HVM

Human Voice Module - fixed filter bank

The 8HP wide Oakley Sound Human Voice Module (HVM) is an all analogue audio signal modification unit that replicates some of the sounds made from a classic electronic keyboard first seen and heard in 1979. The VP-330 is often thought of as a string synthesiser and vocoder but some of its most ethereal sounds utilise its four human voice settings.

The human voice sounds of the VP-330 were created by using seven fixed frequency band pass filters - each of its four preset voices using differing mixes of the seven filters and different octaves from the keyboard's oscillators.

The HVM recreates these filter sections and arranges them in a flexible fixed filter bank format. All seven filters are presented with the same input signal, its level controlled by a single pot, Level. The output of each filter is sent to its own level pot and then mixed with the other six filter outputs to make one single output. Each filter section consists of two narrow band pass filters of slightly differing frequencies in series. The operating frequencies are 220Hz, 330Hz, 600Hz, 910Hz, 1300Hz, 2800Hz and 3300Hz.

Any type of signal can be processed either single notes or, if you have the polyphony, full chords can be used. It is best to use an harmonically rich waveform, such as a sawtooth or square wave, to give the filters something to work with.

The original design used seven bandpass filters with the lowest two bands having very similar operating frequencies, 185Hz and 220Hz. In the suggested build of the HVM Oakley have made them further apart, 220Hz and 330Hz, extending the usefulness of the module. However, an alternative build is possible that recreates the original behaviour if needed.

www.oakleysound.com/hvm-e.htm