Editing Writing your first FV-1 program (section)

== Step 3: an LFO ==

A tremolo is a volume control that moves on its own, so the next piece is a low-frequency oscillator.

The FV-1 has two sine LFOs (<code>SIN0</code>, <code>SIN1</code>) and two ramp LFOs (<code>RMP0</code>, <code>RMP1</code>).  You start a sine LFO with <code>WLDS</code>:

<pre>
WLDS	SIN0, 40, 32767		; LFO 0: rate 40, full amplitude
</pre>

This only needs to happen once, not on every one of the 32768 samples per second.  The idiom for that is a conditional skip on the <code>RUN</code> flag, which is clear on the very first pass through the program and set on every pass after:

<pre>
SKP	RUN, loop
WLDS	SIN0, 40, 32767
loop:
</pre>

On the first sample, <code>RUN</code> is clear, so the skip does not happen and the LFO is set up.  On every subsequent sample the program jumps straight over <code>WLDS</code> to the <code>loop</code> label.

To read the LFO's current value, use <code>CHO RDAL</code>:

<pre>
CHO	RDAL, SIN0	; ACC = the sine LFO, swinging -1.0 to +1.0
</pre>