Quote:
Legal is 105% with stereo pilot. Occasional overshoots are not a problem. They were rare, as in 1-2 a minute. The 107% happened twice in 30+ minutes.
My meter hangs at 104-105% like it is glued there. I'm using an Inovonics 531 Modulation Analyzer.
I was unable to get the Trace Alpha card in a timely fashion, which seems to mirror other people's experience. And, although there is a modification given for the M-Audio card, I have not done that.
So the overshoot is 2% max with 1% more common. That would work for me. My Inovonics 530 is glued in place like it's seeing a test tone--truly amazing, and as noted, "tighter" than any commercial processor I've played with, yet it sounds more open. Amazing product.
Curious to know how the 104-105% figure was arrived at. FCC rule 73.1570 b (2) states that this applies only to SCA signals. Never have seen this interpreted as to allow modulation recovery of the stereo pilot. It is routinely applied to RDS signals however. The extra 0.5% per 1% was based on a 67khz and a 92khz subcarrier both operating at 10% (total of 20%), which allowed for an extra 10% total modulation. The goal was to encourage stations to implement SCA operation without fear of main channel loudness loss. The minimum sound difference the human ear can detect is 1db, which corresponds to the 10% loss using 2 SCA's.
(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 § 73.319 concurrently with the broadcasting of
stereophonic or monophonic programs may increase the peak modulation
deviation as follows:
(i)
The total peak modulation may be increased 0.5 percent for each 1.0
percent subcarrier injection modulation.
(ii) In no event may the modulation of the carrier exceed 110 percent
(82.5 kHz peak deviation).
The reference to 73.319 further confirms that the stereo pilot subcarrier is not included in this category by stating :
(a) The technical specifications in this Section apply to all
transmissions of FM multiplex subcarriers except those used for
stereophonic sound broadcasts under the provisions of § 73.322.
I'm not an FCC lawyer or anything remotely close but I've worked (and currently work) for large broadcast organizations that use every legal strategy to maximize modulation while staying 2-3% under the limit. I feel confident that if this were permitted, they would have been using it since the Report and Order that allows it was issued on April 9 1984.