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ch_wave

Audio file manipulation

# Synopsis

ch_wave is used to manipulate the format of a waveform file. Operations include:

- file format conversion
- resampling (changing the sampling frequency)
- byte-swapping
- making multiple input files into a single multi-channel output file
- making multiple input files into a single single-channel output file
- extracting a single channel from a multi-channel waveform
- scaling the amplitude of the waveform
- low pass and high pass filtering
- extracting a time-delimited portion of the waveform

ch_wave is a executable program that serves as a wrap-around for the EST_Wave class and the basic wave manipulation functions. More advanced waveform processing is performed by the signal processing library.

# Options

# Making multiple waves into a single wave

If multiple input files are specified, by default they are concatenated into the output file.

    $ ch_wave kdt_010.wav kdt_011.wav kdt_012.wav kdt_013.wav -o out.wav

In the above example, 4 single channel input files are converted to one single channel output file. Multi-channel waveforms can also be concatenated provided they all have the same number of input channels.

Multiple input files can be made into a multi-channel output file by using the -pc option:

    $ ch_wave kdt_010.wav kdt_011.wav kdt_012.wav kdt_013.wav -o -pc LONGEST out.wav

The argument to -pc can either be LONGEST, in which the output waveform is the length of the longest input file, or FIRST in which it is the length of the first input file.

# Extracting channels from multi-channel waves

The -c option is used to specify channels which should be extracted from the input. If the input is a 4 channel wave,

    $ ch_wave kdt_m.wav -o a.wav -c "0 2"

will extract the 0th and 2nd channel (counting starts from 0). The argument to -c can be either a single number of a list of numbers (wrapped in quotes)

# Extracting of a single region from a waveform

There are several ways of extracting a region of a waveform. The simplest way is by using the start, end, to and from commands to delimit a sub portion of the input wave. For example,

    $ ch_wave kdt_010.wav -o small.wav -start 1.45 -end 1.768

extracts a subwave starting at 1.45 seconds and extending to 1.768 seconds.

Alternatively,

    $ ch_wave kd_010.wav -o small.wav -from 5000 -to 10000

extracts a subwave starting at 5000 samples and extending to 10000 samples. Times and samples can be mixed in sub-wave extraction. The output waveform will have the same number of channels as the input waveform.

# Extracting of a multiple regions from a waveform

Multiple regions can be extracted from a waveform, but as it would be too complicated to specify the start and end points on the command line, a label file with start and end points, and file names is used.

The file is called a key label file and in xwaves label format looks like:

    separator ;
    #
    0.308272  121 sil ;     file kdt_010.01 ;
    0.440021  121 are ;     file kdt_010.02 ;
    0.512930  121 your ;    file kdt_010.03 ;
    0.784097  121 grades ;  file kdt_010.04 ;
    1.140969  121 higher ;  file kdt_010.05 ;
    1.258647  121 or ;      file kdt_010.06 ;
    1.577145  121 lower ;   file kdt_010.07 ;
    1.725516  121 than ;    file kdt_010.08 ;
    2.315186  121 nancy's ; file kdt_010.09 ;

Each line represents one region. The first column is the end time of that region and the start time of the next. The next two columns are colour and an arbitrary name, and the filename in which the output waveform is to be stored is kept as a field called file in the last column. In this example, each region corresponds to a single word in the file.

If the above file is called "kdt_010.words.keylab", the command:

    $ ch_wave kdt_010.wav -key kdt_010.words -ext .wav -divide

will divide the input waveform into 9 output waveforms called kdt_010.01.wav, kdt_010.02.wav ... kdt_010.09.wav. The -ext option specifies the extension of the new waveforms, and the -divide command specifies that division of the entire waveform is to take place.

If only a single file is required the -extract option can be used, in which case its argument is the filename required.

    $ ch_wave kdt_010.wav -key kdt_010.words -ext .wav -extract kdt_010.03 \
          -o kdt_010.03.wav

Note that an output filename should be specified with this option.

# Adding headers and format conversion

It is usually a good idea for all waveform files to have headers as this way different byte orders, sampling rates etc can be handled safely. ch_wave provides a means of adding headers to raw files.

The following adds a header to a file of 16 bit shorts

    $ ch_wave kdt_010.raw1 -o kdt_010.h1.wav -otype nist -f 16000 -itype raw

The following downsamples the input to 8 KHz

    $ ch_wave kdt_010.raw1 -o kdt_010.h2.wav -otype nist -f 16000  \
              -F 8000 -itype raw

The following takes a 8K ulaw input file and produces a 16bit, 20Khz output file:

    $ ch_wave kdt_010.raw2 -o kdt_010.h3.wav -otype nist -istype ulaw \
                  -f 8000 -F 20000 -itype raw