"Internal Signal Routing The SK-1 has 4 voices and percussion. Each voice is made up from an audio signal and an envelope control signal, which are combined to give the end voice. This module allows you to switch on or off any of the 4 voice audio paths, any of the 4 envelope control signals and the percussion. The patch panel then lets you have for instance, voice 2 under the envelope control for voice 4. You can then patch the percussion audio into the envelope control for one of the voices, which gives sustain effects or patch it into the audio signal and it gates the percussion with the keys, so the percussion sounds only while a certain voice is active. You can even swap the audio and envelope control signals over, which gives a buzzing / click type noise when you press a key.
Audio Filters / Level This module modifies the filters where the envelope control signal and the audio signal are combined to make the end voice. The knob is in 2 stages where it controls the level of the audio signal, but keep turning it and it then affects the filter. The control will take the tone and ‘squash’ it so for instance the bass line in the demo song, rather than a contiuous note turns into a blip, or stacatto effect. Very hard to describe but appears in the video at 2:28 sounds a bit like it is playing backwards. There is a knob for each of the 4 channels, and another knob for patching. The patch knob connects to 2 patch points, the idea is that one side connects to anywhere on the signal routing module, and the other goes off to the main patch panel allowing all the digital signals to be combined with the audio ones. In the video it is applied to the bass line and removed at 2:09 which gave it a ‘metalic’ twang, but that just depends where you plug the patch cables in.
Outputs This module brings all the 4 voices and percussion sounds and a video signal to the outside world. The SK-1 has lots of low pass filters / anti-aliasing filters inside before the final sound reaches the speaker / rear connector jack. The connectors on the top are pure unfiltered audio, which sound much brighter and if you are lucky enough to have a good mixing desk you can add your own EQ / FX to each voice. Likewise Casio have heavily attenuated the bass audio in the accompiamnents but now you just take it at any level you want from channel 3.
Pitch and Video This module gives overall pitch control for the SK-1 and deals with video generation. The pitch control raises the pitch and has it’s own on / off control. The video control is on/off and contrast, plus a patch input. If you patch a signal from the main patch panel, it combines it with the video ouput giving a range of displays. It also alters the sound when patched in, as the data signals are now going through video circuitry it creates glitchy patterns, weird notes etc.
Patch Panel This is the core for all SK-1 circuit bends, a lot of bent SK-1’s have a load of switches attached, the switches all connect to the RAM and ROM inside the keyboard to alter the sound. Here there are no switches, it is up to you to patch a wire across or use the bend sequencer. The patch panel has 25 connection and it mirrors the RAM and ROM address bus and data bus, plus a few other signals. You can link 2 or 3 points out directly, wire them across to the signal routing patch panel or sequence Bend Sequencer This allows you to automate the patch panel. When switched on, each LED lights in turn, and the patch connector below each LED becomes active. If you connect any of these to the patch panel, when the LED lights up it energises the patch panel switching the bend on and off. Depending on how many of the 10 auto bends and where you put them, you can have gentle modulations to the sound ( at the end of the clip there are some block chords with a gentle auto bend applied ), or severe random noise mayhem
