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I have some low quality audio from my native tongue on a VHS. I am using this audio to dub HQ released of the same program (from another language source). The video frames/second ratio is 25:23.98 . I do not want to tamper with the fps ratio, since I am still using the other audio tracks as alternative languages in my video.

I can't notice a pitch difference from this conversion, I can only hear the pitch-changing VHS artefacts.

Is a 25/23.98 ratio enough to need pitch correction? What is the rule of thumb? Would the VHS artefacts hide the pitch difference (too much pitch-noise to actually matter) or would the average pitch difference drive an audiophile up the wall?

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The difference between 25fps and 23.98fps is about 72% of a semitone. I can think of two effects this difference might have.

If there is any music in the clip, then the notes will no longer be aligned to any "true" notes in an A=440 scale. People with a finely honed sense of pitch (like me) will definitely notice this. It will be annoying to many of us. Not quite "drive us up the wall" annoying, but certainly enough to capture our attention and be distracting.

For any speech in the clip, the formant frequencies will be slightly changed, which will modify the vowel sounds slightly. A native speaker of the language of the speech probably won't notice. But for someone whose native language is different from the language in the clip, some of the vowels may take a fraction of a second longer to identify correctly, or may be mistaken for different vowels. This will make it slightly harder for them to understand some of the speech.

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  • $\begingroup$ Thanks for sharing. You have convinced me to add pitch correction to my code. $\endgroup$ – Simon Streicher Jan 11 '15 at 8:39
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Audiophiles don't hear anything unless they are told what to expect.

Joke aside, this is equivalent to transposition by a bit less than a semitone. The effect won't be noticed on voices - this is way too low for any kind "chipmunk" effect to be observed. As for music, some people very familiar with the original music might detect the change of tonality and/or tempo. But such stretching ratios are not unusual at all - DJs doing beat-matching, TV channels speeding up a sitcom to squeeze in more ads, and many, many movie to video conversions (telecine) have routinely used it.

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