COMPANDER ???

[Stephen]

Philips SA571N
--------------------------------------------------------------------------------

(compandor)


Can you build a simple compressor with one of these?  Would they be useful to buy some? Or are they only really in complicated Flangers and stuff??

[Mark Hammer]

That's a reasonable question to ask.

Companders using the 570/571 or 572 apply a complementary compression at the start of a noise-risky part of the circuit and expansion after the noise-risky portion.    This gets the signal safely through to the other side without much distortion or noise.  A bit like taking your shoes off and sneaking through with your stocking feet and your head tucked down so you don't get caught somewhere, then standing up straight and putting your shoes back on once you make it through.

You CAN build a compressor but the problem is that these chips are configured for a fixed amount of compression, to be counteracted by a fixed amount of expansion when the other half is set up for expansion.  If that's the "right" degree of compression for you, then you've got it made.  Otherwise, you may find it either too much or too little.

Craig Anderton designed a limiter for PAiA over 20 years ago that used one of these, and it wasn't half bad, although by today's standards it comes up a little short.  The fixed amount of compression was used to achieve varying amounts of limiting by having a variable threshold where the compression kicked in.

Normally, guitar compressors apply variable amounts of compression across the entire loudness spectrum.  In the case of this limiter, content below the threshold had NO compression applied.

[markm]

As always,
Very interesting Mark, thanks for shedding some light on this.
   MarkM

[Stephen]

Here is a schematic..I hope this is okay by Jack and the forum ...can you use this with these values and just use a minibooster on each side??  and not the IC chip?? Would that give a cool effect?? as you can see they alll come together and the values might work with a booster on each side for easiness.. thanks...apologize if this is not appropriate because of the copyright ..I copied it years ago...Thanks for any help...

[R.G.]

The NE570/571 and the SA570/571 are pin for pin compatible. The SA571 is still in production.

They can all be used to make a studio style compressor, compander, limiter, or a guitar style hard compression setup. It all depends on how you set up the chip.

The chip has an internal full wave rectifier, a multiplier/gain cell, and an opamp on board. The connections between the pieces are available on external pins, so you can set it up for soft compression/expansion, etc, but you can also set it up as a hard compressor.

There are (at least) two kinds of compressors - feed forward compressors and feed back compressors. In feed forward compressors, the envelope of the incoming signal is taken and that's used to set the variable gain, not looking at what is coming out the end of the thing. In feed back compressors, the envelope is taken at the end of the compressor and there is enough gain in the loop from envelope to gain cell input to force the output to be constant.

There are many apps for this thing explained in the "Compander Cookbook" application note from ... I think ST these days.

[Dave Eason]

aha, I had a headache with this chip and a wireless project, but it does work.  Although internal op amp is a 741, it is better to use external bifets like the 071 for better performance and low noise,

indeed, the compander cookbook is most useful:

http://www.onsemi.com/pub/Collateral/AND8160-D.PDF

In fact there are a few other useful documents, originally by Phillips semi:

http://www.semiconductors.philips.com/

and On semi:

http://www.onsemi.com

[Stephen]

Anybody show a basic scheme of a useable say compander.......cookbook like...so you could add it to a project very easily? Seems like all this chip can do why not use it in a booster or such for compression expansion companding etc.......What AGAIN if you used this circuit posted with a minibooster on both sides??  What would it sound like? S@#$.....I think this would be fun to play around with ANYBODY??

[R.G.]

Anybody show a basic scheme of a useable say compander.......cookbook like...so you could add it to a project very easily? Seems like all this chip can do why not use it in a booster or such for compression expansion companding etc.......What AGAIN if you used this circuit posted with a minibooster on both sides??  What would it sound like? S@#$.....I think this would be fun to play around with ANYBODY??

Sounds like that would be a great thing for you to do - eh?

[Stephen]

Well I know nothing of design....Yet I bought 4 chips and am going to see what this basic drawing can do .....Maybe a compander booster...

[R.G.]

Good boy! That's how you learn. Dig in!

[markm]

Well I know nothing of design....Yet I bought 4 chips and am going to see what this basic drawing can do .....Maybe a compander booster...

You're braver than I
"May the Force be with you"

[Dave Eason]

companders are often used with old "bucket brigade" IC's, ADC's/DAC's (CODECS essentially) and radio systems because all three posses relatively narrow dynamic range transmission mediums, so the compander is just used to reduce the dynamics of the audio signal during "transmission".  Of course it could be used for anything else, especially adaptive processes where the input RMS or avergae is measured and used to alter the gain of the system.

[Stephen]

 I think common knowledge is right with the compander being used like you say..Look at the easyness of adding this to a circuit? I dont know what it can do, but an expander is pretty cool!   Now for the compressor part it would limit the waveform but you alter it after the compression.. I think you want to have a little boost in front of the chip to drive compression or expansion!! I am kind of wondering what the real dynamics to a booster circuit with fets would sound like?? Might sound like  ^%$#  ...I dont know!!!

[Stephen]

I have the board built like in the scheme with a fet booster.. gain pot.. in the front.... and a mini-booster volume pot.. after....Need to wait for the chip now!!  Man there is a lot of electros in there, but easy enough!!! I sort of cant wait to see what the chip will do ....I tested the circuit with jumpers and a dvom meter it is ready.....Might be like the TECH 21 comptortion maybe??? With the switch for expansion!!!

[Stephen]

IT WORKS used the scheme from the comprexx fuzz and did the j-fet booster in front with a pot and than a minibooster after the compander....The expansion is quiet with a little brightness very clean with no sustain.. stops right away!! Thw compression is a different animal whewwwww...it sings,  noisy too..has a nice singing drive to it and with the switch to expansion you can go to a cleaner quiet sound ...Oh well need to put it in a box ..NO switch squel which drives me nuts with fets!!! 

[Jaicen_solo]

Am I correct in thinking that if I took the output of the compressor (of the 570), fed it into a fuzz circuit and then into an expander, I could get a more dynamic type of fuzz effect, as in the EHX Graphic Fuzz?? It's something i've been thinking about for some time, but never really done anything about.
Is it possible to set the amount of decay on the expander or is it directly related to the input envelope?

[Ben N]

Am I correct in thinking that if I took the output of the compressor (of the 570), fed it into a fuzz circuit and then into an expander, I could get a more dynamic type of fuzz effect, as in the EHX Graphic Fuzz?? It's something i've been thinking about for some time, but never really done anything about.
Is it possible to set the amount of decay on the expander or is it directly related to the input envelope?

Its been done--what was the name of that magazine article project?   Mark, is that part of your online stash?

Ben

[Stephen]

I would really like to see some draw ups of how to use this chip...This is the only thing I have. The compressor is strong and a little noisy but not in a box yet. The expander is very quiet and almost needs some gain to it.. i wonder if I let both go through together what it would sound like...I used this scheme from the infamous Jack AMZ...thanks !!!!  ...It works and is useable but maybe someone else has done more work with this chip?? I like the sound a little punchy on the low strings not as clear as you would maybe like ...kind of punch and than the note.......Is this a compressor needing adjusting.....The expander kind of punchs things sings too!!  I have three more chips to play with what to do now?

[Stephen]

Does anybody know more on how to use this chip........ thanks

[A.S.P.]

it`s all in the app-notes!

(the commercial pedals and the cloners just keep copying from each other since 30 years - nothing new from there...)