User manual

Filter CV In for Devil Fishes prior to 2.1C

With versions 2.1A and earlier, this input had an unloaded voltage of about 1.0 volts.

Applying a voltage below this would lower the filter frequency. With version 2.1B, the

unloaded voltage was about 3.7 volts. Any voltage below this will lower the filter

frequency and any voltage above this will raise it. The 2.1B arrangement is a lot more

sensitive then 2.1A – a given range of input voltages will achieve a wider variation of

filter frequency. For voltages below about 4.2 volts, the sensitivity is about twice as

sensitive. Above 4.2 volts it is about ten times as sensitive. This enables finer control of

lower frequencies, whilst still allowing for very high filter frequencies. Like the other CV

inputs, any input voltage in the +/- 15 volt range is safe. Probably a 0 to 10 volt range is

ideal for driving the Filter CV Input.

Version 2.x Devil Fishes prior to 2.1C had linear responses to the external CV (albeit

with two slopes in 2.1B). This the system more musically sensitive at lower filter

frequencies compared to higher ones. Version 2.1C and later has an exponential –

approximately 1 volt per octave – response. This means that whatever frequency the

filter is with in input of, say, 3 volts, it will be at twice that frequency with 4 volts, and

four times that frequency with 5 volts etc.

Filter Tracking pot

The voltage to frequency function of internal Filter Tracking pot is linear. While the pot

is a log pot, which I have made a little more linear, the relationship between the internal

CV (from the internal sequencer or external CV In) and the filter frequency is linear in a

volts to Hertz sense. So, for instance, with a particular setting of the Filter Tracking pot,

and the CV (from an external source, or the internal DAC, as driven by the internal

sequencer or MIDI In system) equal to say 2 volts, and with all the other settings (Cutoff

pot etc.) the filter might have a cutoff / self-resonant frequency of say 1 kHz. With a CV

of 3 volts this would become 1.5 kHz, with 4 volts it would become 2 kHz and with 5

volts, it would become 2.5 kHz. The result of the linear system is that high notes (CVs

of 3 to 5 volts) lead to only moderate increased in filter pitch (when considered in octaves

or semitones), while low notes (1 to 2 volts) lead to dramatic drops in pitch (again when

considered by an exponential scale such as octaves or semitones).

I tried an exponential (logarithmic) approach (1 volt/octave and beyond, to 0.33

volt/octave – as is typically found on other synthesisers) and decided the linear approach

was much more interesting.