[Ardour-Users] MIDI workflow

Edward Diehl diehl at umich.edu
Mon Oct 17 10:38:37 PDT 2011

I've also been wondering about the best workflow for midi work.  I
want to record solo piano using Pianoteq and possibly other sounds
using Linuxsampler or Yoshimi.  That is, I'll use the same midi track
to drive 1 or more sound generation programs.  I find that the CPU
requirements of doing midi seem to be quite high so I've decided that
the best approach is to do a 2 step process:

1)  Sequence my midi track using just A3 and Pianoteq and no effects.
    do all the midi takes, editing.  Use low latency since audio is

2) "Bounce" midi to audio tracks (with Pianoteq, Linuxsampler, etc)
   and then mix/master those.  Might even bounce to Mixbus since I own
   it already.  Use high latency to minimize DSP demands.

Initially I tried working with a midi track + audio buses like this:

a3 midi track -> Pianoteq -> a3 bus -> a3 master
a3 midi track -> Linuxsampler -> a3 bus -> a3 master

I could add fx to either the bus or the master.  The above set up
requires routing midi and audio externally of Ardour using Jack,
though I don't think that is a big issue.  I'll automate the setup
using a scripts start all the programs I'm using and use aj-snapshot
for the Jack connections.  One issue is that when recording midi you
need to use low latency (I'm running at 8.7 ms) so you can monitor
properly.  The low latency makes the DSP problem worse.

Below I have some results about the Ardour3 CPU requirements.  The CPU
usage I gauge from the Ardour DSP number.  I have found that if the
DSP reaches 100% bad things happen, like lots of xruns.

Here are some measurements of Ardour DSP using Ardour3 Alpha10

Setup is:
a3 midi track -> Pianoteq -> a3 bus -> a3 master

DSP requirements 
                       IR EQ LS LS+EQ
Just playing      45%  54 67 82  92
Play + record     57%  65 75 92  99
Playback          50%  60 72 88  99

IR = Add IR plugin on master track 
EQ = Add LinuxDSP MKIIGraph EQ on Pianoteq bus
LS = Add LinuxSampler bus.  Route midi also to LinuxSampler playing
     SalamanderGrand and make new A3 bus for it.
LS+EQ Add LinuxDSP MKIIGraph EQ on Linuxsampler bus

DSP varies a bit for above measurements.  Seems to go up if you play
faster.  You can see that I run up against overloading the CPU when I
drive 2 audio buses from a midi track with a few fx.  Hence, I've
decided that I need to do midi recording and audio mastering in the 2
step process I mentioned above.

My laptop is a Dell 1420 with Intel Core2Duo T7100 1.8 GHz. 

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