The Scale command rescales audio data, producing a new audio object with the specified size.

The audArray parameter specifies the audio to scale, and must be a dense, rectangular, one or two dimensional Array, Vector, or Matrix with datatype=float[8].

The scale parameter specifies either the desired scaling ratio, or the desired length, in samples, of the scaled audio data. The former is expressed as a numeric value. The latter is expressed as an integer range giving the desired resulting array indices.

By default, scaling is done using B-spline interpolation.  This produces excellent results reasonably fast. When reducing audio data using scale factors smaller than 1/2.5, the scaling is done in steps to avoid unnecessary information loss. For example, scaling by 1/4 is accomplished by scaling twice by 1/2. The nature of the algorithm makes this stepwise scaling unnecessary when enlarging audio data.

If the method=nearest option is specified, scaling is done using the nearest-neighbor algorithm. This produces poorer results, but the algorithm is very fast.  This method is often suitable for producing low-quality rescalings of audio data.

Specifying method=bspline is equivalent to the default behavior.

NOTE: Scaling does not change the sampling rate of the data, which means that it does change the pitch. For example, scaling down by a factor of 0.5 will double the pitch (increase it by one octave). To resample audio data without affecting the pitch, use the AudioTools[Resample] command.

$\mathrm{audiofile}≔\mathrm{cat}\left(\mathrm{kernelopts}\left(\mathrm{datadir}\right)\,''/audio/stereo.wav''\right)\:$

$\mathrm{with}\left(\mathrm{AudioTools}\right)\:$

$\mathrm{aud}≔\mathrm{Read}\left(\mathrm{audiofile}\right)$

$\mathrm{aud}≔\left[\begin{array}{cc}''Sample\; Rate''& 22050\\ ''File\; Format''& \mathrm{PCM}\\ ''File\; Bit\; Depth''& 8\\ ''Channels''& 2\\ ''Samples/Channel''& 19962\\ ''Duration''& 0.90531s\end{array}\right]$

$\mathrm{small}≔\mathrm{Scale}\left(\mathrm{aud}\,1..5000\right)$

$\mathrm{small}≔\left[\begin{array}{cc}''Sample\; Rate''& 22050\\ ''File\; Format''& \mathrm{PCM}\\ ''File\; Bit\; Depth''& 8\\ ''Channels''& 2\\ ''Samples/Channel''& 5000\\ ''Duration''& 0.22676s\end{array}\right]$

$\mathrm{squished}≔\mathrm{Scale}\left(\mathrm{aud}\,0.25\right)$

$\mathrm{squished}≔\left[\begin{array}{cc}''Sample\; Rate''& 22050\\ ''File\; Format''& \mathrm{PCM}\\ ''File\; Bit\; Depth''& 8\\ ''Channels''& 2\\ ''Samples/Channel''& 4991\\ ''Duration''& 0.22635s\end{array}\right]$

$\mathrm{quick}≔\mathrm{Scale}\left(\mathrm{aud}\,0.25\,\mathrm{method}=\mathrm{nearest}\right)$

$\mathrm{quick}≔\left[\begin{array}{cc}''Sample\; Rate''& 22050\\ ''File\; Format''& \mathrm{PCM}\\ ''File\; Bit\; Depth''& 8\\ ''Channels''& 2\\ ''Samples/Channel''& 4991\\ ''Duration''& 0.22635s\end{array}\right]$