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Using Clock Source Creatively

July 3, 2009

Today I’ve had what I think is called a ‘happy accident’.

A scene from the film that I’m currently working on involves a building burning down while it’s occupants try to escape.  This was relatively straightforward to tracklay as I’ve already got a good selection of fire FX in my library.

When tracklaying a scene, I’ll play my FX against the dialogue on the left hand side of the guide track in order to make sure they’re not clashing.  On this occasion I noticed that the dialogue seemed pretty deep and slow.  I’m not that familiar with the actor’s voices yet but I was pretty sure that the cast couldn’t all sound like Barry White.  Due to the fact that I hadn’t knowingly changed any of the settings in my Pro Tools recently, the only thing I could guess was that a mistake had been made when the guide track was created.

However, after further investigation, I eventually realised that my clock reference had changed from it’s usual ‘Internal’ setting and was now referencing my minidisc player through it’s optical connection.  As a result, my 48k session was now playing back slow at 44.1.

Due to the fact that I’ve always just set it to ‘Internal’ in the past, I never realised or even considered the idea that setting the clock reference to a sample rate other than that of the session would have a corresponding effect on the speed of playback.  If pushed, I would have guessed it would cause glitching or no playback at all.

Most people seem to be aware that importing audio into a Pro Tools session at the wrong sample rate can provide better quality pitchshifting than if you shift the audio a similar amount using a plugin.  One of the reasons I now record at 96kHz whenever possible is so that I can get the best results should I want to bring it straight into a 48k session without converting it.

Sometimes though, 96 to 48 is too big a jump for anything other than extreme sound design.  When I listened to my ‘burning building’ FX at the correct speed, it wasn’t a massive difference but some of the bassier ‘inferno’ sounds had lost some of their warmth and low end.  Consequently, I’ve recorded these sounds digitally into my DAT machine at 44.1 then re-recorded them back into Pro Tools (analogue this time) with it’s clock reference reset to ‘Internal’, so that the session plays at the correct speed but retains the low end I could previously hear.  Obviously tweaking was needed in order to sync to picture again but this was relatively straightforward.

What’s more, I’m also able to set my DAT machine to 32kHz which, in theory, creates the option to audition sounds at another even slower speed if necessary.

Pitchshifting can be a little clichéd in sound design sometimes I think, and often I try to avoid it unless it serves a specific purpose.  However, pitchshifting using incorrect sample rates can produce really interesting results so I’m happy to have accidentally made a discovery that gives me more options when processing sounds in this way.

From → Post Production

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