High quality "soft" compressor/limiter

[jmar]

I know they are not something for the purist but frankly, I like a touch
of level control -- especially with the inconsistency of my digital wav files.

Can anyone point me to a project with a schematic at minimum for a simple HQ
compressor?

I remember seeing some circuits back in the late 70's and some that were built
around the signetics chips.

THANKS very much.

[pacificblue]

http://sound.westhost.com/project53.htm
http://sound.westhost.com/project57.htm

[fotios]

Originally Posted by pacificblue

http://sound.westhost.com/project53.htm
http://sound.westhost.com/project57.htm

The first circuit it is a simple limiter, and the second it is only a clipping indicator and nothing else.
jmar is asking for a compressor as i think, which is a more complex circuit. A limiter usually it detects a clipping that occurs in output and reacts by limiting the input signal in a preset level. It is like a servo-mechanism of instantaneous action.
A compressor it detects continuously any difference between input and output signals (except clipping, large phase shift, excesive slewing, short of output from very low loads etc) and it tries continuously to correct the error. It is like a servo-mechanism of continuous action.
I don't know what type circuits used today, but in the past the heart of compressors was an OTA (Operational Transconductance Amplifier) IC like the LM13700 of National or the CA3094 of Harris.
BTW a compressor it is not a High Quality circuit, because introduces big distortion in signals bellow 120HZ. I have seen with my scope this distortion in some P.A. amplifiers.

Fotios

[jmar]

Yeah, I know.

But I'm fed up with levels that are all over the place (partly my fault -- didn't normalize in some of my rips)

There are so many contradictions in audio -- and distortion or not, I do like a "touch" of compression -- less than 2 to 1 for sure.

Using a crappy Yamaha gc2020 right now but honestly, it HELPS what comes out of my usb audio dac.

I like it but it WILL get through to you after a while -- there is a definite listener fatigue factor.

Of course, the speakers love it !

[Nico Ras]

Go look here, it may be useful

http://mp3gain.sourceforge.net/

[andymac62]

have a look at
http://dt.prohosting.com/hacks/what.html
http://www.geocities.com/m_natsume/what_compressor.html
http://fileshare.eshop.bg/equipment_mfg/Urei_41.html

any of these would suit for hi fi & studio

[jmar]

Thanks Andy -- great stuff. I'm going to build that weak Joe.
5532's and a really a pretty clean signal path.

[sakis]

may i place a remark regarding project 53 from rod ???? ( led from the out will drive an LDR to limit the input )

it seems to me that this device will need a certain voltage in the output of the amp to activate the ldr ....well this may apply in amplifiers or setup that has a specific load 8/4ohms

cause if you use 8 ohms speakers and you need 10 volts for example to limit your input then this 10 volts in a 4ohm or 2ohm ( by mistake ) load will be way toolate fro your amplifier to limit ....