Transform highZ speaker out from 16mm projector to mediumZ mic in of camcorder?

Question

Just going straight from the projector's 1/4 inch speaker out (the speaker out has a fixed volume-no volume control. It's a telex instaload telecine) to the camcorder's 3.5mm mic in gives me an audible but loud and distorted sound signal. I bought a high-low transformer (Shure A85F). This corrected the distortion in the sound, but there is a loud hiss which gets much louder when the soundtrack goes soft and diminishes somewhat when the soundtrack is at a high, but never completely goes away. Is there another kind of high-low transformer that's stronger or more appropriate? The Shure A85F's specs say it has "24db of voltage gain." Should I look for a transformer with a higher db voltage gain? Please help me lose the hiss. Thanks.

Answer 1

Your transformer seems to be doing the right job. The hiss is most certainly coming from the film sound track. The projectors audio system has a built in AGC circuit, so that it pumps up audio (including hiss) in the quiet sections. You will need to process the audio later in the computer to reduce the hiss (high frequency cut), and restore dynamic range.

Answer 2

I'd put all my bets that the culprit AGC is in the camera and not the projector. That's why consumer camercorders' audio sucks. Your transformer is doing its job, the camera is trying to compensate for the quietness and increases the recording level... these Automatic Gain Control circuits are dumb and can't tell hiss apart from meaningful signal.

If you have an option in the camera to switch to manual recording levels and turn off AGC, by all means.

In addition, you might also wanna try a -40dB pad (attenuator), that's more suit for the job than the A85F.