Re: [Rosegarden-user] MIDI Latencies vs. Human Latencies

[Richard C. <spa...@ec...>]

On Tue, 28 Aug 2007 10:09:51 -0400, Abrolag  =

<ab...@us...> wrote:

> Interesting you come up wit 25mS. I seem to remember (dimly) reading
> that auditory response time was approximately 20mS

Response time is something else, and much slower.  Here's a script I mad=
e  =

to test response time.  It plays a drum after a random delay, and you  =

respond by playing any note, and after ten times it displays your averag=
e.

#!/usr/bin/perl
use Time::HiRes qw( gettimeofday );

sub militime {
   ($seconds, $microseconds) =3D gettimeofday;
   return $seconds + $microseconds / 1000000;
};

open MIDI, "+</dev/dmmidi"; select MIDI; $| =3D 1; select STDOUT;
   for ($i =3D 0; $i < 10; $i++) {
     while ('...') {
       vec($vector, fileno(MIDI), 1) =3D 1;
       if (select $vector, undef, undef, 2) {
         sysread MIDI, $data, 4096;
       } else {
         last;
       };
     };
     $wait =3D rand(7);
     select undef, undef, undef, $wait;
     print MIDI "\x99\x28\x64\x99\x28\x00"; $start =3D militime();
     sysread MIDI, $data, 4096; $stop =3D militime();
     $latency =3D int(1000 * ($stop - $start) + 0.5);
     print "Your reaction time: $latency miliseconds\n";
     $total +=3D $latency;
   };
   $total =3D int($total / 10 + 0.5);
   print "Average reaction time: $total miliseconds\n";
close MIDI;

Using that script, I get results like this:

Your reaction time: 233 miliseconds
Your reaction time: 219 miliseconds
Your reaction time: 164 miliseconds
Your reaction time: 190 miliseconds
Your reaction time: 210 miliseconds
Your reaction time: 254 miliseconds
Your reaction time: 214 miliseconds
Your reaction time: 228 miliseconds
Your reaction time: 212 miliseconds
Your reaction time: 206 miliseconds
Average reaction time: 213 miliseconds

The best I've managed to do so far is 135 ms.

As for my other script, I've become much better at timing with a small  =

amount of practice, and I've learned not to be 20 ms late every time.  I=
  =

also changed the script to create a graph, which looks like this:

-120
-110
-100
  -90
  -80
  -70
  -60
  -50
  -40
  -30 =3D
  -20 =3D=3D=3D=3D=3D=3D=3D=3D
  -10 =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D
    0 =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D
   10 =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D
   20 =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D
   30 =3D=3D=3D=3D=3D
   40
   50
   60
   70
   80
   90
  100
  110
  120

The '0' field contains values from -5 to +5, and the '-10' field contain=
s  =

values from -5 to -15, etc.  ...or something like that, since obviously =
-5  =

isn't counted in both of them, but I hate Perl's broken int() function s=
o  =

I'm not going to think about it.

Anyway, synchronizing to a sound is a lot easier than reacting to a soun=
d,  =

as most of those are within 25 ms, but my reaction time seems to be ten =
 =

times worse.

Here's the script that makes the graph:

#!/usr/bin/perl
use Time::HiRes qw( gettimeofday );

sub militime {
   ($seconds, $microseconds) =3D gettimeofday;
   return $seconds + $microseconds / 1000000;
};

open MIDI, "+</dev/dmmidi"; select MIDI; $| =3D 1; select STDOUT;
   $next =3D int(militime() + 1.25);
   $wait =3D $next - militime();
   select undef, undef, undef, $wait;
   while ('latencies are everywhere') {
     print MIDI "\x99\x25\x64\x99\x25\x00";
     $next +=3D 0.250; SELECT:
     vec($vector, fileno(MIDI), 1) =3D 1;
     $wait =3D $next - militime();
     next unless select $vector, undef, undef, $wait;
     $time =3D militime(); sysread MIDI, $data, 4096, length($data);
     for ($i =3D 0; $i < length($data) - 2; $i++) {
       next unless substr($data, $i, 1) eq "\x90";
       next unless substr($data, $i + 2, 1) ne "\x00";
       if (abs($next - $time) <=3D 0.125) {
         $latency =3D $next - $time;
       } else {
         $latency =3D $next - $time - 0.250;
       }; $msecs =3D int(1000 * $latency + 0.5 * ($latency <=3D> 0));
       $bucket =3D int(100 * $latency + 0.5 * ($latency <=3D> 0));
       $bucket =3D +12 if $bucket > +12;
       $bucket =3D -12 if $bucket < -12;
       exit if ++$buckets[$bucket+12] > 60;
       print "\e[d\e[2J";
       for ($i =3D 0; $i <=3D 24; $i++) {
         $v =3D 10 * ($i - 12);
         $v =3D substr('    ' . $v, -4);
         print "$v " . '=3D' x $buckets[$i] . "\n";
       };
       if (abs($msecs) <=3D 16) {
         print "\e[1;33mLatency: $msecs miliseconds\e[0m\n";
       } else {
         print "Latency: $msecs miliseconds\n";
       };
     }; $data =3D substr($data, -2) if length($data) > 2;
     goto SELECT;
   };
close MIDI;

I've noticed my scripts don't work while other MIDI applications are  =

running.  I suppose my scripts also won't work if anyone's keyboard does=
  =

"running status."