Just about to order a few that4315 ICs to build a compressor pedal for my bass, wondering if anyone has experiance with these chips and if theres a better alternative. Thanks.
THAT Corporation 4315 Low-voltage Low-power Low-cost Analog Engine Dynamics Processor IC
THAT Corporation 4315 Low-voltage Low-power Low-cost Analog Engine Dynamics Processor IC
I had thought about using some of their stuff a few years back. Never got around to it. AFAIK That corp has all the best IP regarding VCA design going back decades. I'd think they are still in the forefront given everyone else is using DSP for just about anything they can.
Are you building one of their app note designs?
Are you building one of their app note designs?
Will start with one, not sure how much control I need. Would like to limit the number of pots on the pedal. Seen an interesting pedal design (Dark Glass?) that is a digitaly controlled vca. Lets them emulate many types of compressors. Way beyond me. But I am thinking of including a sidechain filter. Will experiment with that first.
I have found opto-coupler Vactrols to work well. NSL range from Silonex. Seemingly low tech, but deliver the goods. Built in hysteresis of the LDR simplifies control, matches music, and in a low noise circuit doesn't pump. Can be driven by an opamp rectification circuit. For bass/guitar you don't need threshold so it is one control. Gets thumbs up from bass player buddy. Current into the LED is easy to adjust, or driven by side chain. Implementation in neg feedback circuit, or simply as one half of volume pot.
LED drive is very consistent but LDR resistance varied by 40% in a lot of 10.
LED drive is very consistent but LDR resistance varied by 40% in a lot of 10.
My experience was similar. In my twenties I made a number of attempts to design and build guitar compressors. None of them were great, but the least unpleasant ones were always the LDR/LED (optical) ones. Apparently I couldn't screw those up too much even though I didn't have any test equipment except my ears, and didn't really know what I was doing. 🙂
All analogue compressors share the same problem as your car's cruise-control: they can't see what's coming until it gets here. So your car may shift up into 6th gear on a short level stretch of road, and then kick and struggle to downshift as quickly as possible to 3rd when you reach the steep hill just ahead and the car starts to slow down.
Analogue audio compessors have the same problem, because when the signal is small the compressor ramps up to full gain, and if an abrupt signal peak then arrives, the VCA struggles to lower the gain in time, the result usually being an audible "pop" before the VCA can clamp down on the suddenly-too-big signal.
This is where digital compressors have a huge advantage. They can run the incoming signal into a digital delay (a buffer), and "see" big signal peaks coming before they actually arrive, so that the digital equivalent of the VCA can react to them apparently instantaneously. This sort of look-ahead compression can avoid many of those nasty thumps and pops. (Just as a human driver with a manual-transmission car would see the hill up ahead, and shift down appropriately before the hill actually began to slow down the car.)
-Gnobuddy
Thanks for the replies. Of course digital compresion is great, but there have been many great analog compressors also. Most compression dosnt need instant attack, thats more limiting. Opto compressors are great for some stuff but too slow for others.
This seems like the logical starting point.
http://www.thatcorp.com/pedals/4316%20Battery-Powered%20One%20Knob%20Squeezer.pdf
What would you use the side chain for? I nice trick in mixing is to side chain the bass and duck it a bit when the kick drum hits.
I've used a fair few compressors over the years and, f I build another one it will probably be based on the Valve Wizard's Engineer's thumb, for all the reasons outlined in his article.
I still have a reel of THAT4301 laying around, which is the one incl a couple of opamps.
Really nice compressors btw if you wanna go for analog.
Really nice compressors btw if you wanna go for analog.
I have a Presonus Digimax which uses That4301. The mic preamps are good but limiting behavior is audible, and they know their stuff. I haven't investigated the implementation, but opto compressor seems free of artifacts by comparison.
Depends on the implementation. If limiting is audible you may be over driving it or it may be a lousey design. Optos are too slow sometimes, ecspecially for limiting. Even if its just for bass, different techniques (figers, pick, slap) may require dfferent attack/ decays. I like the extra control a VCA gives you.
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