Amiga Computing - Commodore Is Awesome

Some advice from
Paul Overaa on
eliminating
sequencer
timing problems
Most musicians ai some time or other
will need to transfer sequences to
their Amiga from an external Midi
■■■■■ unit. This could be a drum
machine, a standalone sequencer that uses
'mini' disks rather lhan the 3 1/2" variety or
some other unit where it's not possible to use
the standard approach of saving the sequence
as a Midi file and loading it direclly into the
Amiga. In all such cases it then becomes neces
sary to link the external unit to your Amiga (via
a Midi coble] and physically transfer the song
sequences by ploying them on the source
machine whilst recording the output.
The one thing you shouldn't do is try and
adjust the playing and recording speeds manu
ally. No matter how careful you are in adjusting
the tempo settings you are unlikely to get it right
and a 120 bar source sequence might end up
becoming anything between 119 and 121 bars
in length. Whilst this will not affect the playback
of the new sequence it will make sequence edit
ing a nightmare because the original bar divi
sions present in the sequence are destroyed.
Fortunately the solution is easy. Set up the
external device so it generates Midi clocks and
then arrange for the sequencer doing the
recording to use those clock messages rather
lhan following its own internal timing clock.
Almost all Amiga sequencers hove menu
options for using an external clock in this way.
Some, such as Dr T's KCS, even provide con-
Irols which allow you to choose whether an
explicit Midi Start message is needed to make
the sequencer begin recording or whether it
should start as soon as the first clock is
received.
These features are not always needed but
can be handy when you're dealing with an
external Midi device that generares timing
clocks continuously (some old drum machines
had an annoying habit of doing this even when
a drum pattern was not playing].
So to record from any external unit you firstly
set it up so it will generate timing clocks whilst
ploying and then load up your sequencer pro
gram and select the external clock option. Set
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Dr T's KCS sequencer can either wait tor real Midi 'start'
messages or starting recording on the first received Midi clock
Amiga Computing
MARCH 1997
Recording rhythm patterns from this Yamaha RYB drum machine is
a prime candidate for using your sequencer's external clock option
the sequencer to record, hit the start button on
the external unit - you'll find the sequencer will
record the sequence exactly as it wos written
without any bar length timing glitches in sight.
In case you're wondering how all this techni
cal magic works here's a brief run-down on
what happens beneath the surface; Midi clocks
are single byte Midi messages that have the
value decimal 248 (that's F8 hex). When you
set a sequencer to its external clock option the
internal timing mechanism is disabled and atten
tion is focused purely on the incoming Midi
data.
The external device will be transmitting clock
bytes at the rate of 24 per quarter nole and
these will be received along with all the other
Midi data. Whenever the sequencer reads one
of these clocks it adjusts its bar position counter
by l/24th of a quarter note. By the time 24
have been collected the sequencer will know
that one bar of data has been received.
When you record data in this way the
absolute tempo of the external device doesn't
really matter. To double the playing speed you
double the number of Midi clo:ks sent. Halve it
and you halve the number of Midi clocks. Either
way the sequencer will be aole to recognise
each bar of music as it arrives and if, for exam
ple, you play exactly 120 bars of a sequence ■
you will end up recording exactly 120 bars
regardless of tempo.
These type of external clock based Midi links
Linking Two Amigas
also come in useful on other occasions. You
might come across a collection of songs record
ed with an old sequencer which didn't provide
options for exporting sequences as Midi files.
To move those songs across to a more mode'n
sequencer you just need to borrow another
Amiga and link the two machines together
using a Midi connecting lead (and two Midi
interfaces].
Once you've linked the source and destina
tion machines together and loaded the respec
tive sequencer programs, do pretty much the
same thing as before: Set the sequencer that is
going to play the song sequences to its internal
clock option, making sure that it is also set to
generate liming clock messages at the same
time. Then set the sequencer being used for
recording to its external clock option and start it
recording.
Nothing will actually happen until the source
sequencer is started. This is because the
recording sequencer will be waiting for ihose
all important Midi clocks and these will not
appear until the sequencer being used lo play
the song is actually started. When you do hit
the source sequencer's start button however,
everything should foil into place. The destina
tion (recording end) sequencer will then record
and store a copy of the original song material
bar for bar.