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Sound Characteristics - fractional sample rates

 
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sthompson



Joined: 01 Apr 2009
Posts: 1

PostPosted: Wed Apr 01, 2009 6:55 pm    Post subject: Sound Characteristics - fractional sample rates Reply with quote

Martin,

I have been using Amadeus for quite some time now and love it. It performs one feature that no other editor that I have found can do - or it used to.

I mix feature films and often times I must very precisely modify the length of a long file to match the sample length of another file (this prevents phase errors that can throw off surround decoders and the like). To do this, I have been using Amadeus Pro 1.0's batch mode to modify the sound characteristics in the following manner:

1. Change the sample rate WITHOUT resampling the audio to some fractional sample rate. i.e. 48000 -> 47952.56
2. Change the sample rate back to the working sample rate WITH resampling. i.e. 47952.56 -> 48000

It may seem insignificant, but by calculating the desired sample length of a clip of audio and the current one and taking that ratio, I can get very precise clip length (albeit with the pitch change - but that is acceptable) and this can make a big difference on a long clip such as a complete feature film of 2+ hours.

I believe this is possible (only a guess) with Amadeus Pro because AP works in its own file format and is not limited to integer sample numbers like WAV and AIF are (before AP I could do the same thing by modifying the resource fork of SD2 files - but that's another story). In the end, I am sample rate converting back to WAV at 48000 Hz for use in Pro Tools.

Pro Tools works natively in BWAV or AIF and this will not support this level of precision.

Recently I have transitioned to Leopard and have been forced to upgrade to AP 1.4. Unfortunately, versions of AP after 1.0 return an error "Fell Short of Minimum" when entering a fractional value under Sound Characteristics. I figured that AP had been updated and would not support this type of precision anymore, however I recently discovered that, if I used a batch file that was created with Amadeus 1.0 with 1.4, it indeed would work as expected and give me the proper number of samples in my clip as calculated with the fractional sample rate.

Unfortunately, I have no way to edit the batch file and the current version of AP will not allow me to enter values with the precision I need.

I know this may seem like an esoteric need, but AP has been the core of my workflow in this regard for some time and I am a bit in a quandry. I'm not sure how your calculations work, but if you test it in 1.0 and enter, for example, 47952.5, 47952.6, 47952.7 as mentioned and then resample back to 48kHz you will see that the result is files of different sample counts as I describe. It really makes a huge difference when working with big files. Even Pro Tools' own PAL-NTSC conversion method is several frames out over the length of a feature film due to it's inability to precisely match the conversion ratio.

Is there anything you can do to help? It appears that the limit in the Sound Characteristics window is simply an interface one and not a limitation on the calculation itself, given that the old batch files work correctly.

Thanks,

Steve Thompson
Technical Director
POP Sound
Santa Monica, CA USA
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Martin Hairer
Site Admin


Joined: 08 Nov 2006
Posts: 1616

PostPosted: Thu Apr 02, 2009 6:06 pm    Post subject: Sound Characteristics - fractional sample rates Reply with quote

Quote:
Pro Tools works natively in BWAV or AIF and this will not support
this level of precision.

I don't think it has to do with this, since AIFF stores sampling rates
as 80-bit floating points, which provides much much more precision
than you'll ever need. It's probably more of a matter of rounding off
the values taken from the user interface for the purpose of displaying
them "nicely"...

Quote:
Recently I have transitioned to Leopard and have been forced to
upgrade to AP 1.4. Unfortunately, versions of AP after 1.0 return an
error "Fell Short of Minimum" when entering a fractional value under
Sound Characteristics. I figured that AP had been updated and would
not support this type of precision anymore, however I recently
discovered that, if I used a batch file that was created with
Amadeus 1.0 with 1.4, it indeed would work as expected and give me
the proper number of samples in my clip as calculated with the
fractional sample rate.

Unfortunately, I have no way to edit the batch file and the current
version of AP will not allow me to enter values with the precision I
need.

You are right, this is a user interface bug. I'll fix that for version
1.4.1. Regards,

Martin

HairerSoft
http://www.hairersoft.com/


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