Good DIY compressor for acoustic gee-tar?

Started by Ed G., November 20, 2003, 10:38:45 AM

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Ed G.

Looking for a good project to compress a Yamaha acoustic electric guitar. I understand comps are good for smoothing out that harsh piezo tone, but which compressors are the best? I was considering the LA-light, because I heard the optical type compressors don't 'squash' as much, but are there any other really good and relatively simple compressors? I will probably run the output of the compressor into the mixer board for performances.

Doug H

Ed, this isn't the "DIY answer"  :D but I use my Boss compressor with my yamaha acoustic/electric and it sounds great. I think the model # is CS-2, it's the blue one. I picked it up used for $40 a few years ago. I use a direct box into the PA and the compressor really helps when I switch from flat pick to finger picking, harmonics, staccato, etc... With the acoustic, it doesn't have noticeable distortion and sounds very clear.

Doug

Bill_F

I've been thinking about the same thing. Would the Q&D 2 at AMZ be a good compressor for acoustic? Does anybody have any experience with it?

Mark Hammer

The Q&D would be *very* good, since it also incorporates a low level expander in the same chip.  This pormits you to kill background noise when not playing.  You know those little rumblings that can quickly escalate into full-scale feedback?  The downward expander will allow you to effectively gate those out.

As a compressor, it works well.  Tons of gain.

hair force one

And if i want to build one for myself, which circuit shall i choose to tamper my elctro-acoustringy?

Bill_F

Thanks Mark for always being there with a good answer. You rock!

Bill

Ed G.

Quote from: Mark HammerThe Q&D would be *very* good, since it also incorporates a low level expander in the same chip.  This pormits you to kill background noise when not playing.  You know those little rumblings that can quickly escalate into full-scale feedback?  The downward expander will allow you to effectively gate those out.

As a compressor, it works well.  Tons of gain.

What about the SA571 compander chip? I've got an extra one of those, are there any projects out there that use this, or should I consult the app notes?

Mark Hammer

Sure, the 570/571 can also be put to good use.  There was a circuit in Polyphony way back when (Kind of redundant, eh?  They stopped being POLYPHONY in 1984.) by Thomas Figuerdo (I think that's how its spelled) called the "Penultimate Compressor".  The circuit/project used an NE572, but the basics of the design could easily be applied to a 570/571.  This gist of it is that it used band-splitting to process low and high end through their own half of the 572, with time constant set appropriately for each (via the rectifier cap to ground on pins 1 and 16).

Thee thing about compressors is that it is hard to find an attack/decay combination that works transparently across the entire frequency spectrum.  Even when you have variable control over these parameters, no matter where you set it to, it will be better for some frequencies than others.  This is but one of the reasons why high-end professional dbx and Dolby units (remember tape?) were always multi-band.  Splitting the signal into separate bands, each with their own signal level and compression needs, allows for a more transparent compression.  

I'm in no position to judge how many bands is optimal, but presumably 2 is better than 1, and 3 may hold some advantages over 2.  I would imagine it depends on the bandwidth of the signal you wish to compress.  And of course most acoustic guitars would have a pretty wide bandwidth, and some will have a big boomy bottom,crisp highs, and not a whole lot in between.  However many bands is ideal, the 570/571 provides the possibility for two bands on a single chip, inexpensively, and without a great deal of fuss.  In trading off complexity and cost against effectiveness, 2 is probably just fine.  If a person wants to go nuts on this, you can always incorporate a variable crossover frequency (the point where the upper and lower band are split), selectable time constant caps for each path, and variable band gain prior to compression to compensate for different band amplitudes at source.

If there is demand, I can scan and post it since T-Boy has fixed my site.  In the meantime, the short answer is Yes, and you should start looking at the various appnotes for the 570/571, either with the NE prefix or the SA prefix (same chip from our side).

Ed G.

Quote from: Mark HammerThis gist of it is that it used band-splitting to process low and high end through their own half of the 572, with time constant set appropriately for each (via the rectifier cap to ground on pins 1 and 16).

This sounds like a compressor stompbox put out by Trace Elliot about 10 or so years ago, it was a dual frequency compressor, with separate controls for low and high band compression.

Mark Hammer

Given that Trace Elliot has a history of providing amplification for acoustic instruments I'm not surprised.  Like I say, the wider the expected bandwidth of the input signal, the greater the likelihood it will benefit from use of multiple bands instead of applying a one-size-fits-all solution.