Re: "all pass" thought about (analogue) compression

From: Ban (bansuri_at_web.de)
Date: 01/07/05 

Date: Fri, 07 Jan 2005 06:41:39 GMT

Ken Smith wrote:
> If you take a sine wave and run it through a circuit that does:
>
>
> Y = X ^(17/19)
>
> the sine wave's RMS amplitude will be compressed towards about 0.98V
> RMS and there will be some distortion. The 3rd harmonic will be
> about 2.7%.
>

Absurd, I think you should look how a sine wave changes its values, it gets
zero, then negative, try it then. How do you want to compress, analog or
digital? and how do you want to get the envelop signal. Which time
constants?

> Assume that the sine wave we start with is 300Hz.
>
> A phase shifter (all pass filter) can be made with a Q such that the
> 900Hz, 3rd harmonic is shifted by 180 degree relative to the 300Hz
> sinewave.
>
> If we take this shifted signal and do another X^(17/19) operation on
> it, the 3rd harmonic will only be about 0.2%
>
> You don't need the phase shift to be exactly 180 degrees. Any
> non-zero phase shift and two steps of (17/19) soft clipping will
> result in less harmonic content than one step of (17/19)^2 clipping
> would produce.
>
> If more distortion can be lived with, a lower power such as (11/13)
> could be used.
>
> Since the band of interest is 300Hz to 3KHz, we don't have to worry
> about the harmonics of the frequencies above 1KHz. Those can be
> removed with a simple low pass filter. I haven't verified it yet but
> it seems to me that 3 stages of phase shifter and 4 clippers should
> be able to make a significant compression of amplitude but make less
> that 5% distortion on a sine wave.
>
> The intermodulation distortion will not be made zero by this method.
> If the input has more than one frequency component, the distortion
> will be much higher.

Tell me which drugs are you using? Better use a u-law A/D or something
analog like THAT4301(better than 0.1%). 

-- 
ciao Ban
Bordighera, Italy

Relevant Pages

  • Re: HP 334a - and how to use it
    ... > clue how to use in the distortion analyzer mode. ... Set up the UUT to produce a sine wave at some frequency, ... player should be flat 50-15 Khz within 0.2 dB or better ... Apply the test signal and adjust the gain of the UUT to ...
    (rec.audio.pro)
  • Re: Low distortion sine wave VCOs - state of the art?
    ... The 8038 sine wave VCO has been around for a good chunk of a century. ... and I'm desiring a low distortion sine wave ... voltage, not a number. ...
    (sci.electronics.design)
  • Re: audio amp adjust
    ... Just feed it a sine wave into a dummy load. ... Adjust for minimum distortion. ... > some amount of cross-over distortion in excess of factory specs..... ...
    (sci.electronics.repair)
  • Re: "all pass" thought about (analogue) compression
    ... Assume that the sine wave we start with is 300Hz. ... A phase shifter can be made with a Q such that the ... If more distortion can be lived with, a lower power such as could ... the harmonics of the frequencies above 1KHz. ...
    (sci.electronics.design)