DIY 16mm optical sound recorder, v2:

Darkroom setup and recording.

The digital audio file should be mixed according to the frequency responce curve (see results), and copied to a media player souch as a cell phone or an mp3 player. Here is a helpful link on mixing on the filmlabs network.

Next, the projector should be prepared in three steps:

remove the exciter lamp
place the modulated sound lamp on top of the sound lens
unscrew the exciter lamp fuse on the back of the projector to disable the pilot light

Once the file is on the media player and the projector is prepared, input levels should be adjusted so there is no distortion. When you start the media player, turn on the sound level knob on the projector - the sound playing on the media player should (magically!) be heard from the projector speakers. This is because the light is modulated by the media player, and the photocell (onto which this light is faling) is converting these oscillations back to sound through the projector amplifier. This allows us to adjust the LM386 input levels and/or sound levels of the media player ‘by ear’, to have a full range without distortion and with good dynamics.

Now we are ready to start recording. This part is to be done in a darkroom with the safety lights on:

place the unexposed film on the supply arm, emulsion side up
thread the film through the projector
start the projector motor (be careful not to turn on the projector light!)
start the sound file on the media player

When the recording is over:

stop the projector motor
turn the device electronics off
cut the film at the sound lens
develop the film

Done. We have made a variable density soundtrack on 16mm film!

The film stock I used was Orwo PF2, developed in Dektol for 3 minuntes.

next: The results
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