[Vintage-Audio] Tascam Porta Ministudio 07?

[Roy Morgan]

>From: Philip Atchley <beaconeer@elite.net>

... a 4 channel high speed (3.75 IPS) DBX cassette recorder.  I'm
>particularly interested in the "Sync" function as I'm not sure how that was
>implemented in a cassette unit.

I don't know how the synch function was implemented in the casette 
recorder, but I can tell you a bit about how it was used in the film making 
process.  A frequency standard, usually crystal controlled, was used to 
drive the motor in the film camera.  There may or may not have been any 
signal applied to the film itself, but the frame rate was very accurately 
controlled.  As the film was shot, the separate sound recorder would run 
and record the scene sounds.

A tone was recorded on the magnetic tape at the same time.  This tone was 
similarly derived from a crystal oscillator. It may have been 60 cycles but 
I don't remember.  With the Nagra dual track recorders, there was a center 
track of much narrower dimension between the two audio tracks. This synch 
track got the pilot tone for later synchronization.

There may also have been a mark tone applied to the tape to allow 
synchronization of the film and sound.  This may well be what the Tascam 
recorder synch funcrtion does.  In some cameras a small lamp near the film 
gate lit up for two or three frames to mark the beginning of the segment. 
This mark tone (called start slate in some systems) was controlled via wire 
or by radio signal from the camera.  When the camera was rolled,  the 
recorder automatically started up and recorded a start slate tone on the 
main sound track.  The term "start slate" came from the traditional 
chalk-board like slate with clapper top bar upon which was written 
production, scene, and take information. The clapping of the par allowed 
visual and audible synch information on both camera and sound tape for 
later alignment of the picture and audio tracks.

During playback at the beginning of the editing process the sound was 
normally transferred to film sound stock. This is magnetic recording tape 
the same size and shape as the movie film, either 16 mm or 35 mm. It was 
used in film sound recorders, often made by the Magnetek company.  The 
pilot tone drove synchronizers in the quarter inch playback machines during 
transfer to the film sound rolls. This guaranteed that the sprockets in 
both the film and the film sound recorders could be electro-mechanically 
synchronized and would keep the sound and picture synchronized for the 
length of the movie.

The film editing and sound mixing process resulted in three spools of 
master material, two picture rolls to allow for cuts, fades, and scene 
overlaps, and one sound roll with the sound track.  The sound roll usually 
had one track but possibly more.  Creation of the final print master was 
done with all three rolls passing through the print machine to create one 
roll with the pictures merged and the sound track recorded on an optical 
track at the edge, or less commonly on a magnetic stripe at the edge.

If anyone is interested in a Magnetek 16 mm film sound recorder, let me 
know. I have one which needs an appreciative home.

Roy
Washington DC area

- Roy Morgan, K1LKY since 1959 - Keep 'em Glowing!
7130 Panorama Drive, Derwood MD 20855
Home: 301-330-8828 Work: Voice: 301-975-3254,  Fax: 301-948-6213
roy.morgan@nist.gov --