SQdecode v1.2

freeware quadrophonic sound decoder software
by /\/\arcus Junglas

Introduction

During the 1970ies there was a wave of quadrophonic vinyl releases, many used the SQ matrix system (Stereo-Quadrophonic) develloped by CBS. This system encoded two rear channels into a normal stereo sound. No special pickup was needed to play it back, but a SQ decoder amplifier was needed to decode the sound and to feed four speakers.
In the end the quadrophonic revolution never happened and it was forgotten. Only quad recordings survived, some SQ encoded music even found its way on CDs, e.g. Mike Oldfields 3-CD set "Boxed" and his live recording "Exposed".
With todays DVD technology multichannel music comes up again and it seems like it might have a better impact this time. Lots of multichannel amplifier are sold. Unfortunately no SQ decoding circuit was implemented into modern amplifiers, although it's just a matter of software/firmware.
 

What is SQdecode?

SQdecode uses a WAV file as input and decodes the quad matrix and then outputs either four WAV files or a quadrophonic WAV file. This could be used to feed a multichannel amplifier or to be again encoded to Dolby Digital or dts using a third party encoder (just to mention one: have a look on the Surcode dts encoder). So it is possible to create a multichannel dts CD which can played back on any CD player if it is connected digitally (SPDIV, optical cable) to a dts capable amplifier.
Of course it is possible to listen to the result using any WAV player and to check out if there are differences in the "mix".

SQencode also allows a post decode channel mix as done in some real quad amplifiers. This improves front-back channel seperation for the price of a little left-right seperation. My tests showed that some mixing really improves the overall surround feeling.

SQencode performs a -90 degree phase shift as part of the SQ matrix decoding process. For experimental use any WAV can be run through the phase shifter stage.

Here is a screenshot of SQdecode:

Does it sound good ?

SQdecode uses a 500 point Hilbert filter and 64 bit sample precision for the complete calculation. Both values are high enough to be sure of a clean calculation without artefacts. The frequency range is linear over full spectral range, a lot better than possible on any real existing SQ decoder/amplifier.
On the other hand this makes SQdecode quite slow. It needs about twice the playback time on my Athlon 750 MHz. I'll try to speed it up in the future.

I just want to mention here, that the whole SQ matrix system is far from being a real discrete multichannel format. The possible channel seperation is low (about 3dB), it's just possible to put some emphasis on certain instruments. Impressive sound effect like in todays movies are not possible.
Anyway, the effekt is audible and makes it sound interesting.
 

What does it cost ?

Nothing! It's Freeware. Use on your own risk (is there any?). ;-)
Just download the package here (SQD12sfx.exe, 230 kB). This is a self-extracting archive. Execute and unpack all files to a new directory whereever you like. The package includes the programm file plus documentation. SQdecode does not need any installation nor does it write any system files (no registry access, no DLLs somewhere in your system).
 

Contact

For feedback and bug reports just click here and send an email.
Please do NOT write to me to find any SQ encoded material or any software to handle the output of SQdecode, e.g. any Dolby Digital or dts encoder! This isn't my business.
 

Happy decoding!

/\/\arcus