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Gear / Technical Help => Post-Processing, Computer / Streaming / Internet Devices & Related Activity => Topic started by: beatkilla on September 06, 2010, 05:52:36 PM
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Im trying to understand why when i stretch audio that has no clipping to match up with video there is clipping after stretching just a tiny bit...stretching it to be maybe 2 seconds longer. Why does this happen?
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Stetching will involve resampling. Sometimes samples are interpolated outside the normal range if the signal is approaching a maximum value (or maximum negative value).
Erik de Castro Lopo explains this well in his FAQ regarding the libsamplerate API. http://www.mega-nerd.com/SRC/faq.html (http://www.mega-nerd.com/SRC/faq.html) (see Q1)
But if you are working in floating point in software it should not clip. If in fixed point (16/24 bit), try reducing the level a tiny bit.
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Although it probably seems like very little stretching, 2 seconds is a good amount and so the software youre using has to basically make up additional sample points along the new waveform where they hadnt existed before. also, when the softwares algorithms are crunching these numbers to resample, little clicks, pops, and other artifacts can surface as a result and that could be whats causing the audio to clip. even though you may not be able to hear them or see them at first glance, if youre able to zoom into the waveform all the way to sample level you may just find a nasty little peak. i know ive found similar issues as a result of using the 'time compression/expansion' tool in pro tools.
(this is my understanding anyways. i hope im not wrong.)
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Thanks to both of you.im using sony vegas pro 9.it has 32bit floating point video levels. Ill have to look into floating point audio.