Timecode abuse

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While playing back a multitrack tape, which includes a sequencer locked to
tape with SMPTE, I hit the varispeed button on the recorder for fun, and
noticed that although the tape was suddenly running around 15% faster,
the sequencer apparently kept perfectly in step (although it must be said, I
wasn't listening to the sequencer's output at the time).

How far out can SMPTE generally go before it can no longer cope?
For example, would it be able to lock against a stripe being played at
half speed, or double speed?
Could you use this kind of technique to lock two tape machines, with
one running at 7.5 ips and the other at 15ips?
(I may need to do this later.. and no, doing it digitally would be boring)

--
JP Morris - aka DOUG the Eagle (Dragon) -=UDIC=- jpm@it-he.org
Anti-walkthroughs for Deus Ex, Thief and Ultima http://www.it-he.org
Reign of the Just - An Ultima clone http://rotj.it-he.org
The DMFA radio series project http://dmfa.it-he.org
d+++ e+ N+ T++ Om U1234!56!7'!S'!8!9!KAW u++ uC+++ uF+++ uG---- uLB----
uA--- nC+ nR---- nH+++ nP++ nI nPT nS nT wM- wC- y a(YEAR - 1976)

Archived from groups: rec.audio.pro (More info?)

J. P. Morris wrote:
> While playing back a multitrack tape, which includes a sequencer locked to
> tape with SMPTE, I hit the varispeed button on the recorder for fun, and
> noticed that although the tape was suddenly running around 15% faster,
> the sequencer apparently kept perfectly in step (although it must be said, I
> wasn't listening to the sequencer's output at the time).
>
> How far out can SMPTE generally go before it can no longer cope?

That's a function of the device receiving the time code. Some can take
a pretty wide range, others are quite limited. 10% can usually be
expected, sometimes more.

But it sounds to me like the sequencer wasn't truly locked to time
code. It may have used the time code to know when and where to start,
and then was free-running on its own clock. A lot of digital devices us
that sort of "sync" but of course it can't respond to changes in speed
of the time code source.

You don't really want to do this with MIDI and a tape deck, though. As
you probably noticed, when you speeded up the tape, the pitch raised as
well as the tempo. But when you speed up the time code that the
sequencer is chasing, while it will increase the tempo, it can't do
anything to change the pitch since that's a function of the synth
hardware.

Hopefully you noticed that the tape and the synth were no longer in
tune.

Archived from groups: rec.audio.pro (More info?)

J. P. Morris <jpm@it-he.org> wrote:
>
>While playing back a multitrack tape, which includes a sequencer locked to
>tape with SMPTE, I hit the varispeed button on the recorder for fun, and
>noticed that although the tape was suddenly running around 15% faster,
>the sequencer apparently kept perfectly in step (although it must be said, I
>wasn't listening to the sequencer's output at the time).
>
>How far out can SMPTE generally go before it can no longer cope?

>As far out as the sequencer can go.

>For example, would it be able to lock against a stripe being played at
>half speed, or double speed?

Sure, that sort of thing is often done for rock videos where they do
playback on set at half-speed and have folks lip synch to it, for
weird speed-up motions while keeping lip synch.

>Could you use this kind of technique to lock two tape machines, with
>one running at 7.5 ips and the other at 15ips?

Sure, but if they're both running at the speed the stripe was laid down,
that isn't very exciting.

>(I may need to do this later.. and no, doing it digitally would be boring)

SMPTE _is_ digital!
--scott

--
"C'est un Nagra. C'est suisse, et tres, tres precis."

Archived from groups: rec.audio.pro (More info?)

Scott Dorsey wrote:
> J. P. Morris <jpm@it-he.org> wrote:
>
>>For example, would it be able to lock against a stripe being played at
>>half speed, or double speed?
>
> Sure, that sort of thing is often done for rock videos where they do
> playback on set at half-speed and have folks lip synch to it, for
> weird speed-up motions while keeping lip synch.
>
>>Could you use this kind of technique to lock two tape machines, with
>>one running at 7.5 ips and the other at 15ips?
>
> Sure, but if they're both running at the speed the stripe was laid down,
> that isn't very exciting.

The idea is to fly in a double-speeded tape to the multitrack, using SMPTE
both to lock the two together AND to control the sequencer when the track
is laid down on the other machine. So the stripe will be laid down at
15ips, the track recorded at 7.5 (this is the bit that may freak out the
SMPTE unit) and then the two decks will be locked together at 15ips.

>
>>(I may need to do this later.. and no, doing it digitally would be boring)
>
>
> SMPTE _is_ digital!

So is the control board on the tape deck, but likewise, that's irrelevant.
What I meant was recording the track digitally, doubling the speed digitally,
and then dumping it onto the multitrack.

> --scott
>


--
JP Morris - aka DOUG the Eagle (Dragon) -=UDIC=- jpm@it-he.org
Fun things to do with the Ultima games http://www.it-he.org
Developing a U6/U7 clone http://ire.it-he.org
d+++ e+ N+ T++ Om U1234!56!7'!S'!8!9!KA u++ uC+++ uF+++ uG---- uLB----
uA--- nC+ nR---- nH+++ nP++ nI nPT nS nT wM- wC- y a(YEAR - 1976)

Archived from groups: rec.audio.pro (More info?)

On Thu, 15 Sep 2005 03:45:34 GMT, in rec.audio.pro KenLac
<ainttellin@nowhere.com> wrote:

>Richard Crowley wrote:
>> Back in the good old days of video tape (before VHS and then
>> cassettes), big 2-inch quad reel-to-reel transports could "chase"
>> even during FF and Rewind.
>
>Yeah, but I'll bet that was based on "tach" pulses rather than pure SMPTE.
>
>If I recall correctly, the Studer 24 track machines would "chase" at
>high speeds by motor tach signals, and then, when it got close to the
>target the tape would come near enough to the heads to actually taste
>the timecode and bring it back to perfect sync. Up until that last step
>it was just guessing how many revolutions of the motor it would take to
>keep it in sync.
Almost... The studerA80 TLS used the tach signals from the tape path
idler, it didnt have motor tachs.The tape tach was accurate to about a
second in a full reel of tape, so the timecode sync was reletive easy
to do.
One day there was a client who wanted a 4 tr Studer in a video
editing suite (1" C format days). So we got a CMX editor inteface,
glued it into a standard A80. That was so impressive, the studer TLS
was a donkey in comparison to the CMX.

end irrelevant ramble


martin