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Topic: FM Vs AAC  (Read 1509 times) previous topic - next topic
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FM Vs AAC

Hello Guys I have A question what is the equivalent Bitrate of AAC to get the same quality as FM ? Thanks in Advance.

Re: FM Vs AAC

Reply #1
There isn't a magic bitrate that will make it sound like FM no matter how low you go. Lossy compression degrades the audio differently rather than simply reducing the bandwidth of the signal.

When we look at the raw bandwidth numbers for uncompressed audio:
CD Quality is Stereo, 16bit, 44.1Khz sampling rate
FM Quality is Stereo, ~12bit, ~32Khz sampling rate
Simply converting CD Audio to ~12bit, ~32Khz won't give you the typical FM radio sound since the radio stations usually filter the signal before sending it out, stuff like dynamic range compression and limiting.

I would say whatever bitrate can achieve transparency for a 32Khz sampling rate input. This is something you will have to test for yourself. It is probably going to be a bitrate that is very close to what was used for 16bit, 44.1Khz input.

However this doesn't mean that when you use that same bitrate for 44.1Khz, 16 bit input that you will get "FM quality".

Re: FM Vs AAC

Reply #2
FM is like a passband PCM filtered from 50 Hz to 15 kHz according to this website. And dynamic range of 50 db according to this website. But now almost all radio stations encode as digital before broadcast as analog.

Therefore, FM is a PCM of 30 000 samples per second and stereo bit depth between 8 and 9 bits or lesser according to this website.

Re: FM Vs AAC

Reply #3
FM is like a passband PCM filtered from 50 Hz to 15 kHz according to this website. And dynamic range of 50 db according to this website. ...
It is no problem for FM transmission to modulate from < 20 Hz to > 15 kHz.
And if you have a good signal without reflections, the dynamic range is well above 60 dB, using a good tuner even more than 70 dB.

Re: FM Vs AAC

Reply #4
FM is like a passband PCM filtered from 50 Hz to 15 kHz according to this website. And dynamic range of 50 db according to this website. ...
It is no problem for FM transmission to modulate from < 20 Hz to > 15 kHz.
And if you have a good signal without reflections, the dynamic range is well above 60 dB, using a good tuner even more than 70 dB.
https://en.wikipedia.org/wiki/FM_broadcasting
"The (L+R) signal is limited to 30 Hz to 15 kHz to protect a 19 kHz pilot signal. The (L−R) signal, which is also limited to 15 kHz, is amplitude modulated onto a 38 kHz double-sideband suppressed-carrier (DSB-SC) signal"

"for a given RF level at the receiver, the signal-to-noise ratio and multipath distortion for the stereo signal will be worse than for the mono receiver"

https://en.wikipedia.org/wiki/FM_broadcasting#/media/File:RDS_vs_DirectBand_FM-spectrum2.svg

Re: FM Vs AAC

Reply #5
Try your local classical music station (if your area has one), plenty of stereo hiss there compared to your local top40 station that cranks the volume level and manages to hide the hiss a lot better.  Neither is a great listening experience for me, it's either deal with the slight background hiss or deal with the hyper sophisticated compression to over come said hiss.

 

Re: FM Vs AAC

Reply #6
Back in my antenna reception days the closest transmitter was 30 km away, rated 100 kW power for each station, also a classic one. Hiss was of course audible, but not worse than a cassette recorder using Dolby B.

In real world there is an upper limit of 15 kHz, even though there were at least two tuners which had an active pilot suppression an so might have handled more than this - if it came in.