How is a quasi-stereo field created by processing mono? at DVinfo.net

David Ennis · July 26th, 2005, 08:46 AM

LIke many home audio systems, my Altec Lansing computer speaker system has a switch to add a stereo-like spaciousness to mono sound. It sounds really good. I don't mean reverb, but rather what seems to be a frequency crossover formulation.

Does anyone know what's being done to the signal to produce this effect?

Steve House · July 26th, 2005, 09:39 AM

I don't have it with me so I can't quote the procedure but I seem to recall Jay Rose's Audio Postproduction book has a section on how to create quasi-stereo from a mono signal.

Gints Klimanis · August 10th, 2005, 08:01 PM

There are many methods. If it's in circuitry, it would probably be some complementary comb filter, usually implemented with all-pass filters.
The idea is that if you present each ear with a different set of frequency bands, you will perceive stereo. Decorrelation is the process, although I would call this local decorrelation. So, imagine the spectrum divided into bands. Odd bands go to the left ear while even bands go to the right ear.
Low freuencies are not spread in these circuits, as we are generally unable to localize them. If you want to test if this is the method, run a swept sine (sine wave gliding up in frequency) through your speakers. You should be able to hear the sine wave flip-flop between the speakers.

If you have a 31-band stereo equalizer, try boosting the left channel odd bands and right channel even bands. Then, cutting the left channel even bands and right channel odd bands.

July 26th, 2005, 08:46 AM	#1
David Ennis Fred Retread Join Date: Jul 2004 Location: Hartford, CT Posts: 1,227	How is a quasi-stereo field created by processing mono? LIke many home audio systems, my Altec Lansing computer speaker system has a switch to add a stereo-like spaciousness to mono sound. It sounds really good. I don't mean reverb, but rather what seems to be a frequency crossover formulation. Does anyone know what's being done to the signal to produce this effect? __________________ "Nothing in the world can take the place of persistence..." - Calvin Coolidge "My brain is wired to want to know how other things are wired." - Me

July 26th, 2005, 09:39 AM	#2
Steve House Inner Circle Join Date: Mar 2005 Location: Hamilton, Ontario, Canada Posts: 5,742	I don't have it with me so I can't quote the procedure but I seem to recall Jay Rose's Audio Postproduction book has a section on how to create quasi-stereo from a mono signal.

August 10th, 2005, 08:01 PM	#3
Gints Klimanis Inner Circle Join Date: Jun 2003 Location: San Jose, CA Posts: 2,222	There are many methods. If it's in circuitry, it would probably be some complementary comb filter, usually implemented with all-pass filters. The idea is that if you present each ear with a different set of frequency bands, you will perceive stereo. Decorrelation is the process, although I would call this local decorrelation. So, imagine the spectrum divided into bands. Odd bands go to the left ear while even bands go to the right ear. Low freuencies are not spread in these circuits, as we are generally unable to localize them. If you want to test if this is the method, run a swept sine (sine wave gliding up in frequency) through your speakers. You should be able to hear the sine wave flip-flop between the speakers. If you have a 31-band stereo equalizer, try boosting the left channel odd bands and right channel even bands. Then, cutting the left channel even bands and right channel odd bands.