Time Stretch And Pitch Change For Film Applications; Surround Post-Processing; Time Fit - Merging Pyramix User Manual

Algorithm
Time Scaling (also known as 'Time Stretching' , 'Time Compression/Expansion' and 'Time Correction') is the process
of changing the length of a sound or sounds without changing its pitch. When a sound is transposed by playing it
back at a different speed, e.g. when slowing down the playback speed of a tape recorder, it will play back at a dif-
ferent tempo but also at a different pitch. While this may be fine when tuning drum loops to match the speed of a
recording it will make pitched sounds - like vocals - sound totally out of tune. Therefore it is desirable to provide a
process that enables the duration and pitch of a recording to be changed independently from each other.

Time Stretch and Pitch Change for Film Applications

There are three main categories of Cinema time stretching and pitch changing requirements:
1) Conversion of audio rushes from 24 to 25 or 25 to 24 when their associated video or film has to be sped up or
slowed down. The main reasons are:
a. The shooting has been done with film AND video, so one part of the rushes or the other have to be sped up
or slowed down.
b. The telecine process to bring the film rushes to video for editing didn't preserve the original speed, intention-
ally or by mistake.
c. The shooting has been done on video at 25fps (intentionally or by mistake) and has to go to film.
Pyramix provides various solutions to this problem:
Batch conversion
of a whole media folder. Just select all media to stretch/squeeze / pitch change and select the menu Quick Con-
vert > Prosoniq MPEX4 module. All media will be processed in one shot. Media will have to be re-synchronized in
time with their video equivalent by using the reference "Clap".
In the case where all the media are already synchronized in time with their video equivalent (either manually or
because they've been properly stamped while recording), then simply send all these media to their original Time-
Code (time stamp) in a Pyramix project and select the menu item Project > Stretch / Pitch . All media will be prop-
erly stretched/squeezed and their position will be also correctly updated. The new original TimeCode (time stamp)
can then be written back to the media by selecting the menu item Clips > Operations > Update Media Original
TC , so these new media can now be used exactly as if they've been recorded and stamped at that new speed,
allowing also auto-conformation or other TimeCode based processes. All information stored in the Clips referenc-
ing these media in the Timeline (like fades, sync points, gain curve, ...) are also stretched/squeezed properly.
Optionally the media can be consolidated to convert only the required part
The two processes described above are necessary when a mix of different source material speed have to be "nor-
malized". In the case where it is known from the beginning that the whole editing and mix will have to be
stretched back to the other (original rushes) speed, Merging provides a very convenient solution in term of hard-
disk space, conversion time and finally sound quality. The Virtual Transport Video Player allows playing the video
editing at a different speed than the audio material allowing matching (for instance and in the majority of cases) a
video running at 24 frames per second with an audio editing stamped at 25 frames per seconds. This avoids com-
pressing the audio so it matches the video being played too fast (25fps instead of 24) but preferably run the video
at the correct speed (24fps) and therefore the audio also.

Surround Post-processing

Conversion of a final mix from 24 to 25 for DVD/Video distribution of a film or 25 to 24 for film distribution of a
video shot and edited movie.
Pyramix allows stretching/squeezing a whole surround mix by selecting the menu Project > Surround Post-pro-
cessing and choosing the Prosoniq MPEX4 24/25 Time Stretcher module. This function stretches/squeezes a
whole 5.1 mix without inter-channels phase artifacts thanks to the new Prosoniq MPEX4 algorithm. This function
allows processing multiple stem surround mixes stem by stem. Due to artefacts introduced by most time stretch-
ing algorithms available until now, the normal procedure was to separate the dialogue stem and the music/
effects/ambiance stems, time-stretch them separately and remix them afterward. Although the Surround Post-
processing function allows this methodology, this is no longer required due to the very high quality of the MPEX4
module. Therefore a complete mix can be stretched in one pass retaining maximum sound quality.

Time fit

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