It is well understood that a VTPO is not like a CD playing organ music.  It is a musical instrument in its own right. To get the most out of your VTPO, it is necessary to provide as many speakers as space and budget allow.  Fortunately there are many inexpensive powered monitors that are compact and that sound quite good.

The reason that a pipe organ CD can sound wonderful on a set of stereo speakers while a VTPO cannot, stems from the fact that the pipes are mixed acoustically in the air before the microphone picks up the sound.  In a VTPO, the sounds are "layered" electrically.  Electronic musicians are very familiar with this and know that twenty violins layered sounds nothing at all like a sample of twenty violins playing together.  The former sounds tinny and ugly, while the latter is rich and sweet.

A VTPO with few channels will sound good when only a few stops are drawn, but as fuller and fuller registrations are employed, the sound will become more and more unpleasant.  This phenomenon was dubbed "signal mixing" by Dr Colin Pykett who has studied this issue extensively and described very well in his paper (hyperlinked at bottom of  this page).

Signal mixing is most objectionable when one has ranks that have similar harmonic structures that are rendered by the same audio channel.  Examples are VDO and Celeste, or Post Horn and Trumpet.  I have proposed four audio routing tables for a GSO VTPO ranging from 2.1 audio channels to 9.1.  The “.1” refers to the subwoofer channel (4) which is available with the “Bass Management” system featured on the M-Audio 1010LT audio card.  A number of GSO “project files” have been created to implement the various audio routings.  Every effort was made to avoid the worst signal mixing effects.  Each additional pair of speakers will bring very significant improvements in sound quality.  Even the smallest Walkers are sold with 24 speakers.  This has everything to do with the great sound these organs are famous for.

Choose the tabs for the four options.  The 9.1 channel system is exactly the one that the author is using for his VTPO.  Pairs of channels may be used for stereo samples or mono samples arranged C/C#, a technique some VTPO users prefer as a way to reduce Intermodulation Distortion (IM).

Joe Hardy