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SoundTouch library compiled for iOS

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SoundTouch audio processing library v1.8.0

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SoundTouch library Copyright Olli Parviainen 2001-2014

1. Introduction

SoundTouch is an open-source audio processing library that allows changing the sound tempo, pitch and playback rate parameters independently from each other, i.e.:

  • Sound tempo can be increased or decreased while maintaining the original pitch
  • Sound pitch can be increased or decreased while maintaining the original tempo
  • Change playback rate that affects both tempo and pitch at the same time
  • Choose any combination of tempo/pitch/rate

1.1 Contact information

Author email: oparviai 'at'

SoundTouch WWW page:

2. Compiling SoundTouch

Before compiling, notice that you can choose the sample data format if it's desirable to use floating point sample data instead of 16bit integers. See section "sample data format" for more information.

2.1. Building in Microsoft Windows

Project files for Microsoft Visual C++ are supplied with the source code package. Go to Microsoft WWW page to download Microsoft Visual Studio Express version for free.

To build the binaries with Visual C++ compiler, either run "make-win.bat" script, or open the appropriate project files in source code directories with Visual Studio. The final executable will appear under the "SoundTouch\bin" directory. If using the Visual Studio IDE instead of the make-win.bat script, directories bin and lib may need to be created manually to the SoundTouch package root for the final executables. The make-win.bat script creates these directories automatically.

2.2. Building in Gnu platforms

The SoundTouch library compiles in practically any platform supporting GNU compiler (GCC) tools. SoundTouch requires GCC version 4.3 or later.

To build and install the binaries, run the following commands in /soundtouch directory:


./bootstrap  -

| Creates "configure" file with local autoconf/automake toolset. | |

./configure  -


Configures the SoundTouch package for the local environment. Notice that "configure" file is not available before running the "./bootstrap" command as above.

| |

make         -


Builds the SoundTouch library & SoundStretch utility.

| |

make install -


Installs the SoundTouch & BPM libraries to /usr/local/lib and SoundStretch utility to /usr/local/bin. Please notice that 'root' privileges may be required to install the binaries to the destination locations.


2.2.1 Required GNU tools 

Bash shell, GNU C++ compiler, libtool, autoconf and automake tools are required for compiling the SoundTouch library. These are usually included with the GNU/Linux distribution, but if not, install these packages first. For example, Ubuntu Linux can acquire and install these with the following command:

**sudo apt-get install automake autoconf libtool build-essential**

2.2.2 Problems with GCC compiler compatibility

At the release time the SoundTouch package has been tested to compile in GNU/Linux platform. However, If you have problems getting the SoundTouch library compiled, try disabling optimizations that are specific for x86 processors by running ./configure script with switch


Alternatively, if you don't use GNU Configure system, edit file "include/STTypes.h" directly and remove the following definition:


2.2.3 Compiling Shared Library / DLL version

The GNU compilation does not automatically create a shared-library version of SoundTouch (.so or .dll). If such is desired, then you can create it as follows after running the usual compilation:

g++ -shared -static -DDLL_EXPORTS -I../../include -o SoundTouch.dll \
     SoundTouchDLL.cpp ../SoundTouch/.libs/libSoundTouch.a
sstrip SoundTouch.dll

2.1. Building in Android

Android compilation instructions are within the source code package, see file "source/Android-lib/README-SoundTouch-Android.html" in the package.

3. About implementation & Usage tips

3.1. Supported sample data formats

The sample data format can be chosen between 16bit signed integer and 32bit floating point values, the default is 32bit floating point.

In Windows environment, the sample data format is chosen in file "STTypes.h" by choosing one of the following defines:

  • #define SOUNDTOUCHINTEGERSAMPLES for 16bit signed integer
  • #define SOUNDTOUCHFLOATSAMPLES for 32bit floating point

In GNU environment, the floating sample format is used by default, but integer sample format can be chosen by giving the following switch to the configure script:

./configure --enable-integer-samples

The sample data can have either single (mono) or double (stereo) audio channel. Stereo data is interleaved so that every other data value is for left channel and every second for right channel. Notice that while it'd be possible in theory to process stereo sound as two separate mono channels, this isn't recommended because processing the channels separately would result in losing the phase coherency between the channels, which consequently would ruin the stereo effect.

Sample rates between 8000-48000H are supported.

3.2. Processing latency

The processing and latency constraints of the SoundTouch library are:

  • Input/output processing latency for the SoundTouch processor is around 100 ms. This is when time-stretching is used. If the rate transposing effect alone is used, the latency requirement is much shorter, see section 'About algorithms'.
  • Processing CD-quality sound (16bit stereo sound with 44100H sample rate) in real-time or faster is possible starting from processors equivalent to Intel Pentium 133Mh or better, if using the "quick" processing algorithm. If not using the "quick" mode or if floating point sample data are being used, several times more CPU power is typically required.

3.3. About algorithms

SoundTouch provides three seemingly independent effects: tempo, pitch and playback rate control. These three controls are implemented as combination of two primary effects, sample rate transposing and time-stretching.

Sample rate transposing affects both the audio stream duration and pitch. It's implemented simply by converting the original audio sample stream to the  desired duration by interpolating from the original audio samples. In SoundTouch, linear interpolation with anti-alias filtering is used. Theoretically a higher-order interpolation provide better result than 1st order linear interpolation, but in audio application linear interpolation together with anti-alias filtering performs subjectively about as well as higher-order filtering would.

Time-stretching means changing the audio stream duration without affecting it's pitch. SoundTouch uses WSOLA-like time-stretching routines that operate in the time domain. Compared to sample rate transposing, time-stretching is a much heavier operation and also requires a longer processing "window" of sound samples used by the processing algorithm, thus increasing the algorithm input/output latency. Typical i/o latency for the SoundTouch time-stretch algorithm is around 100 ms.

Sample rate transposing and time-stretching are then used together to produce the tempo, pitch and rate controls:

  • 'Tempo' control is implemented purely by time-stretching.
  • 'Rate' control is implemented purely by sample rate transposing.
  • 'Pitch' control is implemented as a combination of time-stretching and sample rate transposing. For example, to increase pitch the audio stream is first time-stretched to longer duration (without affecting pitch) and then transposed back to original duration by sample rate transposing, which simultaneously reduces duration and increases pitch. The result is original duration but increased pitch.

3.4 Tuning the algorithm parameters

The time-stretch algorithm has few parameters that can be tuned to optimize sound quality for certain application. The current default parameters have been chosen by iterative if-then analysis (read: "trial and error") to obtain best subjective sound quality in pop/rock music processing, but in applications processing different kind of sound the default parameter set may result into a sub-optimal result.

The time-stretch algorithm default parameter values are set by the following #defines in file "TDStretch.h":

#define DEFAULT_OVERLAP_MS      8

These parameters affect to the time-stretch algorithm as follows:

  • DEFAULTSEQUENCEMS: This is the default length of a single processing sequence in milliseconds which determines the how the original sound is chopped in the time-stretch algorithm. Larger values mean fewer sequences are used in processing. In principle a larger value sounds better when slowing down the tempo, but worse when increasing the tempo and vice versa. 

    By default, this setting value is calculated automatically according to tempo value.

  • DEFAULTSEEKWINDOWMS: The seeking window default length in milliseconds is for the algorithm that seeks the best possible overlapping location. This determines from how wide a sample "window" the algorithm can use to find an optimal mixing location when the sound sequences are to be linked back together. 

    The bigger this window setting is, the higher the possibility to find a better mixing position becomes, but at the same time large values may cause a "drifting" sound artifact because neighboring sequences can be chosen at more uneven intervals. If there's a disturbing artifact that sounds as if a constant frequency was drifting around, try reducing this setting.

    By default, this setting value is calculated automatically according to tempo value.

  • DEFAULTOVERLAPMS: Overlap length in milliseconds. When the sound sequences are mixed back together to form again a continuous sound stream, this parameter defines how much the ends of the consecutive sequences will overlap with each other.

    This shouldn't be that critical parameter. If you reduce the DEFAULTSEQUENCEMS setting by a large amount, you might wish to try a smaller value on this.

Notice that these parameters can also be set during execution time with functions "TDStretch::setParameters()" and "SoundTouch::setSetting()".

The table below summaries how the parameters can be adjusted for different applications:

| Parameter name | Default value magnitude | Larger value affects... | Smaller value affects... | Effect to CPU burden | |


| Default value is relatively large, chosen for slowing down music tempo | Larger value is usually better for slowing down tempo. Growing the value decelerates the "echoing" artifact when slowing down the tempo. | Smaller value might be better for speeding up tempo. Reducing the value accelerates the "echoing" artifact when slowing down the tempo | Increasing the parameter value reduces computation burden | |


| Default value is relatively large, chosen for slowing down music tempo | Larger value eases finding a good mixing position, but may cause a "drifting" artifact | Smaller reduce possibility to find a good mixing position, but reduce the "drifting" artifact. | Increasing the parameter value increases computation burden | |


| Default value is relatively large, chosen to suit with above parameters. | If you reduce the "sequence ms" setting, you might wish to try a smaller value. | Increasing the parameter value increases computation burden |

3.5 Performance Optimizations

General optimizations:

The time-stretch routine has a 'quick' mode that substantially speeds up the algorithm but may degrade the sound quality by a small amount. This mode is activated by calling SoundTouch::setSetting() function with parameter  id of SETTINGUSEQUICKSEEK and value "1", i.e.


CPU-specific optimizations:

  • Intel MMX optimized routines are used with compatible CPUs when 16bit integer sample type is used. MMX optimizations are available both in Win32 and Gnu/x86 platforms. Compatible processors are Intel PentiumMMX and later; AMD K6-2, Athlon and later.
  • Intel SSE optimized routines are used with compatible CPUs when floating point sample type is used. SSE optimizations are currently implemented for Win32 platform only. Processors compatible with SSE extension are Intel processors starting from Pentium-III, and AMD processors starting from Athlon XP.
  • AMD 3DNow! optimized routines are used with compatible CPUs when floating point sample type is used, but SSE extension isn't supported . 3DNow! optimizations are currently implemented for Win32 platform only. These optimizations are used in AMD K6-2 and Athlon (classic) CPU's; better performing SSE routines are used with AMD processor starting from Athlon XP.

4. SoundStretch audio processing utility

SoundStretch audio processing utility Copyright (c) Olli Parviainen 2002-2012

SoundStretch is a simple command-line application that can change tempo, pitch and playback rates of WAV sound files. This program is intended primarily to demonstrate how the "SoundTouch" library can be used to process sound in your own program, but it can as well be used for processing sound files.

4.1. SoundStretch Usage Instructions

SoundStretch Usage syntax:

soundstretch infilename outfilename [switches]




| Name of the input sound data file (in .WAV audio file format). Give "stdin" as filename to use standard input pipe. | |


| Name of the output sound file where the resulting sound is saved (in .WAV audio file format). This parameter may be omitted if you  don't want to save the output (e.g. when only calculating BPM rate with '-bpm' switch). Give "stdout" as filename to use standard output pipe. | |


| Are one or more control switches. |

Available control switches are:



| Change the sound tempo by n percents (n = -95.0 .. +5000.0 %) | |


| Change the sound pitch by n semitones (n = -60.0 .. + 60.0 semitones) | |


| Change the sound playback rate by n percents (n = -95.0 .. +5000.0 %) | |


| Detect the Beats-Per-Minute (BPM) rate of the sound and adjust the tempo to meet 'n' BPMs. When this switch is applied, the "-tempo" switch is ignored. If "=n" is omitted, i.e. switch "-bpm" is used alone, then the BPM rate is estimated and displayed, but tempo not adjusted according to the BPM value. | |


| Use quicker tempo change algorithm. Gains speed but loses sound quality. | |


| Don't use anti-alias filtering in sample rate transposing. Gains speed but loses sound quality. | |


| Displays the program license text (LGPL) |


  • To use standard input/output pipes for processing, give "stdin" and "stdout" as input/output filenames correspondingly. The standard input/output pipes will still carry the audio data in .wav audio file format.
  • The numerical switches allow both integer (e.g. "-tempo=123") and decimal (e.g. "-tempo=123.45") numbers.
  • The "-naa" and/or "-quick" switches can be used to reduce CPU usage while compromising some sound quality
  • The BPM detection algorithm works by detecting repeating bass or drum patterns at low frequencies of <250Hz. A lower-than-expected BPM figure may be reported for music with uneven or complex bass patterns.

4.2. SoundStretch usage examples

Example 1

The following command increases tempo of the sound file "originalfile.wav" by 12.5% and stores result to file "destinationfile.wav":

soundstretch originalfile.wav destinationfile.wav -tempo=12.5

Example 2

The following command decreases the sound pitch (key) of the sound file "orig.wav" by two semitones and stores the result to file "dest.wav":

soundstretch orig.wav dest.wav -pitch=-2

Example 3

The following command processes the file "orig.wav" by decreasing the sound tempo by 25.3% and increasing the sound pitch (key) by 1.5 semitones. Resulting .wav audio data is directed to standard output pipe:

soundstretch orig.wav stdout -tempo=-25.3 -pitch=1.5

Example 4

The following command detects the BPM rate of the file "orig.wav" and adjusts the tempo to match 100 beats per minute. Result is stored to file "dest.wav":

soundstretch orig.wav dest.wav -bpm=100

Example 5

The following command reads .wav sound data from standard input pipe and estimates the BPM rate:

soundstretch stdin -bpm

5. Change History

5.1. SoundTouch library Change History


  • Added support for multi-channel audio processing
  • Added support for cubic and shannon interpolation for rate and pitch shift effects besides the original linear interpolation, to reduce aliasing at high frequencies due to interpolation. Cubic interpolation is used as default for floating point processing, and linear interpolation for integer processing.
  • Fixed bug in anti-alias filtering that limited stop-band attenuation to -10 dB instead of <-50dB, and increased filter length from 32 to 64 taps to further reduce aliasing due to frequency folding.
  • Performance improvements in cross-correlation algorithm
  • Other bug and compatibility fixes


  • Added files for Android compilation


  • Sound quality improvements/li>
  • Improved flush() to adjust output sound stream duration to match better with ideal duration
  • Rewrote x86 cpu feature check to resolve compatibility problems
  • Configure script automatically checks if CPU supports mmx & sse compatibility for GNU platform, and the script support now "--enable-x86-optimizations" switch to allow disabling x86-specific optimizations.
  • Revised #define conditions for 32bit/64bit compatibility
  • gnu autoconf/automake script compatibility fixes
  • Tuned beat-per-minute detection algorithm


  • Added automatic cutoff threshold adaptation to beat detection routine to better adapt BPM calculation to different types of music
  • Retired 3DNow! optimization support as 3DNow! is nowadays obsoleted and assembler code is nuisance to maintain
  • Retired "configure" file from source code package due to autoconf/automake versio conflicts, so that it is from now on to be generated by invoking "boostrap" script that uses locally available toolchain version for generating the "configure" file
  • Resolved namespace/label naming conflicts with other libraries by replacing global labels such as INTEGERSAMPLES with more specific SOUNDTOUCHINTEGER_SAMPLES etc.

  • Updated windows build scripts & project files for Visual Studio 2008 support

  • Updated SoundTouch.dll API for .NET compatibility

  • Added API for querying nominal processing input & output sample batch sizes


  • Added normalization to correlation calculation and improvement automatic seek/sequence parameter calculation to improve sound quality
  • Bugfixes: 
    • Fixed negative array indexing in quick seek algorithm
    • FIR autoalias filter running too far in processing buffer
    • Check against zero sample count in rate transposing
    • Fix for x86-64 support: Removed pop/push instructions from the cpu detection algorithm. 
    • Check against empty buffers in FIFOSampleBuffer
    • Other minor fixes & code cleanup
  • Fixes in compilation scripts for non-Intel platforms
  • Added Dynamic-Link-Library (DLL) version of SoundTouch library build, provided with Delphi/Pascal wrapper for calling the dll routines
  • Added #define PREVENTCLICKATRATECROSSOVER that prevents a click artifact when crossing the nominal pitch from either positive to negative side or vice versa


  • Fixed a buffer overflow bug in BPM detect algorithm routines if processing more than 2048 samples at one call 


  • Improved sound quality by automatic calculation of time stretch algorithm processing parameters according to tempo setting
  • Moved BPM detection routines from SoundStretch application into SoundTouch library
  • Bugfixes: Usage of uninitialied variables, GNU build scripts, compiler errors due to 'const' keyword mismatch.
  • Source code cleanup


  • Changed static class declaration to GCC 4.x compiler compatible syntax.
  • Enabled MMX/SSE-optimized routines also for GCC compilers. Earlier the MMX/SSE-optimized routines were written in compiler-specific inline assembler, now these routines are migrated to use compiler intrinsic syntax which allows compiling the same MMX/SSE-optimized source code with both Visual C++ and GCC compilers.
  • Set floating point as the default sample format and added switch to the GNU configure script for selecting the other sample format.


  • Fixed tempo routine output duration inaccuracy due to rounding error
  • Implemented separate processing routines for integer and floating arithmetic to allow improvements to floating point routines (earlier used algorithms mostly optimized for integer arithmetic also for floating point samples)
  • Fixed a bug that distorts sound if sample rate changes during the sound stream
  • Fixed a memory leak that appeared in MMX/SSE/3DNow! optimized routines
  • Reduced redundant code pieces in MMX/SSE/3DNow! optimized routines vs. the standard C routines.
  • MMX routine incompatibility with new gcc compiler versions
  • Other miscellaneous bug fixes


  • Added automake/autoconf scripts for GNU platforms (in courtesy of David Durham)
  • Fixed SCALE overflow bug in rate transposer routine.
  • Fixed 64bit address space bugs.
  • Created a 'soundtouch' namespace for SAMPLETYPE definitions.


  • Added support for 32bit floating point sample data type with SSE/3DNow! optimizations for Win32 platform (SSE/3DNow! optimizations currently not supported in GCC environment)
  • Replaced 'make-gcc' script for GNU environment by master Makefile
  • Added time-stretch routine configurability to SoundTouch main class
  • Bugfixes


  • Moved SoundTouch under lesser GPL license (LGPL). This allows using SoundTouch library in programs that aren't released under GPL license.
  • Changed MMX routine organiation so that MMX optimized routines are now implemented in classes that are derived from the basic classes having the standard non-mmx routines.
  • MMX routines to support gcc version 3.
  • Replaced windows makefiles by script using the .dsw files


  • "mmx_gcc.cpp": Added "using namespace std" and removed "return 0" from a function with void return value to fix compiler errors when compiling the library in Solaris environment.
  • Moved file "FIFOSampleBuffer.h" to "include" directory to allow accessing the FIFOSampleBuffer class from external files.


  • Initial release

5.2. SoundStretch application Change History


  • Bugfixes in Wavfile: exception string formatting, avoid getLengthMs() integer precision overflow, support WAV files using 24/32bit sample format.


  • Added "-speech" switch to activate algorithm parameters more suitable for speech processing than the default parameters tuned for music processing.


  • Moved BPM detection routines from SoundStretch application into SoundTouch library
  • Allow using standard input/output pipes as audio processing input/output streams


  • Simplified accessing WAV files with floating point sample format.


  • Fixed 64bit address space bugs.


  • Added support for 32bit floating point sample data type
  • Restructured the BPM routines into separate library
  • Fixed big-endian conversion bugs in WAV file routines (hopefully :)


  • Fixed bugs in WAV file reading & added byte-order conversion for big-endian processors.
  • Moved SoundStretch source code under 'example' directory to highlight difference from SoundTouch stuff.
  • Replaced windows makefiles by script using the .dsw files
  • Output file name isn't required if output isn't desired (e.g. if using the switch '-bpm' in plain format only)


  • Fixed "Release" settings in Microsoft Visual C++ project file (.dsp)
  • Added beats-per-minute (BPM) detection routine and command-line switch "-bpm"


  • Initial release

6. Acknowledgements

Kudos for these people who have contributed to development or submitted bugfixes since SoundTouch v1.3.1:

  • Arthur A
  • Richard Ash
  • Stanislav Brabec
  • Christian Budde
  • Chris Bryan
  • Jacek Caban
  • Brian Cameron
  • Jason Champion
  • David Clark
  • Patrick Colis
  • Miquel Colon
  • Justin Frankel
  • Jason Garland
  • Takashi Iwai
  • Yuval Naveh
  • Paulo Pizarro
  • Blaise Potard
  • RJ Ryan
  • Patrick Colis
  • Miquel Colon
  • Sandro Cumerlato
  • Justin Frankel
  • Jason Garland
  • Masa H.
  • Takashi Iwai
  • Mathias M�hl
  • Yuval Naveh
  • Paulo Pizarro
  • Blaise Potard
  • RJ Ryan
  • John Sheehy
  • Tim Shuttleworth
  • John Stumpo
  • Tim Shuttleworth
  • Katja Vetter

Moral greetings to all other contributors and users also!


SoundTouch audio processing library Copyright (c) Olli Parviainen

This library is free software; you can redistribute it and/or modify it under the terms of the GNU Lesser General Public License version 2.1 as published by the Free Software Foundation.

This library is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public License for more details.

You should have received a copy of the GNU Lesser General Public License along with this library; if not, write to the Free Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA

RREADME.html file updated on 7-Jan-2014

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