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previous: jon HiAnyone ever build one? I'... -- 5/9/2000 1:40 PM

Re: Building an Attack Delay

5/9/2000 2:20 PM
Mark Hammer	Re: Building an Attack Delay Attack delays are essentially sluggish noise gates. Noise gates work by attenuating the signal unless it detects signal over a threshold value (presumably higher than the background noise it is trying to suppress). Once detected, the audio "gate" opens up and allows the signal to pass until it decays below the threshold value again. Most decent noise gates will include controls for gate attack and decay time so that the signal can be made to sound more natural (fading out naturally, and having a less abrupt and switch-like onset). Attack delays exaggerate the attack time so that the gate turns on very gradually. The inexpensive "Gator" kit from PAiA (www.paia.com), as designed by Craig Anderton, is essentially his noise gate project from the EPFM2 book, retweaked to provide the option for very slow gate turn-on time. The key element to the Slow Gear is the FET that is used to attenuate, and fade in the guitar signal to the output. Another approach is taken with analog guitar synths. Here, there is a generic "event detector" module, for identifying new notes. This will result in a trigger/gate pulse being sent to an envelope/function generator. This latter module then generates a fixed envelope voltage (the old ADSR type or simply an AD type), which can be used to control lots of stuff. If you use it to control a voltage-controlled amplifier (VCA), it can automatically vary the volume of whatever you feed the VCA to produce slow onset sounds or whatever you set the envelope generator controls for. This is obviously more complicated. One important thing to keep in mind about both systems is that they work by identifying "new events", without discriminating between strings, and generally without discriminating between notes that came from out of silence and notes that were added on top after the first note had been plucked. This is the complicated way of saying that such an effect works best when you play monophonically (single notes) and leave a bit of space between notes. You CAN play chords on them without chaos (unlike octave-down boxes), but the chord has to feel like a single note to the unit to make it behave right. Incidentally, more effective simulation of "backwards tape" tone will generally involve some timbral adjustment too. Normally, the initial attack of a note contains more harmonics, so a decent emulation of reverse tape would include some envelope-controlled filtering as well. You could do this within the design of the effect, or simply tack on an envelope controlled filter afterwards, set for minimal to modest modulation.

5/9/2000 2:20 PM

Mark Hammer

Re: Building an Attack Delay

Attack delays are essentially sluggish noise gates. Noise gates work by attenuating the signal unless it detects signal over a threshold value (presumably higher than the background noise it is trying to suppress). Once detected, the audio "gate" opens up and allows the signal to pass until it decays below the threshold value again. Most decent noise gates will include controls for gate attack and decay time so that the signal can be made to sound more natural (fading out naturally, and having a less abrupt and switch-like onset). Attack delays exaggerate the attack time so that the gate turns on very gradually. The inexpensive "Gator" kit from PAiA (www.paia.com), as designed by Craig Anderton, is essentially his noise gate project from the EPFM2 book, retweaked to provide the option for very slow gate turn-on time. The key element to the Slow Gear is the FET that is used to attenuate, and fade in the guitar signal to the output.

Another approach is taken with analog guitar synths. Here, there is a generic "event detector" module, for identifying new notes. This will result in a trigger/gate pulse being sent to an envelope/function generator. This latter module then generates a fixed envelope voltage (the old ADSR type or simply an AD type), which can be used to control lots of stuff. If you use it to control a voltage-controlled amplifier (VCA), it can automatically vary the volume of whatever you feed the VCA to produce slow onset sounds or whatever you set the envelope generator controls for. This is obviously more complicated.

One important thing to keep in mind about both systems is that they work by identifying "new events", without discriminating between strings, and generally without discriminating between notes that came from out of silence and notes that were added on top after the first note had been plucked. This is the complicated way of saying that such an effect works best when you play monophonically (single notes) and leave a bit of space between notes. You CAN play chords on them without chaos (unlike octave-down boxes), but the chord has to *feel* like a single note to the unit to make it behave right.

Incidentally, more effective simulation of "backwards tape" tone will generally involve some timbral adjustment too. Normally, the initial attack of a note contains more harmonics, so a decent emulation of reverse tape would include some envelope-controlled filtering as well. You could do this within the design of the effect, or simply tack on an envelope controlled filter afterwards, set for minimal to modest modulation.

Replies:

Mark Hammer Interesting followup -- 5/9/2000 4:26 PM