audio goes into the transmitter it's being filtered at 15 kHz (this - among other things - has to do with bandwidth of the transmitter-signal and stereo-keying at 19 kHz). All high frequency content above 15.* kilohertz will be cut off entirely. Some tuners will give you 15.7 kHz as their highest 'clean' audio frequency output, but most transmitters will not even air anything above 15 kHz.

Conclusively;

Encoding MP3 audio intended for analog FM-radio, or
encoding MP3 from audio that's recorded from analog FM-radio (tuner) outputs,
can safely be done using a commandline like:
(big to small mp3 file size)

lame in.wav out.mp3 -V5 --vbr-new -q0 -b96 --lowpass 15.4 or
lame in.wav out.mp3 -V6 --vbr-new -q0 -b96 --lowpass 15.4 or
lame in.wav out.mp3 -V7 --vbr-new -q0 -b112 --lowpass 15.4

with these you'll achieve around 10 times compression, while not losing anything from the FM original. Cutting off from 15 Kc will actually give you higher quality files, since there's more room left for other audio in the spectrum.

Logically, people then asked at what sample-rate they should record their FM-transmitted radio-audio.
If the anti-aliasing filter on a 32kHz digitizer is steeper than the original 15kHz filter used when the broadcasts were first made, it's possible that 32kHz digitization might lose a tiny bit of HF energy. The solution to this is to use no anti-aliasing filter before digitization (the material is already band-limited at 15kHz, so it doesn't need further filtering). An absolutely safe choice of sample frequency would be 38kHz, but this is almost never supported. If you are uncertain about the anti-aliasing of your soundcard (the SB Live! for example is safe to use with 32 kHz for FM-stereo mastering) use 44.1kHz, but both 44.1 and 48kHz are certainly overkill for FM-radio..."

Thanks a priori for your participation in the discussion.

Lowpass 15.4 uses a transition band of 15115 Hz - 15648. So you can feel sure that all the transmitted hf content is encoded, and at the same time you safely avoid encoding the 19 kHz pilot tone and other data streams.

Your information source is right about the lowpass, all FM stations use a very steep 15 kHz filter.

V6 or even V7 seems a bit too much to me, although V7 really sounds good when looking at the very low bitrate.

edit:
the presets use following transition bands without adding --lowpass xxx:
V5 15826 Hz - 16360
V6 15115 Hz - 15648
V7 14581 Hz - 14968 (resamples to 32 kHz)

So you don't even have to alter the presets.

What does it mean?

hmmm, and among many other things this is the reason why mr. J.T. is no longer a member in several MP3 communities:

When clicking the link you get this:



Strange guy he is

Honestly I can't say for sure...it's not my words in the first place!




Damn...I didn't even notice. I guess everybody understands how to get there anyway. He does seem kind of bilious though.

Btw...I had also checked out those technical informations regarding the frequencies that -V7 uses. What surprised me though is the fact that he chooses to use -b112 for a lower quality switch "-V7", although he used -b96 for better ones. It didn't make much sense to me.

Just for clarification...will the encoded mp3 use the internal "switches" of -Vx instead of -b112, -lowpass 15.4 and -q0 that the line demands?

http://www.hydrogenaudio.org/forums/index....howtopic=36672

http://www.hydrogenaudio.org/forums/index....showtopic=35272

http://www.hydrogenaudio.org/forums/index....st&p=109255

Makes me laugh remembering. Which is good considering how frustrating reading his BS is.

Thanks evereux. That thread clarifies everything!

I guess no need to research any further.