automatic compressors

I was thinking the other day How hard would it be to build an analog compressor that is automatic. Ideally would have no control's at all. No input pots, No output pts, No ratio control, no attack time or release time No make up gain Knob. Just a box with connections. Essentially It would compress as much as needed based on input levels much like an opto compressor But have automatic makeup gain. No need to set up just plug and play. My current brain fart is wondering if such a device exists.

well, there are those dbx compressors with just a "compression" slide pot on them.

'over easy' gets pretty close, surely?

yes DBX is close but not exact. I am talking no controls of any kind. Just A box that based on input signal level would compress and adjust all controls automatly. It would only have connectors. Perfect for artists and producers who think to much.

There were some points about "auto" behaviour in "What?" compressor article page. Some really simple ideas I have seen on one old Elektor circuit description, but how to make an analog circuit "idiot user proof at all settings" that is a question...

I am talking no controls of any kind

Click to expand...

Very FWIW:
The idea of this thread is nice and way more nicer than my sad & obvious reply :wink: : how's the box to know how much you want to compress ? Attack & release-times could indeed be done auto in some way, but such a thing as compression &/or threshold... It's of course easy to keep those pots inside and set them 'acceptable'.

It makes me think a bit of 'I want a box that just plays music'. So you put a random CD in it and tape & hide the CD-loader mechanism. Will it be usable for too many others ?

www.thatcorp.com have the one knob squeezer somewhere in their application notes...still one knob too many? :wink:

Bjorn

if you are not a FM transmittter and dont have enough of an idea about how to use a limiter, consider not using one. Its really ok to not use a limiter. Spreading the gospel on that is probably a better use of time than designing a box with no knobs.

I should probably keep opinions to myself on this board like this as there are probably some appropriate places to use a no frills box but trying hard to spread the good word....

The auto release setting on a compex is pretty awesome, actually its downright amazing for buss limiting. If you can cobble designs together, using the auto release from the compex circuit would IMO be a step towards a box that is usable vs. a box that is just simple.

dave

> Essentially It would compress as much as needed

"As much as needed" for WHAT???

I have an organ recording with a couple dB taken off a few note-starts.

I have some rock that has been squashed like a pumpkin under a steam roller.

If I used the rock-smash compression on a string quartet, the loud parts would be un-loud, making the background noise seem large.

You need a knob to say "trim the stray hairs" or "mash it flat".

I guess what you are thinking of is the ALC in $13 cassette recorders, and the slightly better ALC in DiskMan recorders, and camcorders. I've occasionally been amazed at how "OK" a no-knob ALC can be, but I've also been disgusted when a fine dynamic concert plays back (and sounds) like the meters are stuck. Delicate piano tinkle, big trumpet blare, all the same loudness.

How about a compress with just one knob?

I like the "Compression" knob idea. Make it adjust the threshold and makeup gain proportional to each other, so the signal is the same level going in, as it is going out yet compressed.

Increasing the threshold would also increase the makeup gain to compensate... and vice versa.

check out: http://www.silonex.com/audiohm/compressor.html

I´m looking an Elektor 964065-11 circuit, on "extra" pages of 306 circuits-book. Looks like an automatic volume control or limiter with quick set and very slow release, signal adjusting done with cmos 4066 analog swithches.

But signal path is analog. Are digital chips alowed?

Focusrite's Platinum Penta has an opto compressor which can be set without touching a knob... you do have to tell it what the source material is though, so it can go to a preset the engineers think is suitable. I used one for a while and thought it sound OK in most cases. It was always just slightly "wrong" or different from the kind of sound I would have chosen though.

I think this kind of thing ruins the whole idea of compression in the first place. If you just want a mindless level control then go with AGC.... either something fast and pumpy or slow but with a limiting stage. Compression is all about tinkering with punchiness and dynamics... and that depends not only on what the source material is, but how the specific instrument sounds and how it was mic'd etc... not to mention what final sound you are looking for!
If you don't know exactly how to work the tool you will probably end up with something that just sounds wrong like the Penta did. It worked but was always unnatural. And even the most advanced DSP isn't going to be able to either read your mind or know exactly what to do with a signal in order for it to sound best...

You know what should be invented... the anticompressor. A small, easily attachable mod for existing compressors.

What it does is, once the engineer has set the threshold and is happy with the level of compression, the "anticompressor" automatically rolls the threshold back 2 or 3 dB without the engineers awareness. :wink: :roll:

[quote author="pucho812"]yes DBX is close but not exact. I am talking no controls of any kind. Just A box that based on input signal level would compress and adjust all controls automatly. It would only have connectors. Perfect for artists and producers who think to much.[/quote]

this would be very useful on a console....just push a button for a compressor to be in..... now that would be ultra cool.... very marketable.

is there any info out there on how the human ear responds to loud sounds? When I listen to some really loud (live) drums up close, they SOUND compressed :grin:

I understood this is also (one of the) thought(s) behind compressing them: compress them and you get the ('false') impression they're loud.

.just push a button for a compressor to be in

Click to expand...

Now your talking. :thumb:
( may possible have live board aplications only?)

I am thinking it would have to be an opto comp.
I am thinking That based on input level signal. It will auto adujust threshold. Then based on threshold level it will scan and attinuate the make up gain. I really like the idea of an insert switch and thats it. If anything the idea of this comes about with a producer I worked with who loved to be over hands on and in some cases would prevent me from doing my Job. If I inserted an EQ and made adjustments it was good but if he made the same adjusments it was godlike. Plus he loved to move knobs after I was done and not really do anything just to say "Did you see how I set to comp just right?" So for people like him it has no controls and just compresses based on input level. Compressor in button only