Effects and Plug-Ins : Flux
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Prosoniq
MPEX4 Timestretch and pitch change
Overview
The MPEX4 algorithm for Pyramix has been developed with the German based company Prosoniq, well known for
their high quality digital audio algorithms.
MPEX stands for Minimum Perceived Loss Time Compression/EXpansion. Incorporating this technology into Pyra-
mix Virtual Studio enables users to adjust timing and pitch of existing material with outstanding results and ease
of use.
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-
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