FM Radio Compression Question

[ernstinen]

Hey All,

Most of us know that powerful FM stations like here in L.A. use the top-of-the-line monster compressors to squash the signal before it's broadcast. But here's my question: Even knowing that, why (at least in my car stereo) do FM broadcasts sound SO much louder than CD's? Let's say I've got a powerful FM station on, and my volume level is 10. In order to get CD's (whether they're commercial, or my own mixes) as loud as the FM signal, I have to turn up the volume maybe 3 TIMES louder!

Do you guys and gals find the same thing with your car stereos, or is it just my CD player/receiver?... It's really shocking when I master a CD of my own mixes as loud as humanly possible and go listen to it in the car, the radio is on, and when I put in my CD (or a commercially bought CD) I have to turn the volume WAY up!

Does anyone know technically what the answer to this question is?

Thanks in advance,

Ern

[Len911]

Well because radio is mostly listened to in a car, and the ear is most sensitive to 2-5k, it probably makes sense to condition the audio a little differently. First priority is the 2-5k range so you can hear what they and the advertisers are saying clearly. Bass frequencies are probably kept lower, small space and to keep the door panels and dash from shaking to pieces, and with all the window area, high frequencies are probably kept lower because of the excessive harshness. Plus all the road and engine noise, so they need to compress the 2-5k so it is above the noise. If all frequencies were the same loudness, you would turn the radio down when the doors rattled or harsh reflections from the glass, and not hear the vocals as well. In an office environment, the crap speakers probably don't handle bass that well, and the radio is usually turned down, but you can still hear the voice clearly.

If you mastered the cd in a car instead of a quiet and larger space, maybe you'd end up with something approaching the FM signal??

How much they limit low and high frequencies can probably be determined by the difference you hear between the FM and the cd, it might not be that much, the real difference is probably in the 2-5K range, as you have already in a round about way indicated.

[mojobone]

The answer is in your first sentence, Ern. There's a little more to it, though, cuz radio stations stopped using CDs years ago. That said, the original source is likely CD grade or better, but what you hear has first been data-compressed, decoded and then run through a series of processors including but not limited to (see whut I did, there?) a multiband compressor, graphic and/or parametric EQ, look-ahead limiting, at least one analog or digital broadcast limiter with some very specific metering capabilities and something called a phase rotator before hitting an FM transmitter. Some stations will include a de-esser, because the EQ profile that helps them cut through the din can make the trebles harsh. If you listen to most commercial FM stations on good equipment you can clearly hear artifacts of this long embiggening process; it ain't purty. You may have a mastering preset that's way over the top, named something like "Punch Processor" or "Big Time"; that's kinda what radio does, AM too, though they have less frequency spectrum to work with.

[andygabrys]

In your car stereo if you compare one commercially produced CD vs. yours - that is your volume answer right there and who cares about the FM radio

[ernstinen]

the real difference is probably in the 2-5K range.

Yeah, I get that. But that was more in the days of AM radio, where car speakers really only reproduced midrange frequencies. Certain engineers/producers took advantage of that to make their masters louder than other records, like The Beatles. Their guys limited/compressed the crap out of every track (which were all midrangey to begin with), and then on mixdown/mastering, they used tons of compression on top of that. You can actually HEAR the compressor kick in and release on their early records!... But today's mixes, because the frequencies below 60 Hz don't have to be rolled off anymore (they use to do that so the turntable stylus wouldn't jump out of the record grooves), digital mixes/masters have TONS of bass and highs on them. And good car stereos can reproduce them. So an FM station doing a midrange bump probably doesn't happen as much (or at all) like in the "old days!"

My 2 cents,

Ern

[ernstinen]

The answer is in your first sentence, Ern. There's a little more to it, though, cuz radio stations stopped using CDs years ago. That said, the original source is likely CD grade or better, but what you hear has first been data-compressed, decoded and then run through a series of processors including but not limited to (see whut I did, there?) a multiband compressor, graphic and/or parametric EQ, look-ahead limiting, at least one analog or digital broadcast limiter with some very specific metering capabilities and something called a phase rotator before hitting an FM transmitter. Some stations will include a de-esser, because the EQ profile that helps them cut through the din can make the trebles harsh. If you listen to most commercial FM stations on good equipment you can clearly hear artifacts of this long embiggening process; it ain't purty. You may have a mastering preset that's way over the top, named something like "Punch Processor" or "Big Time"; that's kinda what radio does, AM too, though they have less frequency spectrum to work with.

Now, that makes more sense to me! I'd like to get a dB meter and see how much louder FM is compared to CD's on my car stereo.

I was marveling at how BRIGHT certain high-res files ("Nevermind" by Nirvana) sounded on my car stereo (especially the guitars) when I was trying to figure out how to EQ a Metal track that I just submitted. The guitars sounded like buzz saws, definitely not the warm tube sounds of more old school rock. (I tend to think Cobain used some solid-state system for his guitars in the studio). But then I noticed that when I started driving (like Len alluded to), that obnoxious upper midrange kind of went away due to road and wind noise. It actually sounded better than listening while parked!... But how many of us take a master CD of our own music out to the car and drive on the freeway to listen to it? I don't. Maybe I should LOL!

Ern

[ernstinen]

In your car stereo if you compare one commercially produced CD vs. yours - that is your volume answer right there and who cares about the FM radio

There ya go! I was just wonderin', actually. That's certainly WAY more important.

One "commercially produced" CD that baffles me is "Kid A" by Radiohead. That opening track is SO loud, but if you think about it, it's just a solo keyboard for the most part. I'm sure they squashed the crap out of it, and there aren't any other competing frequencies to worry about.

I think I'm going to buy a frequency analyzer and see how they bump the EQ of the louder CD's. I've always used my ears, but maybe they're shot by playing in loud rock bands for so many years!

Ern

[mojobone]

Now, that makes more sense to me! I'd like to get a dB meter and see how much louder FM is compared to CD's on my car stereo.

I was marveling at how BRIGHT certain high-res files ("Nevermind" by Nirvana) sounded on my car stereo (especially the guitars) when I was trying to figure out how to EQ a Metal track that I just submitted. The guitars sounded like buzz saws, definitely not the warm tube sounds of more old school rock. (I tend to think Cobain used some solid-state system for his guitars in the studio). But then I noticed that when I started driving (like Len alluded to), that obnoxious upper midrange kind of went away due to road and wind noise. It actually sounded better than listening while parked!... But how many of us take a master CD of our own music out to the car and drive on the freeway to listen to it? I don't. Maybe I should LOL!

Ern

I've had the rare privilege of hearing my music on the radio, and I think it's worth delving into a bit if we entertain the notion that such could happen to nearly anyone, these days. I think also that it's a worthwhile exercise to reverse engineer one's local FM stations and their formulas, (Particularly if you live in a medium to large media market) but you needn't buy a frequency analyzer if you have a laptop, interface and measurement mic handy. EQ matching software would make the job even easier, cuz you really only need an SPL decibel meter and something that reads peak and average levels on a single scale so you can measure how much squash is going on. Or you could use a handy recorder to capture some road noise at various speeds for later analysis.

I'm not sure if many useful comparisons between CDs and broadcast FM can be made when it comes to frequency spectra, but your car is a heckuva good resource when it comes to mastering decisions and road noise is the primary reason. If you take out all the harsh frequencies, there might not be enough punch for the music to cut through the wind/road noise. You can probably forget trying to measure in a convertible...

[ernstinen]

I've had the rare privilege of hearing my music on the radio.

So have I --- in my earlier days of using compressors. A song of mine was broadcast on an internationally syndicated radio show, and I was so excited to listen to it that night.. What I found is that I used TOO MUCH compression on my mix! Compression is something you can't "undo." So, too much compression on top of the radio station squashing the hell out of it = no dynamics. I'm of the opinion that brickwall compression like some engineers use is unmusical. And I did the same thing, but that's because I was new to the whole thang. I don't do that anymore; if the meters aren't moving 4-5 db, you're overdoing it. Just my opinion, of course!

Ern