Re:Was- Sooperlooper or Mobius? now Midi Latency

[andy butler <akbutler@tiscali.co.uk>]

Jeff Larson wrote:

> Finally there is latency getting the MIDI message through the device
> driver, OS, and finally to the application.  I've always thought this
> was much less than audio latency but I've honestly never tried to
> measure it.  

A lot of keyboard players use softsynths, and don't seem to suffer
too much from latency. 



> 
> So if the FCB were plugged directly into a USB MIDI interface I would
> estimate 1.5ms or 66 samples at 44.1K as a starting point and tune
> from there.
> 
> I remember reading a web page awhile ago where a guy described a
> process for accurately measuring MIDI latency.  He took a keyboard or
> some other device that would emit sound with close to zero latency and
> would also send a MIDI message. 
> 
> I suppose we could try something similar with footswitches: stick a
> mic near the switch, digitally record the mic and the MIDI it sends.
> The trick will be to locate the position in the recorded wave that
> represents "full down" since there will be some swishy mechanical
> noises as the switch travels down.  Sounds like a great project for a
> rainy day! :-)

shame on me, I had a rainy day when checking the Gordius LG.
Just triggering loops from the edp (no pc buffers involved).
Used a mic to record the sound of the press,
and also recorded the loop that was triggered by that midi note.
So total measured delay (4mS)included the edp response time, which 
is at least 1mS.

With, it was fcb1010 was 5-6mS or so.



> 
>>  From my limited software looping experienceI think it's worth 
>>   mentioning that when the player is monitoring 
>>    through the pc (e.g. when using amp sim software ) that the 
>>    easiest approach is to set the latency compensation to zero.
>>    (with possibly a tweak somewhere to account for the lack 
>>     of midi latency)
> 
> Yes.  When you monitor through the computer latency compensation needs
> to be done differently since the player is doing part of it mentally.
> I don't think Mobius does this correctly yet, I've been
> meaning to revisit this for awhile now but it seems that most people
> don't monitor through the computer.
> 
> Setting both input and output latency overrides to near zero is necessary
> for overdub alignment, but strictly speaking I think there is still
> be a need to compensate for MIDI latency.  The player may not always
> adjust the timing of footswitch presses in the same way they adjust
> instrument manipulation.  This could cause a situation where input
> latency compensation needs to be NEGATIVE, which would require a short
> "history" buffer.

Yep, I just turn off the looper latency compensation in this situation.

Then the midi delay is actually less of a problem than with hardware.

> 
> Likewise when you start doing things like loop triggering with a
> footswitch, output latency is still relevant.  So it feels like to be
> pedantic about it we need more knobs.  Maybe two output latency
> settings, one for overdub alignment and one for "jumps" in playback.
> I honestly haven't thought this through yet.

If your going to be retriggering loops and play live, then to monitor 
though the pc
has the advantage that the brain can do the compensation.
Just a matter of getting the total pc latency down to around 10mS, so 
audio in latency
is similar to midi In latency.
(as consciousness is around 500mS behind reality anyway, 
  that shouldn't be a problem)

> 
> Jeff
> 
andy