RE: laptop setup: unwanted clicks

["jeff larson" <jeff.larson@sailpoint.com>]

> From: nico spahni [mailto:nicosp@gmx.net] 
> 
> I've been experimenting with a laptop looping setup (Apple 
> G4/1.25, RAX, Sooperlooper, various plug-ins).
> 
> Basically everything works pretty fine if it weren't for 
> those unwanted clicks that make themselves heard every now 
> and then. I haven't figured out yet when exactly they happen 
> - not necessarily when I change a setting or hit a button.
> 
> Does anyone know what I'm talking about? What is the source 
> of these artifacts?

The most common reason for clicks is that your audio block size (and
therefore your latency) is too low.  I'm not very familiar with Apple
audio, but somewhere there should be an option to select a block size,
typically with numbers like 128, 256, 512, 1024, etc.  Select the next
higher number and see if the clicks go away.

The issues around block size and latency are complicated.  Basically
the sound card is constantly asking the audio application for a small
block of samples to play.  The application has to fill this block in a
very small amount of time, a few milliseconds.  If this block cannot
be filled within that time, you "miss an interrupt" and there is a gap
in the audio stream which sounds like a click.

There are many factors that affect how long it takes an application to
fill this block but mostly it is the speed of the processor, and the
number of other plugins or applications you have running at the same
time.  The more plugins you try to run the slower the application
becomes and the more likely you are to miss an interrupt.  Some
plugins are faster than others, delay effects are usually pretty fast
but complex ones like convolution reverbs are very slow.

If you can't tolerate the higher latency caused by larger block sizes,
then the only option is to reduce the number of plugins you're
running.  Of course you have to be careful about non-audio
applications that are also running.  Don't be surfing the net or
defragmenting your disk while you run an audio app.  Everything else
should be shut down.

The second most common reason for clicks is simply software bugs.  If
it is a software bug, the clicks usually happen regularly, like at the
start point of the loop, or after a certain function is performed.  If
the clicks happen at random it is probably due to latency.

Jeff