Compressor build advice

[vacuumdust]

I'm looking to build a compressor and i'm leaning towards an orange squeezer.  I want it as a leave on sort of device to subtley even out my teles peaks and valleys.  Can someone direct me to a tried and true layout??  Also, if set for subtle compression, is the OS a quiet circuit?  If someone has a better idea for a compressor that does "subtle" better than the OS...I would love to hear about that too...I'm fairly green when it comes to comps.
THANKS!

[Mark Hammer]

Pragmatically, you'd be hard-pressed to find a better match to your current needs and circumstances than the OS.  It pretty much does what you want.  Though there are a few aspects of build/setup that some beginners find a wee bit tricky,, and though there are all sorts of other circuits, this one has been milked so much by so many that you will NEVER run out of solid troubleshooting or mod advice here.

Quiet?  There are two aspects to quiet, or maybe three.  I'll see when I'm finished writing.  First, there is the extent to which the circuit itself generates noise, and in this case there is not a whole lot the audio signal passes through between input and output jack, so not a whole lot of opportunity to acquire noise.  Even if you decided to spare no expense to use top-quality super-mojorific parts for least noise, that would only set you back a couple of dollars...it's that simple a circuit and signal path.  Second there is the extent to which the gain that is applied in the circuit (stock circuit has gain of x23) exaggerates whatever noise comes in through the input jack.  Feed it a quiet clean signal and it will behave much better; feed it a noisy fuzz and multiplying the residual hiss by x23 won't do anyone any favours, no matter how rare and exotic the op-amp is that you use. 

Third, and perhaps most interesting is the extent to which the circuit "breathes".  "Breathing" is a term that refers to the way a compressor "inhales" in an audible manner.  Keep in mind that the way a compressor works is to apply maximum amplification in the default no-input state, and then reduce amplification in proportion to the amplitude of the input signal.  Also remember that it applies this maximum amplification to whatever noise it sees at its input during the quiet passages too. 

When the "recovery" of gain - that is the restoration back to maximum gain/amplification - occurs, slower recovery will result in a stretched out transition to max.  If there is noise present on the input, then you will hear this in the output as a gradual increase in noise - "breathing".  If the recovery is fast enough, and the changeover from min gain to max gain quick, the slow "inhale" is not all that audible.  The crux of the matter is that in compressors the extent to which they introduce the illusion of sustain is a function of stretching out that transition or recovery time, so a lot of players like to have a slower recovery time/rate for that reason.  The price they pay is breathing.  If you set the recovery rate to be quick, you lose the audible breathing, but you forfeit the simulated sustain.  Happily, though, you get a more transparent-sounding limiting effect that appears to only keep the aberrant peaks in check.  Is faster always better?  No.  If the rectifier responds too quickly, it also pays too much attention to all the little micro-deviations in signal level and introduces audible "ripple" in the amount of amplification applied, which ends up being heard as a sort of distortion.

Why am I telling you this?  Because the OS has a fairly quick recovery rate, in large part due to the use of that 4u7 cap to ground and the 100k "bleed" resistor that lets the cap drain fairly quickly.  It's not TOO fast, though, and is much-cherished because it nicely balances off ripple and breathing in a simple and cost-effective form.

[vacuumdust]

Thank YOU!  Really...that was above and beyond.  I'm really impressed when someone takes the time to write something like that for someone they don't know.  Sounds like I'll be building the OS.

[snoof]

Some other builds that I have done that might meet your wishes are the "Flatline", and the "So Simple".  I like fairly subtle comps myself.  As usual, nice response Mark!

[Mark Hammer]

Hey, you deserve no less.

The micro-essay on "breathing" is the result of something that finally clicked in my own head the other day.  I figured I'd lay it out for you and for anyone else interested in the same subject matter.

The OS can also be tweaked to deliver prolonged recovery time, complete with breathing, but the stock design is intended to get in, do the job, and get the hell out of the way quickly.