Why use your limiters? the bigger nice looking 19 inch rack limiters from Behringer and other similar brands are the same price?
For FM broadcasting the attack has to be very fast at all audio frequencies, audio above 15KHz should be cut and pre-emphasis has to be applied before limiting.The commercial 19 inch rack mount type limiters, compressors and audio processors that are for bands, discos and recording studios don’t do this.
Our limiters do not use any digital sampling, they are high quality, low distortion, low noise and analogue design, perfect for FM transmitters.
Our limiters start to cut off sharply at around 14 KHz using a Salem and Key active filter. The commercial 19 inch rack mount type work up to 20KHz and way beyond, in the applications they are designed for this is okay and there’s no reason to cut the frequency above 15 KHz. They are not designed for FM transmitters
Our limiters apply the pre-emphasis before limiting. The 50uS and 75uS FM pre-emphasis works on the condition that the high frequencies start to roll off at about about 6dB / octave at around 3 KHz in most music. However occasionally the music or audio may be exceptional and high frequency energy above 3 KHz may be excessive. In the case of this, the limiter needs to attack and attenuate these frequencies fast, on the rise of one cycle. The 19 inch commercial rack mount type do not have any facility to apply the pre-emphasis before limiting. This means the pre-emphasis is applied after limiting and processing this causes excessive FM deviation at all audio frequencies above 3 KHz.
In a 19 inch commercial rack mount type limiter there is no cut to the frequencies above 15 KHz and the pre-emphasis is applied after limiting, this causes:
The 200 KHz channel bandwidth to be exceeded and the audio bleeds over into the channel above and below. This causes unpleasant interference to the radio stations in these channels and violates the maximum bandwidth permitted by the authorities in all countries of the world. (ITU-R BS.450-3 (11/01) FM Broadcasting at VHF)
The stereo ultrasonic side-bands in the MPX composite signal between 23 and 53 KHz and the RDS/SCA at 57 KHz to be interfered with. This causes coarse distortion to the stereo audio and loss of RDS/SCA. This will be severe with low quality computer sound cards and other equipment that uses digital sampling such as a mixers, players, processors etc.