---
name: "stretch"
section: "1"
platform: "linux"
package: "pvoc"
version: "0.1.12-6"
release: "Arch Linux 2026-11-01"
platforms: ["linux"]
url: "https://new.carta.tech/stretch"
---

# stretch(1)

time stretching tool for sound data

## NAME

stretch - time stretching tool for sound data

## SYNOPSIS

**stretch \[***options***\] \[***input* **\[***output***\]\]**

## DESCRIPTION

**The stretch utility allows you to lengthen or shorten the duration** **of an audio data stream without affecting the pitch of the sampled** **data. It employs phase-vocoding to achieve the effect,** **usually leading to better results than time-domain techniques.** **Input audio data can be composed of multiple channels, in** **which case output also is.**

**Both** *output* **and** *input* **can be '-', indicating that signal** **data is to be read from** *stdin* **or written to** *stdout*  **respectively (You can also omit the file names for the same effect,** **starting with** *output***). In either case, the sample format is signed** **16-bit little-endian (aka CD format).**

**For physical file access, the utility makes use of the** *sndfile* **library. The tool tries to guess the intended output file format from** **the filename extension; in addition, you can specify the output bit depth** **(quantization) with the -b (--bits) parameter.**

**The tool** **is not capable of directly replacing the contents of the input file.**

## OPTIONS

**The simplest invocation of the tool is:**

	**stretch -t 1.5 infile.wav outfile.wav**\

**This example stretches** *infile.wav* **to** **150 % duration and writes the result to** *outfile.wav***.**

### Most useful options:

- *-t, --times* **\<stretch factor\>**

  **sets the ratio by which the duration of the sound signal is scaled.** **Extreme values can cause audible artefacts in the output signal,** **usually perceived as cyclic amplitude modulation. To achieve an** **exact time expansion/compression ratio, the product of this**  **and the -o (--overlap) parameter needs to be an integer** **value.**

- *-a, --amplify* **\<factor\>**

  **sets the linear amplification factor for the output signal.** **The default value is 1.0 .**

- *-q, --quiet*

  **makes the utility be silent about what it does.**

### Processing control options:

- *-f, --fft* **\<DFT length\>**

  **sets the length of the DFT (discrete Fourier transform), which should** **be a power of two for best results. Odd values may cause the utility** **to throw up. Larger DFT sizes imply better frequency resolution at the** **cost of increased computational demand. The default value is 1024 samples.**

- *-o, --overlap* **\<overlap\>**

  **controls the interval at which recomposition of the signal takes** **place. Smaller values imply a smoother** **result in exchange for increased computational demand.** **The default value is 128 samples.**

### Piped input signal options:

**If signal input is from** *stdin***, the default assumption about the** **data format (other than the aforementioned 16-bit signed little-endian** **convention) is two-channel audio at 44.1 kHz sample rate. The following** **options override these:**

- *-c, --channels* **\<channel count\>**

  **no surprises: 1 is mono, 2 stereo etc.**

- *-r, --rate* **\<sample rate\>**

  **sets the sample rate.**

### Output bit depth:

- *-b, --bits* **\<quantization\>**

  **sets the output bit depth (only for physical file output).** **8, 16 or 24 for signed integers, 32 or 64 for floating point.** **The default is 16-bit. (Internal precision is 32 bit floating-point.)**

- *-l, --limit*

  **this option causes the utility to clip the output signal to stay** **within the output quantization** **or the \[-1,+1\] range if output is in floating-point format.** **The use of this flag is highly recommended when output is in integer** **sample format (--bits less than 32 or** *stdout* **output).**

### Information options:

- *-h, --help*

  **prints version information and a list of supported file formats/extensions,** **then quits.**

- *-v, --version*

  **prints version information, then quits.**

## EXAMPLES

**A few example invocations of the utility, all assuming source data** **is in CD format (signed 16-bit samples, stereo, 44.1 kHz):**

- **stretch -o 100 -t 1.2 cdda.wav \| aplay -fcd**

  **stretches** *cdda.wav* **to exactly 120 %, piping the output to the**  *aplay* **program for immediate playback.**

- **cat file.ogg \| oggdec - \| stretch -t.8 \| aplay -fcd**

  **plays back an** *ogg* **stream, accelerated to 80 % duration.  If** **you prefer** *mp3***, an equivalent incantation is:**

- **madplay -o raw:- file.mp3 \| stretch -t.8 \| aplay -f cd**

  ## BUGS

**Lousy command line parsing and error feedback.**  **Lots of combinations of output file formats**  **and quantization untested,** **as is the operation on big-endian systems.** **Phase vocoding chews a lot of CPU cycles.**

## AUTHORS

**The original** **phase vocoder implementation was done by Mark Dolson at UCSD, part** **of the CARL suite, skillfully converted to streaming operation** **by Richard Dobson.**

**The stretch tool and this manual page were written by Tim Goetze**  **\<tim@quitte.de\>.**

## HOMEPAGE

**The latest version of this tool can be obtained from** *http://quitte.de/dsp/pvoc.html* **.**