Calculating groove in LSDJ (Page 1 of 2)

Ahhhhh, I'm stupid, thanks a lot.  I can't believe I've used this thing for 6 years without knowing that!

this probably isnt helpful, but in my experience ive found thats its usually *much* easier to micromanage groove with cleverly placed D commands than with G. It seems like the processor burden is much smaller too.

This might help: http://packetsofknowledge.se/LSDj:Ticks_and_grooves

Don't feel bad. I've been using LSDJ for 6 years and I didn't know that either, haha.  TIL.

Also, I'm like Bright Primate--I often use D commands instead.

With the voice of Richard Stallman, "I'd just like to interject for a moment."

LSDj is nowhere near that accurate. It's using a 4096 clock as its tempo base, which is then divided down to the BPM. This means you can set the time between interrupts in increments of about 0.2 milliseconds. The error for the BPM value varies with the BPM. Higher BPM means lower accuracy. However, there is a trick in place to switch between different values on every tick to increase the accuracy. Which increases the accuracy a small bit.

A real world example: 128 BPM is a tempo that divides from the 4096 Hz clock, and is theoretically completely accurate (to the limit of the clock crystal's accuracy.) 129 BPM is a tempo that divides badly from the 4096 Hz clock, and the real world BPM turns out to be 128.805 BPM. This is 0.151% too low. This one of the worst cases. 130 BPM becomes 130.032 BPM, or about 0.0244%.too high. I think Johan may have made a mistake and meant to say that the worst case error is a factor of 0.005, or 0.5% off. That's still fairly good.

Edit: The algorithm seems to be more complicated than I thought, and the accuracy is higher than the calculations above.

Notice how I purposely used the word accuracy instead of precision. Precision is something different than accuracy. LSDj has a relatively bad precision, ie the time between notes may jitter such that the time between each note varies, even if the long term average converges to the 0.5% or smaller error. This is because the CPU may be busy doing other things when a timer interrupt happens. The culprit is typically kits as well high frequency vibrato, and not using these will reduce the jitter. I haven't made any calculations on the actual error from this but might do so in the future.

Last edited by nitro2k01 (Jan 20, 2013 2:36 am)

Huh! What are you syncing to that needs that level of precision? Just curious. Is it just to lock to grid in your DAW or instruments from other clocks?

I initially assumed that your post was something about the Zef thing you just did and having to sync 2 gameboy tracks, but as I understand it from what nitro is saying, while LSDJ tempos may not be accurate in an absolutely sense, they should be accurate to other instances of LSDJ (yes? no?)

Anyway, this is probably the most interesting conversation ive seen on cm.o for a while.

No James I'm doing some other stuff that's LSDJ plus MIDI drums.