Re: Audio quality degradation over FM transmission

kristian.hermansen@xxxxxxxxx wrote:

Ian Stirling wrote:

For a good signal, pretty much the only thing that you could notice is that
the bandwidth is a bit lower, as the FM signals bandwidth is about 15Khz,
compared to the CD bandwidth of about 20Khz.



Will I lose the low or high frequency bands?  I mean, will I get less
bass or less treble?  What is the frequency window?


FM radio is much, much higher quality than 64K, if you're in decent signal
area, I'd go so far as to say that a good quality signal is usually better
quality than 128K.



Why can it not be CDDA quality?  For instance, why can't a CD be
streamed over the radio without loss in quality?  The frequency of the
music is 44.1 KHz and the FM frequency is between 88-108 Mhz -- which
is a magnitude of 10^3 apart.  I'm confused :-(


As to "degradation of sound quality", you're not using a FM transmitter
plugged into a MP3 player are you?



Yes, I am.  Got me :-)


These are generally designed down to a price, not up to best audio quality. 


What if I had a high-quality transmitter?

Kristian Hermansen

Nope, the MP3 player doesn't have that quality. The reason there are MP3s is because of compression, they eliminate some of the 'unneeded' data that is stored on the CD so that it will take up less space. This compression means that there is more noise and less dynamic range in an MP3 than the original. You also loose some of the highs.

Next, you have your MP3 player. When he said designed down to a price, he was talking about the MP3 player, not the transmitter. They often do not have the 'best' audio stages, being just good enough to not sound too crappy, usually. Now, you take this already distorted, noisy source data, the MP3, put it out from the so-so audio out of an MP3 player, couple it (usually badly, with impedance mismatches and other signal degraders) into your FM transmitter with a MAXIMUM frequency range or probably 15K, and you will hear a lot poorer music than the original CD. Such is engineering.

Charlie
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Relevant Pages

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