Subject: Re: [linux-audio-dev] Final Scratch, custom kernel?
From: robbins jacob (jacobrobbins__AT_hotmail.com)
Date: Tue Oct 08 2002 - 06:32:56 EEST
Interestingly enough, the FinalScratch system does not allow cueing to
different positions in the record by lifting the needle up off the record. I
saw Richie Hawtin playing on one in DC and I didn't realize what it was at
first. I was really perplexed because it seemed like everytime I looked up
he was just at the beginning of a record: the tonearm was always very far
out towards the edge of the record. Then I figured out that he was using
final scratch because he was picking the tracks from a laptop nearby running
a program that was basically two lists of tracks. I didn't even think the
position signal was running through the audio, I thought they had a separate
system magnetically measuring the record position. But it must be something
like the saw tooth signal described in this discussion.
I wouldn't worry too much about using the cueing of the needle on the
record to move through the track. It's more useful on a real record because
different sections of a track actually are visible to the naked eye on black
vinyl, which jogs your memory into remembering the layout of the track. The
final scratch record must have a single loop out at the edge of the record.
Such a loop is called a locked-groove when put on a real record: certain
styles of dance music have a convenient bpm that allows putting a complete 4
bar pattern into one seamless loop towards the end of the record (the
middle). I've only encountered this in techno tracks. There can be a
complete track which ends by moving into the lock groove which plays
endlessly until the dj stops the record. The beat must perfectly fit one
rotation of the record in the lockgroove or else the rhythm will be broken.
The same constriction applies to making a lock groove of a control signal. I
am convinced final scratch records have a few locked grooves of a control
signal at the edge of the record.
Adding positional cueing would be a nice feature but consider some of
the following circumstances: -you have to put a lock groove at the end of
the spiral groove anyway or else you limit the length of track that you can
control to some arbitrary amount of time. -if you try to get around this by
making a 30 minute track you'll find that the groove is cut smaller so that
the record will wear faster and will skip much easier when you scratch it.
This is why dance singles have one 6-10 minute track cut on the entire side
of a 12" record; record wear is a factor for a dj playing a track many times
and bigger grooves hold up longer to repeated playing. They will also sound
better longer which is not really an issue here. records tend to wear by
pushing towards the outside of the groove from centripedal acceleration. -if
you make a 10 minute position-coded section leading into a lock groove you
will have to have the standard width of the 10 minute section map to the
length of the entire track being played. This means that moving the needle
to the middle amounts to saying "move 50% of the way through the track"
(which is pretty useful). But it's probably going to end up being easier to
cue through the software. Hell it will be easier to do everything through
the software. The only advantage I see a turntable controller having is for
scratching effects and for dj's who don't want to carry a lot of records.
And maybe for beatmatching audio files but programs are leaning towards
doing that ahead of time (GDAM). As such I wouldn't worry too much about the
positional thing, in favor of getting very tight velocity response for
scratching and beatmatching. 8 ms will kill you in beatmatching and final
scratch has to have closer than 8 ms "grip" on the audio file being
controlled. ~4 ms off is audible phasing. I think it's very interesting to
investigate it but it might be easier to just cut a lock-groove control
signal and not bother about encoding digital signals on a record.
---jacob robbins;;;;;;;;;
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