Questions on Attack and Release Controls

[Astronaurt]

Hey folks, I've been working on a new design for a Noise gate that preferably doesn't suck and one of my requirements for that is for it to have full range and useful Attack and Release controls. The problem is, I only have an extremely vague idea of how to achieve this electrically. Specifically how can you even get into the realm of a 300ms-500ms attack or release time without using a Clock chip or comically oversized caps/inductors? I've been searching the forums for something along these lines with no luck. Anyone got some schematics showin' how they'd do it? I really want to know the meat and potatoes of how Attack and Release controls work.

at the moment, my design is using a full wave rectifier/buffer to drive a FET into opening or closing it's gate, with an LED turning on and off in accordance. The LED's opto-isolated to an LDR which forms the bottom half of a Voltage divider to ground. Playing above the threshold closes the FET gate, turning off the LED, causes the LDR to return to meg-ohms of resistance, so that the signal is not attenuated going into an output buffer, Etc. etc. I'm not sure WHAT configuration of Attack and Release controls I want to put into it, or where in the detector path they would even go. I'll try and Mock up a schematic to post soon, but in the mean time does anyone have any thoughts?

[Mark Hammer]

When you see longer-than-sniffle Attack times, the rectifier output is generally buffered with a high input impedance op-amp.

[merlinb]

Noise gates normally have only an on/off action- why would you want an attack/release function? It's not a compressor! I could just about see why you *might* find a release function useful, but not an attack function.
Anyway, assuming you are rectifying the audio with a diode feeding a big capacitor, to generate the control voltage, then whatever resistor you put in parallle with the cap will control its release (discharge). You could control attack with a resistor in series with the diode, to slow down the charge time.

[nexekho]

I was thinking of designing a custom noise gate too.  Basically the same set of ideas, not looked into it.

[artifus]

Noise gates normally have only an on/off action- why would you want an attack/release function? It's not a compressor! I could just about see why you *might* find a release function useful, but not an attack function.

have to disagree with you there. both functions are very useful and often essential in a noise gate.

[nexekho]

Noise gates normally have only an on/off action- why would you want an attack/release function? It's not a compressor! I could just about see why you *might* find a release function useful, but not an attack function.

have to disagree with you there. both functions are very useful and often essential in a noise gate.

Agreed.  Being able to adjust the settings to match your setup is more helpful than locking them away and I imagine with enough settings sweep you could get a nice swell.

[Astronaurt]

I guess you could say what I'm working on is more of an Expander than a clear cut gate. The very reason I normally don't like Noise gates is because of the Choppiness you get with the ends of notes, especially if you WANT to put it after a noisy, high-gain pedal. I'm thinking attack and Release controls would allow you to compensate for this, and maybe add in their own musical effect. The other day I was watching a video of Alan Parsons in the studio basically turning an acoustic Piano recording into what sounded like a Synth pad, by exaggerating the attack time on the Noise gate/expander he was using. Kind of a Slow Gear style effect, it was cool stuff.

But @Merlin, that makes enough sense; What sorts of values would you use for the release control in parallel with the Capacitor? Say I have a 1000uF cap, what makes sense, a 100k pot, 500k, 1M? I'm afraid I don't know what the Formula would be to figure that out. I really appreciate the input by the way, I'm a huge fan of your books! 

[Mark Hammer]

Make a PAiA Gator: http://www.paia.com/talk/viewtopic.php?f=6&t=204

The Gator does what you describe.  It is a noise gate with the capacity for slow gate-on time, producing a volume swell.  I made one, and it works fine.  The stock circuit uses a form of effect cancellation that you may prefer to replace with a true bypass, particularly since in effect-off mode, the signal passes through a 3080 - not the best insurance of a robust clean signal.

[Rodgre]

I second the suggestion of the Paia Gator but you'll have to find a way to alter the release. There is no provision to adjust it as is. In fact, if I recall correctly, it shuts the gate down by actually killing power to the gain control IC (a 3080?). There's no polite way to get a smooth and adjust the decay in that scenario.

[PRR]

> Noise gates normally have only an on/off action- why would you want an attack/release function?

Good ones always have action-time networks.

Definitions are different.

"Attack" ignores a short spurt of noise (line clicks, mike bump) and triggers ON only if the racket continues.

"Release" holds the gate ON for some time after the sound has "decayed". The threshold is often set high (to further reduce false triggering), higher than speech sibilants or note fade-outs. A several-second hold-ON delay allows soft parts following loud parts to pass through.

> how can you even get into the realm of a 300ms-500ms attack or release time

Study R-C network theory. A 1uFd cap drained by a 1Meg resistor will hold 37% of initial charge for a whole second. As Mark says, such large resistances often need buffers.

The general idea:


> drive a FET into opening or closing it's gate, with an LED turning on and off in accordance. The LED's opto-isolated to an LDR which forms the bottom half of a Voltage divider to ground. Playing above the threshold closes the FET gate, turning off the LED, causes the LDR to return to meg-ohms of resistance

I have _NO_ idea what your scheme is, or why it needs both an FET and an LDR. In any case, anything using an LDR will not be able to do "fast". This may be less important in a noise gate; still it is a classic problem that a word/note with a sharp initial transient comes out "blunted", the first transient missing.

[Mark Hammer]

I second the suggestion of the Paia Gator but you'll have to find a way to alter the release. There is no provision to adjust it as is. In fact, if I recall correctly, it shuts the gate down by actually killing power to the gain control IC (a 3080?). There's no polite way to get a smooth and adjust the decay in that scenario.

I suspect that could be done by means of a variable resistor to ground in parallel with the 10uf cap labelled C8.