Editing Using the FV-1 simulator

The [[Using the Sandbox FV-1 Editor|Sandbox FV-1 Editor]] includes a software model of the FV-1 chip.  Your assembled program runs through it in real time, so you can hear an algorithm on a test tone, an audio file or live input before you program any hardware.

Open it with the '''SIM''' tab on the right-hand edge of the editor.

== Getting sound out of it ==

# Assemble your program.
# Press '''Load Current Build''' in the Program section.  The state indicator changes from ''Not loaded''.
# Choose an input under '''Input Source'''.
# Press '''Play'''.

Leave '''Reload simulator on each assemble''' ticked and every successful build drops straight into the running simulator without interrupting playback.  This is the fast way to work: edit, assemble, listen, repeat.

'''Reset''' stops playback and clears delay memory.  Reach for it when a program has filled the delay line with something horrible and you want a clean start.

== Input sources ==

{| class="wikitable"
! Source !! Good for
|-
| Sine tone || Filters, pitch effects, anything where you need to hear one frequency clearly.  The frequency slider covers 20 Hz to 8 kHz.
|-
| Sawtooth / Square || Harmonically rich material — filters and distortion show their character better than on a sine.
|-
| White noise || Filter shapes and reverb tails.
|-
| Audio file || Load a guitar DI or drum loop and hear the effect in context.
|-
| Live input || Play into it through your audio interface.
|}

== Pots ==

The three sliders map to '''POT0''', '''POT1''' and '''POT2''' exactly as the physical controls do on the pedal, and they update while the program is running.  If your algorithm reads <code>POT0</code>, moving the slider changes it live.

== Levels ==

'''Input''' and '''Output''' trim the signal either side of the simulated chip, in dB.  Input defaults to −6 dB.

This matters more than it sounds.  The FV-1's accumulator saturates, and the simulator models that saturation, so an input that is too hot will clip inside your algorithm in the same way it would on hardware.  If something sounds unexpectedly crunchy, pull the input level down before you go hunting for a bug in your code.

'''Bypass''' passes the dry signal through so you can A/B against the effect.

== The crystal setting ==

The '''Clock''' section changes the rate the simulated chip runs at, the same way swapping the crystal does on real hardware.  The standard FV-1 clock is 32.768 kHz.

Your program does not change — it still runs 128 instructions per sample.  What changes is everything measured in samples:

* Delay times scale with the clock.  The FV-1 has a fixed 32768 words of delay memory, so a faster clock buys you proportionally ''less'' delay time.  The readout under the selector shows the maximum delay and Nyquist frequency for the rate you have chosen.
* LFO sweeps scale too, so a chorus tuned at 32.768 kHz will modulate faster at 48 kHz.

Changing the crystal rebuilds the audio engine, which clears delay memory.

== What the model does and does not get right ==

The simulator is faithful about the things that give the FV-1 its character:

* 24-bit accumulator saturation.
* The 14-bit companded delay memory — the reason FV-1 delays sound the way they do.
* LFO rates and depths, following the equations in Spin's application note AN-0001.

One approximation to know about: the fractional interpolation inside <code>CHO</code> is approximated rather than modelled exactly.  Chorus and flange will sound right, but they will not match hardware sample for sample.

'''Always confirm a design on the real pedal before you ship it.'''  The simulator is for iterating quickly, not for signing off.

== See also ==

* [[Using the Sandbox FV-1 Editor]]
* [[Writing your first FV-1 program]]

[[Category:How-to]]