Instantaneous (analogue) compression of speech signals

Does anyone here have any experience of instantaneous (analogue) compression (aka soft clipping) of speech signals? I've been doing a little work on it but I'm unable to judge the resulting sound quality. Why do treble boost controls no longer have any audible effect for me? (;-)

As in, "run it thru a tooob" ;-)

...Jim Thompson

-- | James E.Thompson, P.E. | mens | | Analog Innovations, Inc. | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | Phoenix, Arizona Voice:(480)460-2350 | | | E-mail Address at Website Fax:(480)460-2142 | Brass Rat | |

What the hell is "soft clipping?" It sounds like "golden ears" audiophile mumbo-jumbo.

Hey, the bright side is you don't have to spend any money on components to boost the bright side.

I read in sci.electronics.design that Rich Grise wrote (in ) about 'Instantaneous (analogue) compression of speech signals', on Mon, 3 Jan

You have determined the problem, but the cause is idiopathic and familial. My misspent youth dates from just after Greensleeves was top- of-the-pops. (;-)

I read in sci.electronics.design that Adrian Jansen wrote (in ) about 'Instantaneous (analogue) compression of speech signals', on Tue, 4 Jan 2005:

Yes, and low-cost. FFT and DSP solutions are unlikely to be justifiable on a cost/benefit basis, but a couple of diodes and a quad op-amp is a different matter.

Indeed.

No, it's quite legitimate. You know what hard clipping is; flat tops on the sine waves. Soft clipping gives rounded tops; in principle produced by:

o----R------+----+-----o | _|_ _V_ / In | | Out R' R' | | o-----------+----+-----o

As a start, at the very least, don't you need to define the level at which ONSET of amplitude reduction begins, and then an absolute MAXIMUM output level?

...Jim Thompson

Back in the ancient days of 27MHz CB radios there was heaps of work done on compression and clipping to get the most "voice power" onto the carrier. Is that the sort of compression you want ?

Your ears, like mine, probably date from this period too, if you cant hear treble anymore :-)

I read in sci.electronics.design that Anthony C Smith wrote (in ) about 'Instantaneous (analogue) compression of speech signals', on Tue, 4 Jan 2005:

Thanks for that. Are you sure it's even harmonics? If the clipping is precisely symmetrical the harmonics are all odd order.

Anything using a rectifier involves a time constant, and I want to avoid that because it introduces an extra variable - the time constant.

How about "compandors" used by most radio stations to keep their modulation index maxed out....

...Jim Thompson

Hi John, have a look at alesis semiconductor/aka wavefront semi available from profusion. They do a very cheep DSP, AL3101 IIRC, less than a fiver, that is designed for this sort of thing. There is a Perl based complier for it somewhere as well, freeware

martin

Serious error. All shortcuts have disappeared. Screen. Mind. Both are blank.

Poor Reg, a senile ending to a once-creative mind :-(

...Jim Thompson

-- | James E.Thompson, P.E. | mens | | Analog Innovations, Inc. | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | Phoenix, Arizona Voice:(480)460-2350 | | | E-mail Address at Website Fax:(480)460-2142 | Brass Rat | |

In message , John Woodgate writes

Howzabout a potential divider with the top leg being a small incandescent lamp. Also acts as an emergency beacon where the louder you call for help, the brighter is the lamp.

Wayne Bridges is the expert with this method of course.

Cheers

I thought you were the audio expert ?:-)

What curve would you like and I'll create it in circuitry for you?

...Jim Thompson

Not too too badly. TI's MSP430 line pulls less than 2mA and doesn't need an external clock. I haven't read up specifically on any of the EMC issues, but with no loops or high currents it's hard to see what would broadcast.

I read in sci.electronics.design that Keith Wootten wrote (in ) about 'Instantaneous (analogue) compression of speech signals', on Tue, 4 Jan

Interesting, because it has potentially less distortion than diode clipping. It's not quite 'instantaneous', though, and it's not so easy to find suitable lamps.

Does he have a web site?

I didn't note a fee attached to my offer ;-)

OK. I appreciate how hearing loss slips up on you. I've very little high frequency response in my left ear... If I bury my right ear in the pillow I don't even hear the phone ring in our bedroom (high-pitched electronic "ringer").

...Jim Thompson

Good point now i look at it- I used this method with a pair of 3v3 zeners in parallel with a 10K feedback resistor on a TL072 (2k2 Rin) and the even harmonics increased IIRC when viewed with FFT analyser on my AP- still the ears test is the best and it sounds OK when used on a mic preamp- limiting starts around 2.6V and still has round corners when you hit the limit at 4V (peak) ie no sharp transistion from the rising of the sine wave and the clip point line. simplest is to try it and see- its simple enough- regards Anthony