AIFF and AIFC files

Ways for storing a Sound object on disk.

File format

Reading

Read from file... recognizes AIFF and AIFC files with 8-bit and 16-bit encoding, but not compressed AIFC files. It recognizes any sampling frequency. The two channels of stereo files are averaged. Read two Sounds from AIFF file... reads both channels separately and names them left and right.

The sample values are divided by 2(numberOfBitsPerSample – 1), so that the amplitude of the resulting Sound is between –1.0 and +1.0; the maximum sound pressure level for a sine wave is therefore: 20 · 10log (√2 / 2·10–5) = 91 dB.

The resulting Sound will appear in the List of Objects; its name will be equal to the file name, without extension.

Saving

With Save as AIFF file....

The samples of the Sound are multiplied by 32768 and quantized between –32768 and 32767.

To avoid clipping, keep the absolute amplitude below 1.000. If the maximum sound pressure level is 91 dB (top = 32767), the quantization threshold is (top = 1/2) –5 dB.


© ppgb, January 31, 2011