RidgeRat

2006-03-26 22:48:21 UTC

Hi group. I'm a recently signed newbie. After some advice from Douglas,

the friendly list admin, I have posted information about a possibly new

algorithm for direct digital synthesis of pink noise. (Otherwise, you

can tell me about my re-discovery.) You can find the full exposition at

http://home.earthlink.net/~ltrammell/tech/pinkalg.htm

A little background: When searching the web for a pink noise generator

method suitable for semi-automated loudspeaker or microphone testing, I

found the "Pink Noise page" at

http://www.firstpr.com.au/dsp/pink-noise/

My initial joy at learning about the Voss-McCartney algorithm there was

quickly damped when I found that I did not get good quality results from

it. This is illustrated in the web page. Further study led to some

insights, and from there variations that I believe are improvements,

which is why I am here, where the experts lurk.

To summarize the page briefly --

Abstract. The Voss-McCartney direct digital synthesis algorithm

generates a noise process approximating pink noise, from an

equally-weighted combination of random white noise sources, on a rigid

updating schedule. It is conjectured that the rigid periodicity of the

updating explains spectral artifacts that prevent the method from

converging uniformly to a good approximation of the desired 1/f power

spectral density curve. Generalizing the method to an unbalanced

weighting of correlated random sources yields an algorithm that

produces relatively accurate approximations to the 1/f power spectrum

characteristic with fewer terms. There is roughly 0.15 dB approximation

error over a 7 octave range using six uniform pseudo-random variates per

output value. Useful results are obtained from as few as four uniform

variates per output.

If this sounds interesting, check out the page and feel free to comment

here. I'm especially interested in whether you observe the same results.

the friendly list admin, I have posted information about a possibly new

algorithm for direct digital synthesis of pink noise. (Otherwise, you

can tell me about my re-discovery.) You can find the full exposition at

http://home.earthlink.net/~ltrammell/tech/pinkalg.htm

A little background: When searching the web for a pink noise generator

method suitable for semi-automated loudspeaker or microphone testing, I

found the "Pink Noise page" at

http://www.firstpr.com.au/dsp/pink-noise/

My initial joy at learning about the Voss-McCartney algorithm there was

quickly damped when I found that I did not get good quality results from

it. This is illustrated in the web page. Further study led to some

insights, and from there variations that I believe are improvements,

which is why I am here, where the experts lurk.

To summarize the page briefly --

Abstract. The Voss-McCartney direct digital synthesis algorithm

generates a noise process approximating pink noise, from an

equally-weighted combination of random white noise sources, on a rigid

updating schedule. It is conjectured that the rigid periodicity of the

updating explains spectral artifacts that prevent the method from

converging uniformly to a good approximation of the desired 1/f power

spectral density curve. Generalizing the method to an unbalanced

weighting of correlated random sources yields an algorithm that

produces relatively accurate approximations to the 1/f power spectrum

characteristic with fewer terms. There is roughly 0.15 dB approximation

error over a 7 octave range using six uniform pseudo-random variates per

output value. Useful results are obtained from as few as four uniform

variates per output.

If this sounds interesting, check out the page and feel free to comment

here. I'm especially interested in whether you observe the same results.