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Re: [ARSCLIST] Loudness, was Libraries disposing of records
Thanks for reprinting this for everyone.
It should be noted that exceeding the limits unintentionally produces
all sorts of problems on the transmission and/or interference with other
stations. Many receivers, particularly FM, have difficulties when
presented with excessive FM deviation from a transmission. For those
unfamiliar, deviation in FM is basically the bandwidth the signal
occupies. Excessive deviation by overmodulation means the station's
signal can expand in frequency enough to 'step on' the signal from
another station, among other things. The references to modulation over
100% may confuse some unfamiliar with the ins and outs of RF.... I can
see some folks wondering how you can actually have modulation exceeding
100% while still being technically undistorted.
In AM transmission (amplitude modulation), 100% negative modulation
roughly means no output from the station at all, while 125% positive
modulation means the transmitter is being driven to a power level likely
outside the FCC license permission for that station. The coverage area
for any station is meant to never overlap that of another station on the
same frequency at a different location. Excess power used for any reason
is not allowed because of that. At he risk of going in the weeds
slightly, let me mention that this is also the reason stations may well
have a different licensed power for the daytime vs. the night time....
For TV, the audio is sitting right next to the video signal, and
excessive deviation will really cause a problem there if the two signals
collide...
Note the last item listed below:
(c) If a limiting or compression amplifier is employed to maintain
modulation levels, precaution must be taken so as not to substantially
alter the dynamic characteristics of programs.
This has always been impossible to enforce, as subjective as it is, and
so the perceived need for stations to be as loud or louder as you tune
across the dial looking for your favorite music. Sad, really...
-----Original Message-----
From: Association for Recorded Sound Discussion List
[mailto:ARSCLIST@xxxxxxx] On Behalf Of Parker Dinkins
Sent: Sunday, January 07, 2007 7:54 AM
To: ARSCLIST@xxxxxxxxxxxxxxxx
Subject: Re: [ARSCLIST] Loudness, was Libraries disposing of records
on 1/6/07 9:24 PM US/Central, Scott Phillips at
scottp@xxxxxxxxxxxxxxxxxxx
wrote:
> I have been in the recording industry in one way or another for years,
> but I also possess an FCC license that started out as a first class
> license for radio, when they were 'hard to get'. Put bluntly, there
> are legal restrictions that AM/FM broadcasters need to adhere to, and
> they limit such things as dynamic range. They MUST have gear that
> restrains/maintains things in those areas. They are NOT going away,
> they can't. With that in mind, at the very least record
> companies/producers/engineers/mastering engineers should understand
> this. Radio CAN'T change this, it is the law. Sure, they have some
> latitude as to how the gear is adjusted, but less than you might
> imagine. Once it seemed like this was just common recording
> engineering knowledge, I must be getting old...
>
> As a result, they have to be pretty inflexible as to their processing.
> Sure, they also want to be the loudest station as you tune across the
> dial in most cases... But that WILL happen, HAS happened for more
> years than I've been alive. Still, they have more restrictions
> actually placed on them that the rest of the recording chain. This was
> not true when vinyl was king, it was different but 'similar' in
> discipline. If the industry was in fact recording and mastering to fit
> the needs of radio, it wouldn't sound like it does right now.
See (US only, of course)
FCC Rule [portions omitted for clarity]
73.1570 Modulation levels: AM, FM, and TV aural.
(a) The percentage of modulation is to be maintained at as high a level
as is consistent with good quality of transmission and good broadcast
service, with maximum levels not to exceed the values specified in
paragraph (b). Generally, the modulation should not be less than 85% on
peaks of frequent recurrence, but where lower modulation levels may be
required to avoid objectionable loudness or to maintain the dynamic
range of the program material, the degree of modulation may be reduced
to whatever level is necessary for this purpose, even though under such
circumstances, the level may be substantially less than that which
produces peaks of frequent recurrence at a level of 85%.
(b) Maximum modulation levels must meet the following limitations:
(1) AM stations. In no case shall the amplitude modulation of the
carrier wave exceed 100% on negative peaks of frequent recurrence, or
125% on positive peaks at any time.
(i) AM stations transmitting stereophonic programs not exceed the AM
maximum stereophonic transmission signal modulation specifications of
stereophonic system in use.
(ii) [omitted for clarity]
(2) FM stations. The total modulation must not exceed 100 percent on
peaks of frequent reoccurrence referenced to 75 kHz deviation. However,
stations providing subsidiary communications services using subcarriers
under provisions of Sec. 73.319 concurrently with the broadcasting of
stereophonic or monophonic programs may increase the peak modulation
deviation as
follows:
(i) [omitted for clarity]
(ii) In no event may the modulation of the carrier exceed 110 percent
(82.5 kHz peak deviation).
(3) TV station. In no case shall the total modulation of the aural
carrier exceed 100% on peaks of frequent recurrence, unless some other
peak modulation level is specified in an instrument of authorization.
For monophonic transmissions, 100% modulation is defined as
<plus-minus>25 kHz.
(c) If a limiting or compression amplifier is employed to maintain
modulation levels, precaution must be taken so as not to substantially
alter the dynamic characteristics of programs.
--
Parker Dinkins
MasterDigital Corporation
Audio Restoration + CD Mastering
http://masterdigital.com