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06-22-2008 Post does not mapped to Knowledge Tree
Romy the Cat


Boston, MA
Posts 9,540
Joined on 05-28-2004

Post #: 1
Post ID: 7652
Reply to: 7652
The Evolution (or Anti-Evolution) of FM Broadcast

A Seminar presented by Greg Burnett
at Audio Fest 2004, Colorado Audio Society

by John Haralson
October 9, 2004

Why are audiophiles interested in FM radio? Because the quality of FM audio was satisfying until stations began to compete with each other to maximize the loudness of their broadcasts – the "modulation wars", as Burnett calls the phenomenon. Burnett's argument is that, through injudicious use of audio compression, stations have "squashed" emotion from their broadcast music. He says the problem is particularly serious in Denver and Colorado Springs, where most stations process their audio heavily. Burnett observed that, as recently as 1997, FM audio standards in Los Angeles were much higher than in Denver. He attributes the heavy processing in markets such as Denver to "inbreeding and, in some cases, incompetence" amongst general managers, program directors and engineers: radio stations insist upon sounding as loud as they can, and they are willing to sacrifice fidelity and dynamic range to achieve that goal through compression.

To explain compression, Burnett began with a description of how FM radio works:

In the U.S., ±75 kHz deviation is the FCC standard for FM broadcasts. An assigned FM channel is 200 kHz wide, so the 75 kHz deviation on either side of the center of the channel occupies 150 kHz of the 200 kHz bandwidth. Other program sources, such as Subsidiary Communications Authority (SCA) and/or IBOC ("HD Radio), can extend modulation beyond the ± 75 kHz limits.

Another FCC-imposed standard is a 75 µs (microsecond) pre-emphasis curve. The purpose of the pre-emphasis during broadcast is to compensate for high frequency (HF) roll-off by the de-emphasis network in the user's radio receiver – de-emphasis intended to reduce noise and hiss at mid to high audio frequencies, thereby improving the signal-to-noise ratio (S/N) at frequencies to which the human ear is most sensitive. But Burnett says the pre-emphasis curve used in the U.S. (75 µs) is too steep – too aggressive – and therefore makes broadcasts susceptible to loss of high frequencies when modulation is compressed.

According to Burnett, in an ideal FM program, human voices register at perhaps 40 or 50% on a modulation meter. That leaves "headroom" (up to the 100% level) for sibilance and other high frequency information, which lends presence and emotion to music. Ample headroom also accommodates a wide, satisfying dynamic range.

However, today's FM stations, driven by pressure to sound louder than their competitors, compress their audio through processing, so that modulation is sustained nearly continuously at 100%. The result is degradation of music, as there is no headroom for high frequencies, and dynamic range is constricted.

In order to comply with FCC regulations, radio stations must process their audio by limiting high modulation levels. And they need to boost extremely low-level program material so that it will not be inaudible to listeners. But how much compression of these extremes is acceptable? To what extent should a station sacrifice the integrity of its program material in order to sound louder than its competitors?

Burnett acknowledges that the ideal compromise is a "tricky window". He demonstrated the extremes of no compression and heavy compression with a Orban 8000 processor, through which he fed the output of a compact disc player into a low-powered FM transmitter. A closed-circuit TV camera enabled the audience to monitor the processor's modulation meter. With no compression, and a wide range of modulation, Burnett described the music as "emotional, natural (with 'air'), addictive and wonderful." With heavy compression, and modulation constantly at 100%, the same musical source lacked emotion; it sounded "squashed, stressed, rolled-off, heavy and bulky." (The rolled-off sound he attributed to HF limiting, made worse by the pre-emphasis curve.)

Early processors consisted solely of 75 µs pre-emphasis and a wide-band automatic gain control (AGC) with a slow time constant, which reacted to dynamic changes gradually rather than instantly. But they did not produce the high modulation densities that today's broadcasters demand. Newer processors (from the 1970s and later) have added, as a minimum, a high frequency limiter and a clipper. Digital processors, now available, can "look forward" by delaying the program slightly, adjusting peaks even before they occur. Many other processing options are available, including "multi-band," which divides the audio spectrum into several bands and then compresses each band individually, but with adjustable correlation between the bands. These and other options give stations the ability to tailor their sound. The problem, according to Burnett, occurs when broadcasters "abuse" the adjustments of these options too far towards loudness at the expense of audio quality, failing to meet even the minimum expectations of their listeners.

Burnett acknowledges that a certain amount of compression in an FM broadcast is both necessary and desirable. But it is possible, he believes, for a processor to increase loudness without losing essential dynamic range and high frequencies; compromise must be accomplished very judiciously in order to satisfy the expectations of audiophiles – and even non-audiophiles. Most stations, he says, fail to get it right.


"I wish I could score everything for horns." - Richard Wagner. "Our writing equipment takes part in the forming of our thoughts." - Friedrich Nietzsche
06-25-2008 Post does not mapped to Knowledge Tree
niklasthedolphin


Denmark
Posts 2
Joined on 01-09-2008

Post #: 2
Post ID: 7671
Reply to: 7652
I won't argue about the technic
However...............in the old days when FM broadcasting was still analogue some of the programmes were worth listening to here in Denmark for the music and for the technical quality.

Today everything broadcasted is digitalized and when it's about live concerts of classical or jazz music at the best danish Radio is broadcasting comparable with 24/96 digital resolution.

But be aware that it matters more than the issue about digital vs analogue (as long as we are in the top level as 24/96 digital) what origin, what mastering, what studio/live sound-engineering set up is present. What Microphones are used, can the technicians control the level of dynamic compressing and equlization, how is the room accoustics, when in the chain wil it be AD converted, is further digital compressing needed etc. etc.

That is the reason for still leting my great Tandberg TPT 3001A stay in my setup...................for those special sendings with the rare combination of great music and great technical engineering. The latter is today becomming a very scarce handicraft or art.

"dolph"
06-25-2008 Post does not mapped to Knowledge Tree
Romy the Cat


Boston, MA
Posts 9,540
Joined on 05-28-2004

Post #: 3
Post ID: 7673
Reply to: 7671
Agree, it has nothing to do with digital vs. analogue debate.

Dolph,

As anything else in audio I do not see the problem that we as experience in worsening of FM as technological problem but rather the failure of human factor. I have no problems with the fact that FM is digitalized and that most of the “live” FM broadcast run off the BWF files.

http://www.ebu.ch/CMSimages/en/tec_doc_t3285_tcm6-10544.pdf

The problem is still people who do it as even the broadcasting of the row BWF allow a phenomenal quality if the people in the FM stations do not exercise their barbarianism.  There are two factors involved. Fists: no one edit live FM broadcast as there is not a lot of money in FM and the fact that the file are not intruded is huge. You can heard the instruments and people warm up as the performance progresses, you can hear normal reaction of musicians to own play – you can hear life as it unfolds without a “comfortably numb” sound. That comfortably numb of the “dead” sound is created by desire of sound engenders to improve something as there is no existing way to edit digital filers without activation DSP engine but use of DSP is a terminal death for digital recording. So, most of FM live broadcasts are row feeds. They append stat and end but they mostly don’t ”fix” the sound in file.  Second: the “sound quietly” of the people at the FM stations. This is huge as well. I have one of mine the most beloved local station WHRB - Harvard Radio Classical station and they have a phenomenal material and wonderful people working there. It is not very reach station with a lot of peoples contribute time and money voluntary sometime they run this programs fine with moderate compression and acceptable sound but sometimes, totally out of bleu, they the max out  compression au to the point that it exceeds all common sense. Now the question – why they do it? The answer - they do not care. In contrary I have another local classical station WGBH and this live broadcast have no problem with sound at all. Moreover the technician who works in there gave me his personal cell number and asked me to call him if I detect any compression in air during live broadcast. You see, it is not the equipment of technology but the people. BTW, in context of US emphasis compression does more damage to Sound then with European emphasis…

Yes, if everything comes together – the right people do the job and the recoding was proporly arranged then FM might throw outstanding results.  Here is what were hunting for… My hope is that my ideas of following:

http://www.romythecat.com/Forums/ShowPost.aspx?PostID=6917

http://www.romythecat.com/Forums/ShowPost.aspx?PostID=2949

...might materialize somehow. The digital Music Servers become more and more popular nowadays but the problem with those Music Servers is that the people who use them still forced to load in there the pre-caned music from the disks they were sold. They have no way to get fresh new files to this Music Servers. It is like using a reel-to- reel mashie – you can play a hundred tapes that you own and it is it. The existence and god FM is in my view is the only fresh window in the situation around the contemporary music distribution.

The Cat


"I wish I could score everything for horns." - Richard Wagner. "Our writing equipment takes part in the forming of our thoughts." - Friedrich Nietzsche
06-14-2010 Post does not mapped to Knowledge Tree
zanon
Posts 54
Joined on 11-14-2009

Post #: 4
Post ID: 13755
Reply to: 7673
I know these people
fiogf49gjkf0d
Romy:

I have worked at WHRB (and now outed myself) and I know these people.

They, like all college kids, have no understanding or awareness of broadcast quality at all. When they max out compression, and I do mean this, they may not even know they are doing it.

Why do you think DSP kills digital signal? Is it not already digital?
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   Target    Threads for related reading   Most recent post in related threads   Forum  Replies   Views   Started 
  »  New  Contributing factors in compressed sound..  Contributing factors of compressed sound....  Audio Discussions  Forum     3  32064  08-23-2007
  »  New  Attention Sound Engineers (compression and loudness)..  Injection channel and Romy's rules...  Playback Listening  Forum     48  221185  09-09-2007
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