Re: FLASH: flash audio

[Nigel Randsley-Pena]

Dave,


Well this took some time to answer because I decided to conduct a series

of tests on Flash audio.

First of all I started out with a series of 2 second clips of a sine at

440Hz with settings of 11025 22050 and 44100 at 8 and 16bit all

mono.These were all normalised using average RMS to -16dB.

Importing these into flash and playing them direct from the library

gives these results :

44100 8 and 16 bit - Clean, no hiss no clipping

22050 16bit - Clean no hiss no clipping

22050 8bit - Clean with acceptable hiss, no clipping

11025 16 and 8 bit - Clipping occurs. Some hiss.

Using the 22050 16bit version to test export the lowest acceptable

setting was 11025kHz 4Bit resulting in an 8:1 compression ratio.

Next I generated a series of 2 second clips of sine waves at frequencies

from 50 to 11000Hz at 150Hz intervals, all normalised to -6dB in 22050

16bit format.

These were used to test export settings in flash audio.

Translating the conclusions into pratical results gives the following

recommendations :

The default export settings should be used for general purpose sound

clips. These can be lowered for low frequency short clips (<.5sec).

Higher frequencies compress badly sometimes forcing the use of 22050

5bit settings for acceptable results.

The compression engine apparently uses a truncating method so clipping

will occur with some ease.

For online use input files settings should be at 22050 16bit mono, use

44100 16bit only for offline movies.

Stereo effects are best obtained with the sound settings inside flash

and not with stereo files.

Frequencies above 9000Hz will tend to give strange results so try to

keep away from them.


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