Vern Dias
Second Unit
- Joined
- Apr 27, 1999
- Messages
- 353
- Real Name
- Theodore V Dias
I am not sure that everyone here understands exactly how Perspectasound works.
You start with one audio channel (mono), filter any content below 50 Hz (to avoid any interacttion with the keying frequencies), and mix it with 3 subaudible (only if the theatre strictly complies with academy curve) tones.
I've heard Perspecta prints played in certain (non Perspecta equipped) theatres that did not use the academy bass rolloff where you could clearly hear the constant rumble throughout the entire film.
The tones (30Hz, 35Hz, & 40Hz) are mixed in with the mono audio at varying levels corresponding to the desired gain to be applied to each (L, C, R) channel. IOW, the higher the level of the specific tone, the higher the level from the corresponding channel.
It's the responsibility of the Perspectasound integrator unit in the booth to respond to the level of each specific frequency tone and alter the gain of each channel based on the level of each tone.
None of this changes the fact that it is an optical track with its inherently limited high frequency response (maybe 6K on a good day using a perfectly adjusted sound head with no oil contamination on the scanning lens) and a limited low frequency range (50 Hz mandated by the fact that the control tones have to be filtered to avoid being audible in the auditorium).
With all these compromises, I'll take a BD audio track remastered from the stems any day. I suppose that if the studio had access to a mag element with the encoded tones, you could avoid the HF loss, but I'm pretty sure there is no way way around the 50 Hz restriction.
So, while having a Perspecta track included could be interesting for historical purposes, I doubt it would be the track an audiophile would choose in order to hear the highest quality audio.
Oh, yeah, I'm pretty sure that the White Christmas BD is stereo, not re-channeled mono. (But I'll have a listen later today to double check.) I was wrong, not sure where it sourced from.
Just my $.02 YMMV
You start with one audio channel (mono), filter any content below 50 Hz (to avoid any interacttion with the keying frequencies), and mix it with 3 subaudible (only if the theatre strictly complies with academy curve) tones.
I've heard Perspecta prints played in certain (non Perspecta equipped) theatres that did not use the academy bass rolloff where you could clearly hear the constant rumble throughout the entire film.
The tones (30Hz, 35Hz, & 40Hz) are mixed in with the mono audio at varying levels corresponding to the desired gain to be applied to each (L, C, R) channel. IOW, the higher the level of the specific tone, the higher the level from the corresponding channel.
It's the responsibility of the Perspectasound integrator unit in the booth to respond to the level of each specific frequency tone and alter the gain of each channel based on the level of each tone.
None of this changes the fact that it is an optical track with its inherently limited high frequency response (maybe 6K on a good day using a perfectly adjusted sound head with no oil contamination on the scanning lens) and a limited low frequency range (50 Hz mandated by the fact that the control tones have to be filtered to avoid being audible in the auditorium).
With all these compromises, I'll take a BD audio track remastered from the stems any day. I suppose that if the studio had access to a mag element with the encoded tones, you could avoid the HF loss, but I'm pretty sure there is no way way around the 50 Hz restriction.
So, while having a Perspecta track included could be interesting for historical purposes, I doubt it would be the track an audiophile would choose in order to hear the highest quality audio.
Just my $.02 YMMV
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