Man page of CtuCopy
Section: CtuCopy - Speech Enhancement, Feature Extraction (1)
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CtuCopy - universal feature extractor and speech enhancer.
CtuCopy is a command line tool implementing speech enhancement and
feature extraction algorithms. It is similar to HCopy tool from
Cambridge's HTK and is partially compatible with it. CtuCopy acts as a
filter with speech waveform file(s) at the input and either a speech waveform file(s) or
feature file(s) at the output.
CtuCopy implements several speech enhancing methods based on spectral
subtraction. Extended Spectral Subtraction - exten [Sovka et al.,
EUSIPCO'96] combines Wiener filtering and spectral subtraction with
no need of a voice activity detector (VAD). Other methods are based on
spectral subtraction with VAD which can be either external (data read
from file) or internal (Burg's cepstral detector). The noise
suppression methods can be applied either directly to speech spectra
or to a spectra filtered by a bank of filters.
Bank of filters offers a set of frequency scales (melodic, Bark,
expolog, linear) and various filter shapes (triangular, rectangular,
trapezoidal same as time-domain IIR based implementation) which can be
combined to form standard and user-defined filter banks.
In feature extraction mode a number of common features can be
extracted from original or enhanced speech, e.g. LPC, PLP, MFCC or
magnitude spectrum. Current version also implements TRAP-DCT
features. Features can be saved either in HTK, pfile, or KALDI
CtuCopy recognizes these options:
Input speech file format.
<fmt> = raw - sequence of 16b integers
alaw - sequence of 8b integers, A-law encoded
mulaw - sequence of 8b integers, mu-law encoded
wave - MS wave file, PCM 16b, mono
- -format_out <fmt>
Output file format. This option also determines whether feature extraction
should be performed or not. Output format can either be a speech file
(raw, wave) or feature file (htk, pfile). In pfile case all input
files are saved to the only one output file which must be specified
by filename, see below.
<fmt> = raw - sequence of 16b integers
wave - MS wave file, PCM 16b, mono
htk - HTK feature file
pfile=<filename> - ICSI pfile.
ark=<filename> - KALDI ark,scp format.
- -endian_in <little|big>
Input byte order. Little endian means LSB..MSB, big endian the
opposite. Example: number 1 stored in two bytes looks like 10 for
little, and 01 for big endian. It does not apply to MS wave files,
which are read always in machine native format (displayed by CtuCopy
when invoked with -v).
- -endian_out <little|big>
Output byte order (see -endian_in). Applies only to raw and htk outputs. Otherwise
native order is used.
Input will be read from standard input. This option requires single file
mode at the output (output either to standard output or to a single
file specified with -o option). The input file size
is generally not known at the beginning, therefore for MS wave input
format the size in
file's header is ignored and the input is read until EOF.
Similar to -online_in. Requires single file mode at the input. Online
output is only applicable to output raw and htk formats which are
then saved with no header.
- -S <filename>
Specifies list of files to be processed. The filename structure
is one input and output filenames per line. Input and output are
separated by one or more tabs or spaces. When format_out is pfile, then
output string is discarded and a filename specified in -format_out option is
- -i <filename>
Single input file. This
option overrides the -S option. For debugging and testing purposes.
- -o <filename>
Single output file. See -i option.
- -preem <float>
Preemphasis factor to be applied to the input speech. Preemphasis
formula is y[k] = x[k] - preem*x[k-1]. Value has to be in the
range <0.0-1.0) and 0 means no preemphasis.
- -fs <int>
Sampling frequency in Hz. This option must be explicitly set as
it is used for computation of window sizes. MS wave files at the input
are checked to match this value before processing.
- -dither <float>
Dithering constant. A small dither can be added to the input
signal. Value 0.0 means no dither, 1.0 means random number in
range <-1,+1> at uniform distribution. 1.0 is default.
- -remove_dc <on|off>
Remove DC from every signal frame (done after preemphasis and
- -w <float>
Window size in milliseconds. The true window length in samples is
internally computed from sampling frequency.
- -s <float>
Window shift size in milliseconds. See -w option.
NOTE: When output is
speech, it is recommended to choose 50% or 75% overlap
(w/s = 2 or w/s = 4), otherwise there might be a significant ripple in
output signal envelope due to OLA. When invoked with -v option, CtuCopy computes
and prints out the maximum ripple for chosen values in % before computation.
- -fb_scale <scale>
Type of the frequency scale warping. By default CtuCopy designes a warped
version of the original frequency axis and further designes a set of filters which
are equidistant on the warped scale.
<scale> = mel - melodic scale (used in MFCC)
bark - Bark scale (used in original PLP)
lin - linear scale (no change)
expolog - special scale originally used for experiments with
Lombard speech by Hansen
- -fb_shape <shape>
Shape of filters. By default every shape has a predefined
overlap of subsequent filters (see below). When a different
overlap is needed, the filter
bank needs to be designed completely by the user using full -fb_definition
specification (see -fb_definition).
<shape> = triang - triangular shape with 50% overlap
rect - rectangular shape with no overlap
trapez - trapezoidal shape used in PLP analysis.
NOTE: Trapezoidal shape can only be used in PLP filter bank. As this
special shape is related to critical band theory, user cannot choose
number of filters in the bank, neither their positions. Thus, when
trapez shape is chosen, options -fb_scale and -fb_definition are
ignored and a special filter bank is designed.
NOTE 2: See BUGS section for more information on rectangular shape.
- -fb_norm <on|off>
Normalize filters to have unit area. Filters that are spread
uniformly on the warped frequency scale cover different number of
frequency bins of the underlying linear frequency scale as given by
FFT. When white noise enters the filter bank, it is no more white
after filtering. This option compensates for this effect.
- -fb_power <on|off>
Use FFT power spectrum at the input to the filter bank instead of
- -fb_eqld <on|off>
Apply a simplified Equal Loudness Curve to the filter bank,
prioritizing central frequencies (auditory-like operation). Note that
Equal Loudness is applied after possible normalization of filter area
- -fb_inld <on|off>
Apply Intensity Loudness Power Law (auditory-like operation). It is a
nonlinear operation applied independently to every frequency bin after
filtering the spectrum with a filter
bank. It is represented by a cube square root (compression of
- -fb_definition <string>
Defines location of all filters in the filter bank. The filter bank
consists of a number of filters that are fully described by
<string>. Filters can be split to several subsets. Every subset is
represented by one token. The token
describes a set of filters located equidistantly on the warped frequency
axis (specified by -fb_scale option); it specifies start and end
positions of the subset in Hz units and also how many filters should
be placed in that location. See more explanation below string
<string> = token[,token]...
X,Y ... frequency limits of this filter subset in
Hz. The first filter starts at X Hz, the last filter ends at
Y Hz, inclusively. If omitted, defaults to 0-fs/2.
N ... number of equidistant filters in the subset
K,L ... optionally specifies a subset of the above
filters (indexed from 1). If not specified, defaults to 1-N.
Most of the time only one token is used with the default settings. For
example, a MFCC filter bank with 25 filters can be specified with
"-fb_scale mel -fb_definition 25filters". It says "Place 25
equidistant filters on melodic scale from 0Hz to (fs/2)Hz.". More
examples can be found in examples section.
NOTE: There must NOT be any whitespace in <string>.
- -nr_mode <mode>
Algorithm for additive noise suppression. These algorithms are
accompanied by a number of options (see below)
which need to be properly set for a good performance. Is is
recommended to use presets (see -preset option) and then possibly modify the
<mode> = exten - Extended Spectral Subtraction
hwss - half-wave rectified spectral subtraction with VAD
fwss - full-wave rectified spectral subtraction with VAD
2fwss - 2-pass full-wave rectified s.s. with VAD
none - no noise reduction
- -nr_p <double>
Integration constant for spectral subtraction. It affects the
smoothness of noise/speech estimation via the formula "NewEstimate =
p * OldEstimate + (1 - p) * Observation". Should be
somewhere below 1.0.
- -nr_q <double>
VAD threshold used in internal Burg's cepstral detector.
- -nr_a <double>
Magnitude spectrum power constant for spectral subtraction. Defines a
domain where SS takes place. Normally either 1 (magnitude) or 2
(power) spectrum. However, any floating number can be used with some
performance drawback. Note that this option does not affect the domain
at the input to the filter bank, see option -fb_power for more.
- -nr_b <double>
Noise oversubtraction factor (applies to NR modes hwss and
fwss). It is a multiplicative factor applied to the noise estimate before
it is subtracted from the input speech-and-noise mixture.
- -nr_initsegs <int>
Number of initial frames in every input file that are guaranteed not
to contain any speech. It is used for initial estimate of noise in
algorithms hwss, fwss and 2fwss.
- -vad <string>
Specification of Voice Activity Detector (VAD). Applies to NR modes
hwss, fwss and 2fwss.
<string> = burg - built-in Burg's cepstral detector
file=<filename> - read VAD information from
File <filename> is a simple text file containing a sequence of
characters 0 or 1, one char for every input signal frame. 0 means no
speech in the frame , 1 means the opposite. For more
files at the input, there is only one VAD file containing as many
characters as there are overall frames at the input.
- -rasta <filename>
*** NOT SUPPORTED IN VERSION 3.0 ***
Perform RASTA filtering with impulse responses loaded from the file
- -nr_when <beforeFB,afterFB>
When used as feature extractor, this specifies whether noise reduction
should be done at the output of filter bank (afterFB) or rather before
applying the filter bank (beforeFB).
- -fea_kind <kind>
Specifies the type of output features and thus feature extraction
<kind> = spec - use directly the output of the filter bank as
logspec - logarithm of spec
lpa - Linear Predictive Coefficients. It means to take
power of filter bank outputs (unless -fb_inld is on), take iDFT, and
lpc - Linear Predictive Cepstrum. The same as for lpa plus
the recursion from LP coeffs to cepstral coeffs. Used e.g. in PLP.
dctc - Cepstrum obtained with DCT. It means taking log of
filter bank outputs and projecting to DCT bases. Used e.g. in MFCC.
trapdct,<int>,<int> - TRAP-DCT cepstral coeffs calculated
from log mel spectra. First arg is TRAP length in frames, second arg
is the number of the first DCT coefficients to save per band.
Per-frame log mels are buffered and on their temporal trajectories (the current
frame plus a symmetrical window) a Hamming window is applied followed by DCT
transform. This is done independently in all frequency bands.
td-iir-mfcc - MFCC-like features which are based on the bank of IIR
filters with frequency responses close to standard triangular MFCC
filter-bank. Input signal is filtered by the set of distinct IIR
filters in the time domain and band power spectrum is then obtained by
the computation of short-time power of each particular band signal
from the time window of the length specified by -w and -s
optionn. Next steps (logarithm and DCT application) are same as for
the standard approach of MFCC computation.
- -fea_delta <kind>
Specifies the type of output differential feats.
<kind> = d - compute dynamic diff. coefficients (delta)
d_a - compute dynamic, acceleration diff. coefficients (delta-delta-delta)
d_a_t - compute dynamic, acceleration, third diff. coefficients (delta-delta-delta-delta-delta-delta)
- -fea_trap <int>
The creation of context information from features defined by
-fea_kind. The context information is caught using context window of
specified length created from several neighbouring short-time frames
(stacked features). The context window size is specified by the
integer value (number of frames; the value 5 => cw=5+5+1, i.e. the
length of context widnow equal to 11)
- -fea_lporder <int>
Order of Linear Predictive model (when applicable).
- -fea_ncepcoeffs <int>
When applicable, number of cepstral coefficients included in the feature vector. It
does not include c0, which has its own option -fea_c0.
- -fea_c0 <on|off>
Add zeroth cepstral coefficient to the feature vector if
- -fea_E <on|off>
Add log of frame energy to the feature vector. Log energy is defined for every
fea_kind as follows:
fea_kind = spec/logspec/lpa/lpc: log of frame energy after passing through Noise
Reduction and Filter Bank blocks. It is identical to the log of the zeroth
fea_kind = dctc: Energy is computed always before Filter Bank
block. When Noise Reduction takes place after Filter bank, it is
computed from input spectra; otherwise it is computed from spectra
after Noise Reduction.
NOTE: These definitions can be overriden by the -fea_rawenergy
- -fea_rawenergy <on|off>
Compute frame energy directly from the input signal frame before doing
anything (preemphasis, Hamming, FFT), ignoring fea_kind.
- -fea_lifter <int>
Cepstrum liftering constant. Value of 1 means no liftering. Otherwise
it is defined as in HTK book.
- -fea_Z_block <int>
Average cepstrum is computed on the basis of moving average over the
fixed time interval. Integer value of fea_Z_block correspodns to the
length of moving window in miliseconds across which average cepstrum
is computed. Value 5000 means the window length equal to 5s, value of
-1 means no CMS.
- -fea_Z_exp <int>
Average cepstrum is computed on the basis of recursive exponential
moving average. Integer value of fea_Z_exp corresponds to the time
constant in miliseconds (equivalent window size) across which average
cepstrum is computed. Value 5000 means the window length equal to 5s,
value of -1 means no CMS.
- -stat_cmvn <filename>
The cepstrum mean and variance statistics are computed on the basis of
given input list for feature extraction (usually grouping utterances
of particular speakers; see examples/run.sh script) and saved to the
specified output file for further application using .apply_cmvn
- -apply_cmvn <filename>
The cepstrum mean and variance normalization is done on the basis
of loaded CMVN statistics precomputed using the -stat_cmvn option and
saved in the specified file.
- -preset <type>
Apply a preset to the above options. This macro option behaves just like any
other option. Applied settings can be overriden by any command line
option following the -preset option.
To see exactly what has changed after using the -preset option, it is
recommended to use -v option and check the program output. For macro
definitions, see below.
<type> = mfcc - MFCC computation similar to what HTK does
equivalent is: "-fb_scale mel -fb_shape triang
-fb_power on -fb_definition 1-26/26filters
-nr_mode none -fb_eqld off -fb_inld off -fea_kind dctc -fea_ncepcoefs 12 -fea_c0 on
-fea_E off -fea_lifter 22 -fea_rawenergy off"
plpc - suitable for PLP computation similar to the original
- Hermansky paper (Bark scale, trapezoidal filters).
equivalent is: "-fb_scale bark -fb_shape trapez
-fb_power on -fb_definition 1-15/15filters
-nr_mode none -fb_eqld on -fb_inld on -fea_kind lpc -fea_lporder 12 -fea_ncepcoefs
- 12 -fea_c0 on -fea_E off -fea_lifter 22 -fea_rawenergy off"
exten - suitable for speech enhancement using Extended
- Spectral Subtraction.
equivalent is: "-w 32 -s 10 -fb_definition none
-fb_scale none -fb_shape none -nr_a 2 -fb_eqld off -fb_inld off -fb_power off
-fb_norm off -nr_mode exten -fea_kind none -fea_c0 off -fea_E off -fea_lifter 0
- Note that by default CtuCopy acts as a feature extractor with
pseudo-PLP features, mel scale, triangular filters.
- -verbose, -v
Verbose mode. Prints generally more, also prints all warnings and
at the beginning also prints overall program settings. Highly recommended for
debugging, optimizations and fine-tuning.
Suppress console output. Only error messages related to a premature program
termination are printed.
Prints overall program settings at the beginning.
- -C <filename>
Specifies configuration file. Configuration file acts as a set of command
line options. Configuration file is always parsed before any other
options on the command line.
SYNTAX: It is a text file with one command line option per line. Empty lines and
whitespace are allowed. Comments are allowed, they begin with
character #. Any text following # up to the end of line is
- -h, --help
Print brief version of this text and exit.
Speech enhancement with one file:
ctucopy -preset exten -fs 16000 -format_in wave -format_out wave -i input.wav -o output.wav -v
This loads a preset for speech enhancement using extended spectral
subtraction, then sets sampling frequency to 16 kHz, sets input and
output formats to MS wave and after a specification of input and output
files sets the verbose flag to on so that program prints out full
settings and also number of frames processed.
- Online speech enhancement:
ctucopy -preset exten -fs 8000 -format_in raw -format_out raw -online_on -online_out < input > output
Reads 16 bit mono PCM data from stdin until EOF in machine
native byte order and writes the enhanced output to stdout.
- Feature extraction using default settings:
ctucopy -fs 8000 -format_in wave -format_out htk -endian_out big -S list.txt
Reads MS Wave files specified in the first column of the file
list.txt, computes 13 speech features per frame and saves the results
to HTK files specified in the second column of the file list.txt.
- Feature extraction of HTK MFCCs:
ctucopy -fs 8000 -format_in wave -format_out htk -endian_out big -preset mfcc -S list.txt
The same as above, but with feature extraction settings suitable for
- Feature extraction of original PLPs to a pfile:
ctucopy -fs 8000 -format_in wave -format_out pfile=features.pfile -preset plp -S list.txt
- Using config file with the settings from the previous example:
ctucopy -C config.txt
Contents of config.txt:
# CtuCopy config file
-fs 8000 # sampling freq
-format_in wave # MS wave
-S list.txt # 2nd column of list.txt will be ignored
- Advanced example of feature extraction:
ctucopy -format_in raw -endian_in big -fs 8000 -format_out htk -endian_out big -S list.txt -preem 0.97 -fb_scale expolog -fb_shape rect -fb_eqld off -fb_definition 0-3000Hz:3-5/5filters,3000-4000Hz:1-1/1filters -nr_mode 2fwss -vad burg -nr_when beforeFB -fea_kind lpc -v
Reads raw 16 bit mono PCM files in big endian coding from the input
and saves the output to HTK files. Uses preemphasis. Filter bank is
designed on expolog scale with rectangular filters with no
overlap. Filter bank consists of the following filters. First, take
the expolog scale and use an area from 0 Hz to 3000 Hz. Add to the
filter bank the 3rd,
4th and 5th filter out of 5 filters that would be placed equidistantly
in that part of frequency axis. Second, add one
more filter to the filter bank that starts at 3000 Hz and ends at 4000
Hz. For noise suppression use two-pass spectral subtraction algorithm
with internal Burg's VAD and perform the noise suppression before the
filter bank. Compute LP cepstral coefficients. Be verbose so that
settings can be double checked.
- The other examples, how to work with ctucopy4 (CMVN, CMS, output in KALDI format) tool you can find in examples/run.sh script.
Please report all bugs not mentioned below to the author.
- In speech enhancement mode the amplitude spectrum is modified. It
- affects the dynamics of the signal which does not necessarily fit the
16 bit range upon reconstruction. Thus, when a signal sample is bigger than
the available dynamic range and the -v option is set, a warning
message is printed locating the problematic sample and the sample is clipped. When the sample is
larger than (2 x max value), then a warning message is printed always (unless quiet mode) and the sample is clipped.
- In speech enhancement mode the input and output signal lengths do
- not generally match. The input signal is read frame by frame until
there are not enough samples for a full frame. It means the signal is
cut at the position of the last available frame.
- MS Wave input and output formats do not support switching of byte
- order. They are always read in machine native format.
- When an external VAD file is used, there is no guarantee that the
- framing matches the input signal. User has to check this.
- In online mode no headers are written at the output (including HTK
- format) and for MS Wave input the number of samples from the file header
- RASTA filtering is not implemented in current version.
- Filter bank design: In case of rectangular window, filters are designed
- not to have any overlap. In any subset of filters (specified with start and stop
frequencies) the boundary bins are by default included so that the design is
intuitive. However, if there exist any two subsets that are
joined (one ends at the point where the other begins), the bin common to both
is only present in the lower subset so that there is no overlap "in the middle".
Petr Mizera <email@example.com>
Petr Fousek <firstname.lastname@example.org>
Petr Pollak <email@example.com>
with kind help of Prague SpeechLab members.
The first ctucopy version was built on exten, an original implementation
of Extended Spectral Subtraction by Pavel Sovka, Petr Pollak and Jan Kybic,
P. Sovka, P. Pollak, J. Kybic, "Extended Spectral Subtraction", EUSIPCO'96, Trieste, 1996.
Once completed, it was published as an open source project on Interspeech 2003,
P. Fousek, P. Pollak, "Additive Noise and Channel Distortion-Robust Parametrization Tool - Performance Evaluation on Aurora 2 & 3", Eurospeech'03, Geneva, 2003.
Later within a study of Lombard effect, an implementation of filter banks
was much generalized and rewritten,
H. Boril, P. Fousek, P. Pollak, "Data-Driven Design of Front-End Filter bank for Lombard Speech Recognition", ICSLP'06, Pittsburgh, 2006.
In 2012, as a reaction to enquiries of commercial subjects, ctucopy was released under Apache 2.0 licence.
Next work was focused on various cepstral normalization techniques like CMVN, various CMS.
M. Borsky, P. Mizera, P. Pollak, "Noise and Channel Normalized Cepstral Features for Far-Speech Recognition", In Speech and Computer. Cham: Springer International
Publishing AG, 2013.
The support KALDI format was added in work on ISP 2015.
P. Mizera, P. Pollak, M. Borsky, A. Kolman, M. Ernestus, "Towards the DNN-HMM Recognition of Czech Casual Speech", SUBMITTED TO Interspeech 2015.
Copyright 2013 Petr Fousek and FEE CTU Prague
Copyright 2015 Petr Mizera and FEE CTU Prague
Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at
Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.
This document is valid for CtuCopy versions 3.0 - 4.0
- FILTER BANK:
- NOISE REDUCTION:
- FEATURE EXTRACTION:
This document was created by
using the manual pages.
Time: 14:02:21 GMT, April 08, 2015