VOICEBOX: Speech Processing Toolbox for MATLAB

Introduction

VOICEBOX is a speech processing toolbox consists of MATLAB routines that are maintained by and mostly written by Mike Brookes, Department of Electrical & Electronic Engineering, Imperial College, Exhibition Road, London SW7 2BT, UK. Several of the routines require MATLAB V6.5 or above and require (normally slight) modification to work with earlier veresions.

The routines are available as a  zip archive and are made available under the terms of the GNU Public License.

The routine VOICEBOX.M contains various installation-dependent parameters which may need to be altered before using the toolbox. In particular it contains a number of default directory paths indicating where temporary files should be created, where speech data normally resides, etc. You can override these defaults by editing voicebox.m directly or, more conveniently, by setting an environment variable VOICEBOX to the path of an initializing m-file. See the comments in voicebox.m for a fuller description.

For reading compressed SPHERE format files, you will need the SHORTEN program written by Tony Robinson and SoftSound Limited www.softsound.com. The path to the shorten executable must be set in voicebox.m.Unfortunately, the current version does not work on 64-bit systems.

MATLAB doesn't really like unicode fonts; some non-unicode fonts containing IPA phonetic symbols developed by SIL are available here.

Please send any comments, suggestions, bug reports etc to mike.brookes@ic.ac.uk.


Contents


Audio File Input/Output
Read and write WAV and other speech file formats
Frequency Scales
Convert between Hz, Mel, Erb and MIDI frequency scales
Fourier/DCT/Hartley Transforms
Various related transforms
Random Number and Probability Distributions
Generate random vectors and noise signals
Vector Distances
Calculate distances between vector lists
Speech Analysis
Active level estimation, Spectrograms
LPC Analysis of Speech
Linear Predictive Coding routines
Speech Synthesis
Text-to-speech synthesis and glottal waveform models
Speech Enhancement
Spectral noise subtraction
Speech Coding
PCM coding, Vector quantisation
Speech Recognition
Front-end processing for recognition
Signal Processing
Miscellaneous signal processing functions
Information Theory
Routines for entropy calculation and symbol codes
Computer Vision
Routines for 3D rotation
Printing and Display Functions
Utilities for printing and graphics
Voicebox Parameters and System Interface
Get or set VOICEBOX and WINDOWS system parameters
Utility Functions
Miscellaneous utility functions


Audio File Input/Output

Routines are available to read and, in some cases write, a variety of file formats:

Read Write Suffix  
readwav writewav .wav These routines allow an arbitrary number of channels and can deal with linear PCM (any precision up to 32 bits), A-law PCM, Mu-law PCM and Floating point formats. Large files can be read and written in small chunks.
readhtk writehtk .htk Read and write waveform and parameter files used by Microsoft's Hidden Markov Toolkit.
readsfs   .sfs Speech Filing system files from Mark Huckvale at UCL.
readsph   .sph NIST Sphere format files (including TIMIT). Needs SHORTEN for compressed files.
readaif   .aif AIFF format (Audio Interchange File Format) used by Mac users.
readcnx   cnx Read Connex database files (from BT)
readau   au Read AV audio files (from Sun)

Frequency Scale Conversion

From f To f Scale  
frq2bark bark2frq bark The bark scale is based on critical bands and masking in the human ear.
frq2cent cent2frq erb The cent scale is in increments of 0.01 semitones.
frq2erb erb2frq erb The erb scale is based on the equivalent rectangular bandwidths of the human ear.
frq2mel mel2frq mel The mel scale is based on the human perception of sinewave pitch.
frq2midi midi2frq midi The midi standard specifies a numbering of semitones with middle C being 60. They can use the normal equal tempered scale or else the pythagorean scale of just intonation. They will in addition output note names in a character format.

Fourier, DCT and Hartley Transforms

Forward Inverse  
rfft irfft Forward and inverse discrete fourier transforms on real data. Only the first half of the conjugate symmetric transform is generated. For even length data, the inverse routine is asumptotically twice as fast as the built-in MATLAB routine.
rsfft   Forward transform of real, symmetric data to give the first half only of the real, symmetric transform.
zoomfft   Calculate the discrete fourier transform at an arbitrary set of linearly spaced frequencies. Can be used to zoom into a subset of the full frequency range.
rdct irdct Forward and inverse discrete cosine transform on real data.
rhartley rhartley Hartley transform on real data (forward and inverse transforms are the same).

Random Numbers and Probability Distributions


Vector Distance

disteusq calculates the squared euclidean distance between all pairs of rows of two matrices.
distitar calculates the Itakura spectral distances between sets of AR coefficients.
distitpf calculates the Itakura spectral distances between power spectra.
distisar calculates the Itakura-Saito spectral distances between sets of AR coefficients.
distispf calculates the Itakura-Saito spectral distances between power spectra.
distchar calculates the COSH spectral distances between sets of AR coefficients.
distchpf calculates the COSH spectral distances between power spectra.

Speech Analysis

activlev calculates the active level of a speech segment according to ITU-T recommendation P.56.
activlevg calculates the active level of a speech segment robustly to added noise
dypsa estimates the glottal closure instants from the speech waveform.
enframe can be used to split a signal up into frames. It can optionally apply a window to each frame.
correlogram Calculates a 3D correlogram [slowly]
ewgrpdel calculates the energy-weighted group delay waveform.
fram2wav interpolates a sequence of frame-based value into a waveform
filtbankm Transformation matrix for a linear/mel/erb/bark-spaced filterbank from dft output
fxpefac PEFAC pitch tracker
fxrapt is an implementation of the RAPT pitch tracker by David Talkin.
gammabank Determine a bank of IIR gammatone filters
importsii calculate the SII importance function
mos2pesq Convert MOS values to PESQ speech quality scores
overlapadd Join frames up using overlap-add processing. Commonly used with enframe.
pesq2mos Convert PESQ speech quality scores to MOS values
phon2sone Convert signal levels from phons to sones
psycdigit experimental estimation of monotonic/unimodal psychometric function using TIDIGITS
psycest experimental estimation of monotonic psychometric function
psycestu experimental estimation of unimodal psychometric function
psychofunc calculate psychometric function
v_sigma estimate glottal opening and closure instants from the laryngograph/EGG waveform
snrseg calculate segmental SNR and global SNR relative to a reference signal
sone2phon Convert signal levels from sones to phons
soundspeed gives the speed of sound as a function of temperature
spgrambw draws a spectrogram with many options. See tutorial.
txalign finds the best alignment (in a least squares sense) between two sets of time markers (e.g. glottal closure instants).
vadsohn voice activity detector
v_ppmvu Calculate the PPM, VU or EBU levels of a signal

LPC Analysis of Speech

lpcauto &
lpccovar
perform linear predictive coding (LPC) analysis. The routines relating to LPC are described in more detail on another page. A large number of conversion routines are included for changing the form of the LPC coefficients (e.g. AR coefficients, reflection coefficients etc.): these are of the form lpcxx2yy where xx and yy denote the coefficient sets.
lpcrr2am calculates LPC filters for all orders up to a given maximum.
lpcbwexp performs bandwidth expansion on an LPC filter.
ccwarpf performs frequency warping in the complex cepstrum domain.
lpcifilt performs inverse filtering to estimate the glottal waveform from the speech signal and the lpc coefficients.
lpcrand can be used to generate random, stable filters for testing purposes.

Speech Synthesis

sapisynth Text-to-speech synthesis (TTS) of a string or matrix entries
glotros Calculates the Rosenberg model of the glottal flow waveform
glotlf Calculates the Liljencrants-Fant model of the glottal flow waveform

Speech Enhancement

estnoiseg uses an MMSE algorithm to estimate the noise spectrum from a noisy speech signal that has been divided into frames.
estnoisem uses a minimum-statistics algorithm to estimate the noise spectrum from a noisy speech signal that has been divided into frames.
specsub performs speech enhancement using spectral subtraction
ssubmmse performs speech enhancement using the MMSE or log MMSE criteria

Speech Coding

lin2pcma converts an audio waveform to 8-bit A-law PCM format
lin2pcmu converts an audio waveform to 8-bit mu-law PCM format
pcma2lin converts 8-bit A-law PCM to a waveform
pcmu2lin converts 8-bit mu-law PCM to a waveform
kmeanlbg vector quantisation using the LBG algorithm
kmeanhar vector quantisation using the K-harmonic means algorithm
potsband calculates a bandpass filter corresponding to the standard telephone passband.
v_kmeans vector quantisation using the K-means algorithm

Speech Recognition

melcepst implements a mel-cepstrum front end for a recogniser
melbankm constructs a bandpass filterbank with mel-spaced centre frequencies
cep2pow converts multivariate Gaussian means and covariances from the log power or cepstral domain to the power domain
pow2cep converts multivariate Gaussian means and covariances from the power domain to the log power or cepstral domain
ldatrace performs Linear Discriminant Analysis with optional constraints on the transform matrix

Signal Processing

ditherq adds dither and quantizes a signal
dlyapsq solves the discrete lyapunov equation using an efficient square root algorithm
filterbank Apply a bank of IIR filters to a signal
maxfilt performs running maximum filter
meansqtf calculates the output power of a rational filter with a white noise input
momfilt generate running moments from a signal
sigalign align a clean reference with a noise signal and find optimum gain
schmitt passes a signal through a schmitt trigger having hysteresis
teager calculate the Teager energy waveform
v_addnoise add noise to a signal at a chosen SNR
v_findpeaks finds the peaks in a signal
v_windows generates window functions
v_windinfo calculate window properties and figures of merit
zerocros finds the zero crossings of a signal with interpolation

Information Theory

huffman calculates optimum D-ary symbol code from a probability mass vector
entropy calculates entropy and conditional entropy for discrete and continuous distributions

Computer Vision

imagehomog Apply a homography transformation to an image with bilinear interpolation
polygonarea Calculates the area of a polygon
polygonwind Determines whether points are inside or outside a polygon
polygonxline Determines where a line crosses a polygon
qrabs Absolute value of a real quaternion
qrdivide divide two real quaternions (or invert one)
qrdotdiv elmentwise division of two real quaternion arrays
qrdotmult elmentwise multiplication of two real quaternion arrays
qrmult  multiply two real quaternion arrays
qrpermute permute the indices of a quaternion array
rectifyhomog Apply rectifing homographies to a set of cameras to make their optical axes parallel
rot--2-- converts between the following representations of rotations: rotation matrix (ro), euler angles (eu), axis of rotation (ax), plane of rotation (pl), real quaternion vector (qr), real quaternion matrix (mr), complex quaternion vector (qc), complex quaternion matrix (mc). A detailed description is given here.
rotqrmean Find the average of several rotation quaternions
rotqrvec Apply a quaternion rotation to an array of 3D vectors
skew3d Convert between vectors and skew symmetric matrices: 3x3 matrix <-> 3x1 vector and 4x4 Plucker matrix <-> 6x1 vector.
sphrharm forward and inverse spherical harmonic transform using uniform, Gaussian or arbitrary inclination (elevation) grids and a uniform azimuth grid.
upolyhedron Calculate the vertex coordinates and other characteristics of a uniform polyhedron

Printing and Display Functions

axisenlarge enlarge the axes of a figure slightly
bitsprec rounds values to a precision of n bits
cblabel add a label to the colourbar
figbolden makes the lines on a figure bold, enlarges font sizes and adjusts colours for printing clearly
fig2emf optionally makes the lines on a figure bold and then saves in windows metafile format
frac2bin converts numbers to fixed-point binary strings
lambda2rgb convert wavelength to an RGB or XYZ triplet
sprintsi prints a value with the correct standard SI multiplier (e.g. 2100 prints as 2.1 k)
texthvc add text to plots with specified alignment and colour
v_colormap set and display colormap information including colormaps that print well in monochrome
xticksi Label the x-axis tick marks using SI multipliers for large and small values. Particularly useful for logarithmic plots.
yticksi Label the y-axis tick marks using SI multipliers for large and small values. Particularly useful for logarithmic plots.
   

Voicebox Parameters and System Interface

voicebox contains a number of installation-dependent global parameters and is likely to need editing for each particular setup.
unixwhich searches the WINDOWS system path for an executable (like UNIX which command)
winenvar Obtains WINDOWS environment variables

Utility Functions

atan2sc arctangent function that returns the sin and cos of the angle
bitsprec Rounds values to a precision of n bits
choosenk all possible ways of choosing k elements out of the numbers 1:n without duplications
choosrnk all possible ways of choosing k elements out of the numbers 1:n with duplications allowed
dlyapsq Solve the discrete lyapunov equation
dualdiag simultaneously diagonalises two matrices: this is useful in computing LDA or IMELDA transforms.
finishat Estimate the finishing time of a long loop
fopenmkd Equivalent to FOPEN() but creates any missing directories/folders
hostipinfo Gives information about computer name and internet connections
logsum calculates log(sum(exp(x))) without overflow problems.
minspane Calculates the minimum spanning tree (a.k.a. shortest spanning tree) of a set of n-dimensional points
mintrace Find a row permutation to minimize the trace of a matrix
m2htmlpwd Create HTML documentation of matlab routines in the current directory
nearnonz Replace zero elements by the nearest non-zero elements
permutes all possible permutations of the numbers 1:n
quadpeak find a quadratically-interpolated peak in a N-dimensional array by fitting a quadratic function to the array values
rotation generates rotation matrices
zerotrim removes from a matrix any trailing rows and columns that are all zero.