I didnt align the A chain, our tech did when he was up here last, I wasnt around at the time.

Josh

Conventional sibilance distortion is usually caused either by selective clipping of upper mid-range signals (harmonic distortion) which produces new higher frequency harmonics or by non-linear dynamic action which often occurs in compressor-limiters used in studios, resulting in excessive emphasis of low energy speech sounds like "s". This latter phenomenon is commonly referred to as "excessive sibilance" rather than sibilance distortion.

In optical film soundtracks the type of sibilance distorion caused by cross modulation distortion results in the generation of new lower frequency signals, not dissimilar to the effects of aliasing in analog to digital conversion. However the audible effect of these three types of sibilance distortion is noticeably different.

John, on the subject of cross modulation distortion, do you know what the "carrier" frequency is that is normally used for the cross modulation test signal used by labs? The article you provided a link to mentions that 400Hz is used as the amplitude modulating frequency but not what the higher "modulated" frequency is. I thought is was around the 4.5kHz mark.

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Ray Derrick
President/Chief Engineer
Panalogic Corporation Sydney, Australia
Phone: 61 (0)2 9894 6655 Fax: 61 (0)2 9894 6935

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The original SMPTE paper by Baker and Robinson suggested 9000 Hz and 400 Hz. as the frequencies:

J. O. Baker and D. H. Robinson, "Modulated High-Frequency Recording as a Means of Determining Conditions for Optimal Processing," Jour. SMPE, 30:3-17, January 1938

SMPTE Recommended Practice RP 104 states:

"3.1.2 Section 2: A high-frequency sinusoidal
signal amplitude modulated to (80 ± 5)% of full
modulation (2.0 dB ± 0.5 dB below full modula-tion)
at 400 Hz ± 10 Hz. The peak amplitude of
this modulated signal will be (80 ± 5)% of that
required for full modulation of the audio track (or
2.0 dB ± 0.5 dB below full modulation). The high
frequency will be 6000, 7000, 8000, or 9000 Hz
± 100 Hz for formats 16-mm and larger. The
modulation high frequency will be 4000 Hz ± 100
Hz for formats 8-mm and smaller."

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Also, thanks for the info John.

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Ray Derrick
President/Chief Engineer
Panalogic Corporation Sydney, Australia
Phone: 61 (0)2 9894 6655 Fax: 61 (0)2 9894 6935

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If memory serves me correctly, you were looking at the output of a microphone pre-amp, and I wonder if you were seeing a HF boost that was actually built into the pre-amp itself.

If you were looking at the output of the Cat 240, chances are the slit loss compensation adjustments are quite active.

Just my thoughts...

To get a response which is truly flat to 16kHz (after slit loss correction) reverse scan readers use a .0005" (.013mm) slit. Once again, this is the height of the slit which is effectively focused on the film, the slit on the surface of the solar cell can be as much as 3.5 times larger. This is because of the magnification of the lens.

------------------
Ray Derrick
President/Chief Engineer
Panalogic Corporation Sydney, Australia
Phone: 61 (0)2 9894 6655 Fax: 61 (0)2 9894 6935

From the diagram it can be seen that a null appears at the frequency whose wavelength is equal to the size of the slit (or head gap) and is repeated at multiples of that frequency. It is quite easy to calculate the wavelength (in inches) of any frequency on 24fps film by dividing 18 (18" per second) by the frequency in Hertz.