Film-Tech Forum ARCHIVE: Perspecta and the Academy filter.

This is topic Perspecta and the Academy filter. in forum Film Handlers' Forum at Film-Tech Forum ARCHIVE.

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Posted by Stephen Furley (Member # 1277) on 11-20-2013, 05:22 AM:

A few weeks ago somebody lent me a reel of film with Perspecta on it. I don't know what it was; it was in Japanese and had no subtitles. I tried connecting the Perspecta card so that the Academy filter was not in use, and there does seem to be sound on the track beyond the frequency where the Academy curve normally rolls it off. I took the top end down a bit, but from a higher point than the Academy does, and it sounds better than it does with the filter in. The Perspecta did seem to be reducing the gain in quiet scenes, thus reducing the noise. During most of the reel there wasn't a great deal of directional sound, but it still sounded better than a typical contemporary Academy mono track. Still nothing at the bottom end of course.

Were Perspecta tracks intended to be played with or without the filter?

Posted by Steve Guttag (Member # 268) on 11-20-2013, 06:49 AM:

WITHOUT. If you are using a CP200, in particular, the Academy filter has to be out or the CAT109 will also filter out much of the Perspecta control tones! (A proper academy filter has both HP and LP fitlers, not just the LP filter) Since the control tones can turn on/off the channels, yes, there will be a degree of noise reduction. Note, the control tones can also determine how loud each of the three stage channels are too.

Now, the film was still mixed to the rooms of the day so it is likely to sound a bit spitty on a fully tuned room with EQ. I did a bit of research on this with 70mm even...there was a discussion I had on whether format 40 70mm film should have an academy filter on them since no such specification was ever applied to the magnetic tracks, like they were with optical. The answer is yes, by the way. The academy filter is only there to "re-eq" a room that has extended frequency response so it mimics the response of the "typical" room of the day (before EQ and extended response) In fact, a studio, when recording the magnetic tracks may even apply boost in the recording to extend the response to compensate for the theatre's response.

I was able to prove this using two identical rooms...one with a circa 1957-1965 electronics/head end and one with modern (2005) electronics complete tuning. Running the same movie (same print), if you didn't have an Academy filter in...the new system sounded VERY shrill. Once the filter was in place...it sounded rather awesome, actually...it was cleaner than the old system, natural sounding...etc. It had all of the benefits of modern electronics (lower distortion, less noise) but with the proper response. We then converted the other auditorium.

So again, in Perspecta...you'd ideally have a filter after the B-chain to have it mimic the older auditoriums. I have not studied Perspecta that much to know if the various Perspecta boxes tried to extend response any. It is likely they may have had some sound "warping" filters in there too. For its day, it was rather sophisticated. Extra HF response would likely be perceived as more High-Fidelity.

Posted by Stephen Furley (Member # 1277) on 11-20-2013, 07:35 AM:

What's 40; is that the Todd-AO style non-Dolby version?

There's also a question of the hearing of the audience of course; at my age I've lost much of the top end of my hearing. It's not bad by any means, but it used to be very good when I was younger. I also have difficulty hearing direction in sound, which makes judging Perspecta or stereo systems a bit difficult now.

I suppose when Perspecta tracks were played in non-Perspecta houses the cut at the bottom end of the filter would have done much to remove the Perspecta tones.

Posted by Steve Guttag (Member # 268) on 11-20-2013, 12:06 PM:

The tones were below the response of the speakers of the day. Remember, optical sound has no problem with reproducing low frequency...so any quality of soundhead would be able to do it. However, the speakers were not going to play too much below 100Hz well. The tones would just not be low as compared to the rest of the movie. Remember too...the tones are on when the sound is on so you wouldn't hear them above the normal audio.