Head-Fi.org › Forums › Equipment Forums › Sound Science › Radio Bitrates?
New Posts  All Forums:Forum Nav:

Radio Bitrates?

post #1 of 29
Thread Starter 
What is the equivalent bitrate to a signal of FM radio? is it constant or does each station pick theyr sound quality? it seems to me that some radios sound better than others. before you say that its because the transmitters are further away, dont. The two radios in question share the same transmiting pole thing.
post #2 of 29
Quote:
Originally Posted by NoHands View Post
What is the equivalent bitrate to a signal of FM radio? is it constant or does each station pick theyr sound quality? it seems to me that some radios sound better than others. before you say that its because the transmitters are further away, dont. The two radios in question share the same transmiting pole thing.
You can estimate the approximate Audio information [1] content of FM by using the bandwidth and dynamic range. FM pretty much tops out at about 15K and the dynamic range is about 70db. Each bit represents approx 6db so we need just under 12 bits and a sampling rate of 30K.

Thus = 12 x 30,000 x 2 (2 channels) = 720Kbps (CD is 1411kbps) that is uncompressed.

1. FM transmission is somewhat more complex than that with carriers and what have you but we are not interested in that level of accuracy.
post #3 of 29
This question is also complicated by the fact that virtually all radio stations nowadays use lossy compression extensively in their production process. So from a quality standpoint, it really could be far worse than you might think.

Jukebox software using Musicam/MP2 (!) has been standard for quite some time now - I remember seeing a Windows box with a sound card control all the programming on a station in 1992 or so, with a 9GB RAID array for music storage. NPR, if I'm not mistaken, still uses MP2 for its satellite feeds. The BBC has taken great pains to ensure a lossless signal path to the station, although it's typically compressed to hell on DAB anyway.

Nowadays I understand that syndicated content, and even individual music singles, are transferred over FTP, typically using MP3 or something of that nature. And it's entirely unclear what bitrates and encoders they're dealing with.

Ultimately, this hobbles the sound quality of HD Radio. The bitrates I've seen for it are great, and soundly beat XM/Sirius down - but virtually everything played on radio is already lossy compressed. So digital FM radio generally requires a transcode! Not good.
post #4 of 29

the reason why some radio stations sound better is some are using CDs others are using MP3s

post #5 of 29
Quote:
Originally Posted by Publius View Post

This question is also complicated by the fact that virtually all radio stations nowadays use lossy compression extensively in their production process. So from a quality standpoint, it really could be far worse than you might think.

Jukebox software using Musicam/MP2 (!) has been standard for quite some time now - I remember seeing a Windows box with a sound card control all the programming on a station in 1992 or so, with a 9GB RAID array for music storage. NPR, if I'm not mistaken, still uses MP2 for its satellite feeds. The BBC has taken great pains to ensure a lossless signal path to the station, although it's typically compressed to hell on DAB anyway.

Nowadays I understand that syndicated content, and even individual music singles, are transferred over FTP, typically using MP3 or something of that nature. And it's entirely unclear what bitrates and encoders they're dealing with.

Ultimately, this hobbles the sound quality of HD Radio. The bitrates I've seen for it are great, and soundly beat XM/Sirius down - but virtually everything played on radio is already lossy compressed. So digital FM radio generally requires a transcode! Not good.

Your information is quite dated.  The need for lossy compression for digital audio storage in broadcasting went out in the late 1990s.  Musicam...never really got started.  MP3 is really MP2 layer 3.  We used high-rate mp3 when large SCSI HDDs were expensive.  Those days are long gone.  In the early 2000s the "norm" was uncompressed broadcast .wav files for music libraries, possibly .mp3 for commercials because they arrived for air-play done that way already.  

 

Today when MP2 Layer 3 (MP3) is used, it's generally at 256Kbps or higher, and results in files indistinguishable from the original.  There are situations where low-rate compression gets aired, but it's not the norm any more, and isn't why radio stations sound different from each other.

 

Studio-transmitter links are minimally lossy at worst, more typically lossless today.  The "hobbling" of HD Radio (no such thing as digital FM, sorry), is in that the total available bandwidth can be divided into several sub-channels.  If HD1 only is used, the results are pretty darn transparent.  If the station elects to use many sub channels, there must be progressively higher bit-rate reduction, with the highest quality still presented on HD1, but never as good as when that's the only digital stream transmitted. 

 

It would not be correct to say, "virtually everything played on radio is already lossy compressed", however.

 

The one mandatory transcode is into an HD Radio transmitter.  But that transcode doesn't hit analog FM.  The presence of an HD Radio signal does degrade analog FM slightly, but not in terms of transmitted audio bandwidth on analog FM.

 

Far and away, the most damage done to a broadcast signal occurs in the broadcast processing chain, not the storage and transmission of the audio.

post #6 of 29
Quote:
Originally Posted by nick_charles View Post
 
Quote:
Originally Posted by NoHands View Post
What is the equivalent bitrate to a signal of FM radio? is it constant or does each station pick theyr sound quality? it seems to me that some radios sound better than others. before you say that its because the transmitters are further away, dont. The two radios in question share the same transmiting pole thing.
You can estimate the approximate Audio information [1] content of FM by using the bandwidth and dynamic range. FM pretty much tops out at about 15K and the dynamic range is about 70db. Each bit represents approx 6db so we need just under 12 bits and a sampling rate of 30K.

Thus = 12 x 30,000 x 2 (2 channels) = 720Kbps (CD is 1411kbps) that is uncompressed.

1. FM transmission is somewhat more complex than that with carriers and what have you but we are not interested in that level of accuracy.

While I understand why the analysis is desired, you can't directly compare an analog transmission channel with a digital one.  Bandwidth in FM is limited by the presence of the 19kHz stereo pilot at -20dB (re 100%).  While everybody thinks that means there's a 15KHz lpf in there, how we build that filter today means bandwidth a few KHz above 15 in most cases.  The filter used to be a five to seven pole filter with as little passband ripple as possible, then later it became phase compensated, and now it's digital.  

 

However, that's only the hard upper response limit.  There's another one, much more significant.  Because of pre-emphasis (+17dB at 15kHz re: 400Hz), and yet we must still limit modulation to 100% at all frequencies, we don't have a full output bandwidth to 15kHz.  This dictates the use of special high frequency processing, and affects the high frequency performance dynamically.  

 

Because of this, it's not possible to accurately equate FM performance with a digital bit-rate.  When you throw in stereo noise performance, the comparison is fuzzy at best. 

post #7 of 29
Quote:
Originally Posted by drtechno View Post
 

the reason why some radio stations sound better is some are using CDs others are using MP3s

Very few stations still air CDs directly.  Very few stations still store music as .mp3.  There's simply no need to do either in most cases.  

 

Again, all other aspects being equal, the difference in audio quality of FM stations centers on their differences of on-air audio signal processing.  Those differences are huge, and are there by intent and design.  

post #8 of 29

The radio stations around here run mp3s because its easy to set up a play list and automate it.

post #9 of 29
Quote:
Originally Posted by pinnahertz View Post
 

Your information is quite dated. ...

 

Noticed the post date of the comment you replied to?

 

Not to you specifically - but If there is still interest on this topic, I think a new thread is probably more useful than necro-posting

post #10 of 29
Quote:
Originally Posted by ClieOS View Post
 

 

Noticed the post date of the comment you replied to?

 

Not to you specifically - but If there is still interest on this topic, I think a new thread is probably more useful than necro-posting

The thread had activity a mere few hours before I posted.  It was that activity that called it to my attention.  That, and the proliferation of misinformation. 

post #11 of 29
Quote:
Originally Posted by drtechno View Post
 

The radio stations around here run mp3s because its easy to set up a play list and automate it.

No professional station would run .mp3 files just for that reason.  Broadcast automation software doesn't just build an .mp3 playlist.  Music scheduling software is far more complex,  dealing with frequency of play, relations between songs, song type and style, popularity, and dozens of other parameters.  The entire on-air playback system doesn't depend specifically on file type, other than it have tagging capability.  Then the music selection software integrates with commercial scheduling and traffic (billing) to produce a total log with places for live announcements, etc.  

 

Again, the ONLY reason to use an .mp3 is the smaller file size.  If they are used at all, they will be at a high bit rate where the lossy compression has no audible impact.  Unless, of course, we're talking about high school and college stations, then all bets are off.  I know of one that uses iTunes on air!  But that's not what the pros do. Not even close.

 

And, .mp3 is absolutely NOT the reason stations sound differently (or badly). 

post #12 of 29
Quote:
Originally Posted by ClieOS View Post
 

 

Noticed the post date of the comment you replied to?

 

Not to you specifically - but If there is still interest on this topic, I think a new thread is probably more useful than necro-posting

no I didn't.

 

 

looks like I found the sarcastic antagonist here though.... the love I feel from this person... :  Pinnahertz

post #13 of 29
Quote:
Originally Posted by pinnahertz View Post
 

No professional station would run .mp3 files just for that reason.  Broadcast automation software doesn't just build an .mp3 playlist.  Music scheduling software is far more complex,  dealing with frequency of play, relations between songs, song type and style, popularity, and dozens of other parameters.  The entire on-air playback system doesn't depend specifically on file type, other than it have tagging capability.  Then the music selection software integrates with commercial scheduling and traffic (billing) to produce a total log with places for live announcements, etc.  

 

Again, the ONLY reason to use an .mp3 is the smaller file size.  If they are used at all, they will be at a high bit rate where the lossy compression has no audible impact.  Unless, of course, we're talking about high school and college stations, then all bets are off.  I know of one that uses iTunes on air!  But that's not what the pros do. Not even close.

 

And, .mp3 is absolutely NOT the reason stations sound differently (or badly). 

 

when I went for the a job at the radio station they they told me about putting songs and commercials in a play list was one of my jobs as a programming engineer.

 

so do you like to argue for sake of arguing pennahertz? Life is really too short for that.

post #14 of 29
Quote:
Originally Posted by drtechno View Post
 

 

when I went for the a job at the radio station they they told me about putting songs and commercials in a play list was one of my jobs as a programming engineer.

 

so do you like to argue for sake of arguing pennahertz? Life is really too short for that.

...and one of my jobs as a Chief Engineer for numerous stations for the last 45 years is to know the difference between technical fact and nonsense.  I'm sure you put songs into a playlist.  That has nothing to do with the use of .mp3 or not, which also has nothing to do with how the station sounds.  Unless, of course, the entire operation was extremely low-end, and lacked technical guidance.  

post #15 of 29

They run 3 different FM radio stations. It didn't look low end.

New Posts  All Forums:Forum Nav:
  Return Home
  Back to Forum: Sound Science
Head-Fi.org › Forums › Equipment Forums › Sound Science › Radio Bitrates?