Spin Semiconductor

I'm trying to better understand the LFOs in the FV-1. Specifically what is happening behind the scenes. Does the SIN LFO get updated every sample? What is the resolution of it? For instance, if I set a very slow speed (0.2Hz or something) will I hear steps or does it calculate a new value for each audio sample?

Same for the ramp LFO... what kind of resolution does it generate?

I've been working on an FV-1 emulator for faster developing and testing of FV-1 programs on a PC. All parts of my "chip" except the LFOs are working, but I want to make sure that I model the LFOs properly. Any help would be appreciated.

Also, apparently the delay memory is not 24 bits. How is it actually encoded? I want to be sure to model this properly as well.

LFOs (SIN and ramp) are calculated every sample period so you shouldn't hear any noise. The equations for rate, etc. in the LFO PDF were derived directly from the hardware so they are representative of how the hardware works.

Delay memory is a floating point type format, 1-bit for sign, 4-bits for exponent and 9-bits mantissa. Expands to a 24-bit 2's comp number for use in the MAC/ALU. Since it is floating point when it is expanded you may need to fill LSBs with 0 to make it 24-bits. In the FV-1 the number is always considered to range from +0.99... to -1.00 so the binary point is always in the same spot so the 24-bit 2's comp number is always S.23.

Hi Frank,

Thanks for your help. I think that should help me make this work.

Also, without revealing too many secrets, is it possible to describe a bit about how the saturate/limit module works?


Cheers,

Andrew

That is actually one of the simplest items in the chip, basically a hard limiter. If value is > 0.99... set it to 0.99..., if < -1.0 set to -1.0

Aha! I had wrongly assumed it had some sort of knee instead of being a hard clamp.

Thanks for your help.