Post by Boomer on May 5, 2017 21:55:48 GMT
There was some discussion about the uses for delayed audio at a radio station. I liked the fact that delay can be used in a station's dynamics processor to make the sound smoother, that's pretty clever!
In older and simpler circuits, a dynamics processor, like an auto level control, compressor, or limiter would react to level changes in real time as it was being fed audio, increasing the gain when it goes low, and decreasing gain when the sound is loud. In that way it follows the average level of the program from moment to moment, trying to keep the sound even and prevent transmitter over-modulation.
That can sound okay on a pop song that already has an even level, but add a sudden loud voice or 'hot' recording and that can overwhelm and fool the processing. It's like reaction time when driving, something blows in front of your car suddenly and you turn the wheel to avoid it, but might over-steer and find yourself in the ditch.
In dynamics control, a very loud sound might come through at full volume for part of a second, then the gain control will over react and cause a volume dip until it can recover and get back on the road at normal volume. I had a portable cassette deck as a younger pup that did just that, a burp right into the microphone would deaden the pickup for 3 seconds after, then the volume would come up aGAIN..
In radio studios, they couldn't allow that big intro peak, so they'd limit and clip off the peak so it wouldn't get to the recorder or transmitter and overload it. I hear it on radio station archives from the past, and TV promos, where the first syllables of a sentence are hard limited and raspy, clipped sounding, until the average level can come down, then the vocals sound pretty normal. In fact, I hear this on a lot of old recordings, usually local radio from the 1960s-'70s.
Now, things can sound a good deal better than that with better design of the gain control circuits, but you still have some kind of reaction time to deal with, since the gain control circuit doesn't know what's going to come next.
Enter delay. If you delay the audio slightly in a digital holding tank, the circuit can know what's coming and react to a peak by turning the level down before the audio gets played out of the delay. I assume the delay would also help to increase a level that suddenly dropped, as well. Wikipedia says:
en.wikipedia.org/wiki/Dynamic_range_compression#Look-ahead
Boomer
In older and simpler circuits, a dynamics processor, like an auto level control, compressor, or limiter would react to level changes in real time as it was being fed audio, increasing the gain when it goes low, and decreasing gain when the sound is loud. In that way it follows the average level of the program from moment to moment, trying to keep the sound even and prevent transmitter over-modulation.
That can sound okay on a pop song that already has an even level, but add a sudden loud voice or 'hot' recording and that can overwhelm and fool the processing. It's like reaction time when driving, something blows in front of your car suddenly and you turn the wheel to avoid it, but might over-steer and find yourself in the ditch.
In dynamics control, a very loud sound might come through at full volume for part of a second, then the gain control will over react and cause a volume dip until it can recover and get back on the road at normal volume. I had a portable cassette deck as a younger pup that did just that, a burp right into the microphone would deaden the pickup for 3 seconds after, then the volume would come up aGAIN..
In radio studios, they couldn't allow that big intro peak, so they'd limit and clip off the peak so it wouldn't get to the recorder or transmitter and overload it. I hear it on radio station archives from the past, and TV promos, where the first syllables of a sentence are hard limited and raspy, clipped sounding, until the average level can come down, then the vocals sound pretty normal. In fact, I hear this on a lot of old recordings, usually local radio from the 1960s-'70s.
Now, things can sound a good deal better than that with better design of the gain control circuits, but you still have some kind of reaction time to deal with, since the gain control circuit doesn't know what's going to come next.
Enter delay. If you delay the audio slightly in a digital holding tank, the circuit can know what's coming and react to a peak by turning the level down before the audio gets played out of the delay. I assume the delay would also help to increase a level that suddenly dropped, as well. Wikipedia says:
The look-ahead function is designed to overcome the
problem of being forced to compromise between slow attack rates that
produce smooth-sounding gain changes, and fast attack rates capable of
catching transients. Look-ahead is a misnomer in that the future is not
actually observed. Instead, the input signal is split, and one side is
delayed. The non-delayed signal is used to drive the compression of the
delayed signal, which then appears at the output. This way a
smooth-sounding slower attack rate can be used to catch transients. The
cost of this solution is that the signal is delayed."
problem of being forced to compromise between slow attack rates that
produce smooth-sounding gain changes, and fast attack rates capable of
catching transients. Look-ahead is a misnomer in that the future is not
actually observed. Instead, the input signal is split, and one side is
delayed. The non-delayed signal is used to drive the compression of the
delayed signal, which then appears at the output. This way a
smooth-sounding slower attack rate can be used to catch transients. The
cost of this solution is that the signal is delayed."
Boomer