[Harp-L] Re: Using compression

[Richard Hunter <turtlehill@xxxxxxxxxxxxx>]

Gary Hodgson wrote:

>my digitech rp250 has Sustain, Tone/Attack, and Compressor Level.
>the Tone/Attack controls Tone if using digitech compressor, or Attack
>if emulating Boss CS-2.
>
>so my questions are:
>
>why do i want to use this?  what effect does it have on the sound,
>specifically harp sound.  i understand compression in general.
>
>how would you set those parameters for what type of effects?  would
>you set things differently in different circumstances?

Compressors reduce the volume for sounds that exceed a certain threshold (the "compressor level" in your case), according to the ratio of the compressor.  So if a signal exceeds the threshold by 6 DB, and the ratio is 3:1, the resulting volume increase will be 2 DB (meaning that for every 3 DB increase over the threshold, the final output increases by 1 DB).

In practice, this means that compressors smooth out the peaks in the sound, so you can raise the overall level.  

"Attack" refers to how long it takes from the beginning of the sound until the compressor starts to compress it.  A zero attack (which no compressor can actually achieve, because it takes time for a signal to go through any circuit) would mean that the signal is compressed from the instant it starts.  How fast you set the attack depends on how much of the initial accent you want to get through before the compressor clamps down on the signal.  "Sustain" probably means "release", which refers to the amount of time it takes for the compressor to let go of the signal once it diminishes below the threshold.  Sustain makes a lot of sense for a guitarist, not so much for a wind instrument like a harp, where you can basically sustain a note until the cows come home.  

I'd recommend that you start with a medium attack and release, and set the compressor level to a point where you can hear the difference.  Then raise the overall level to compensate for the reduction in volume that the compressor is imposing on the signal.  After that, you can decide whether you really like it. Remember that heavy compression with a fast attack is basically going to eliminate any accents from your playing.  For most of the music I play, that's not so good.  Also, keep in mind that part of the amp modeling you have in the Digitech is the "natural" compression that the amp itself imposes on a signal.  So if you're using the Bassman or Champ or Deluxe or other tube-amp models, you've already got some compression going on. You may not need more.

Most of my patches for the Digitech RP200 use pretty mild compression or none.  The exceptions are the patches that use effects like chorus or flanging, because you want the signal going into those effects to be pretty smooth, since the effect itself can get pretty peaky.  Actually, if I had my druthers, I'd run the compressor AFTER the chorus or flange.  But the RP200 doesn't give me the choice of where in the signal chain the compressor is placed--it's always first.

Hope this is useful.

Regards, 
Richard Hunter 
latest mp3s and harmoncia blog at http://myspace.com/richardhunterharp