[ViewVC] Annotation of: cvs/PDL-Audio/README

NAME
    PDL::Audio - Some PDL functions intended for audio processing.

SYNOPSIS
      use PDL;
      use PDL::Audio;

DESCRIPTION
    Oh well ;) Not much "introductory documentation" has been written yet :(

  NOTATION
    Brackets around parameters indicate that the respective parameter is
    optional and will be replaced with some default value when absent (or
    "undef", which might be different in other packages).

    The sampling frequency and duration are by default (see individual
    descriptions) given in cycles/sample (or samples in case of a duration).
    That means if you want to specify a duration of two seconds, you have to
    multiply by the sampling frequency in HZ, and if you want to specify a
    frequency of 440 Hz, you have to divide by the sampling frequency:

     # Syntax: gen_oscil duration*, frequency/
     $signal = gen_oscil 2*HZ, 440/HZ;
     # with a sampling frequency of 44100 Hertz:
     $signal = gen_oscil 2*44100, 440/44100;

    To help you, the required unit is given as a type suffix in the
    parameter name. A "/" means that you have to divide by the sampling
    frequency (to convert from Hertz) and a suffix of "*" indicates that a
    multiplication is required.

    Most parameters named "size", "duration" (or marked with "*") can be
    replaced by a piddle, which is then used to give length and from
    (mono/stereo).

  HEADER ATTRIBUTES
    The following header attributes are stored and evaluated by most
    functions. PDL::Audio provides mutator methods for all them (e.g.

     print "samplerate is ", $pdl->rate;
     $pdl->comment("set the comment to this string");

    rate
        The sampling rate in hz.

    filetype
        The filetype (wav, au etc..). Must be one of:

          FILE_NEXT FILE_AIFC FILE_RIFF FILE_BICSF FILE_NIST FILE_INRS FILE_ESPS
          FILE_SVX FILE_VOC FILE_SNDT FILE_RAW FILE_SMP FILE_SD2 FILE_AVR
          FILE_IRCAM FILE_SD1 FILE_SPPACK FILE_MUS10 FILE_HCOM FILE_PSION
          FILE_MAUD FILE_IEEE FILE_DESKMATE FILE_DESKMATE_2500 FILE_MATLAB
          FILE_ADC FILE_SOUNDEDIT FILE_SOUNDEDIT_16 FILE_DVSM FILE_MIDI
          FILE_ESIGNAL FILE_SOUNDFONT FILE_GRAVIS FILE_COMDISCO FILE_GOLDWAVE
          FILE_SRFS FILE_MIDI_SAMPLE_DUMP FILE_DIAMONDWARE FILE_REALAUDIO
          FILE_ADF FILE_SBSTUDIOII FILE_DELUSION FILE_FARANDOLE FILE_SAMPLE_DUMP
          FILE_ULTRATRACKER FILE_YAMAHA_SY85 FILE_YAMAHA_TX16 FILE_DIGIPLAYER
          FILE_COVOX FILE_SPL FILE_AVI FILE_OMF FILE_QUICKTIME FILE_ASF
          FILE_YAMAHA_SY99 FILE_KURZWEIL_2000 FILE_AIFF FILE_AU

    path
        The filename (or file specification) used to load or save a file.

    format
        Specifies the type the underlying file format uses. The samples will
        always be in short or long signed format.

        Must be one of

           FORMAT_NO_SND FORMAT_16_LINEAR FORMAT_8_MULAW FORMAT_8_LINEAR
           FORMAT_32_FLOAT FORMAT_32_LINEAR FORMAT_8_ALAW FORMAT_8_UNSIGNED
           FORMAT_24_LINEAR FORMAT_64_DOUBLE FORMAT_16_LINEAR_LITTLE_ENDIAN
           FORMAT_32_LINEAR_LITTLE_ENDIAN FORMAT_32_FLOAT_LITTLE_ENDIAN
           FORMAT_64_DOUBLE_LITTLE_ENDIAN FORMAT_16_UNSIGNED
           FORMAT_16_UNSIGNED_LITTLE_ENDIAN FORMAT_24_LINEAR_LITTLE_ENDIAN
           FORMAT_32_VAX_FLOAT FORMAT_12_LINEAR FORMAT_12_LINEAR_LITTLE_ENDIAN
           FORMAT_12_UNSIGNED FORMAT_12_UNSIGNED_LITTLE_ENDIAN COMPATIBLE_FORMAT

        PDL::Audio conviniently defines the following aliases for the
        following constants, that are already correct for the host
        byteorder:

           FORMAT_ULAW_BYTE FORMAT_ALAW_BYTE FORMAT_LINEAR_BYTE
           FORMAT_LINEAR_SHORT FORMAT_LINEAR_USHORT FORMAT_LINEAR_LONG
           FORMAT_LINEAR_FLOAT FORMAT_LINEAR_DOUBLE

    comment
        The file comment (if any).

    device
        The device to output audio. One of:

           DEV_DEFAULT DEV_READ_WRITE DEV_ADAT_IN DEV_AES_IN DEV_LINE_OUT
           DEV_LINE_IN DEV_MICROPHONE DEV_SPEAKERS DEV_DIGITAL_IN DEV_DIGITAL_OUT
           DEV_DAC_OUT DEV_ADAT_OUT DEV_AES_OUT DEV_DAC_FILTER DEV_MIXER
           DEV_LINE1 DEV_LINE2 DEV_LINE3 DEV_AUX_INPUT DEV_CD_IN DEV_AUX_OUTPUT
           DEV_SPDIF_IN DEV_SPDIF_OUT
   
  EXPORTED CONSTANTS
    In addition to the exported constants described above (and later in the
    function descriptions), this module also exports the mathematical
    constants M_PI and M_2PI, so watch out for clashes!

FUNCTIONS
  sound_format_name format_code
    Return the human-readable name of the file format with code
    "format_code".

  sound_type_name type_code
    Return the human-readable name of the sample type with code "type_code".

  describe_audio piddle
    Describe the audio stream contained in piddle and return it as a string.
    A fresh piddle might return:

     mono sound with 27411 samples

    Whereas a freshly loaded soundfile might yield:

     stereo sound with 27411 samples, original name "kongas.wav", type 2 (RIFF),
     rate 11025/s (duration 2.49s), format 7 (8-bit unsigned)

  raudio path, [option-hash], option => value, ...
    Reads audio data into the piddle. Options can be anything, most useful
    values are "filetype", "rate", "channels" and "format". The returned
    piddle is represents "time" in the outer dimension, and samples in the
    inner (i.e. scalars for mono files, 2-vectors for stereo files):

     [ [left0, right0], [left1, right1], ...

     # read any file
     $pdl = raudio "file.wav";
     # read a file. if it is a raw file preset values
     $pdl = raudio "file.raw", filetype => FILE_RAW, rate => 44100, channels => 2;

  waudio pdl, [option-hash], option => value, ...
    Writes a pdl as a file. The path is taken from the header (or the
    options), e.g.:

     # write a file, using the header of another piddle
     $pdl->waudio ($orig_file->gethdr);
     # write pdl as au file, take rate from the header
     $pdl->waudio (path => "piddle.au", filetype => FILE_AU, format => FORMAT_16_LINEAR;

  cut_leading_silence pdl, level
    Cuts the leading silence (i.e. all samples with absolute value < level)
    and returns the resulting part.

  cut_trailing_silence pdl, level
    Cuts the trailing silence.

  cut_silence pdl, level
    Calls "cut_leading_silence" and "cut_trailing_silence" and returns the
    result.

  playaudio pdl, [option-hash], option => value ...
    Play the piddle as an audio file. Options can be supplied either through
    the option hash (a hash-reference), through the pdl header or the
    options:

     # play a piddle that has a valid header (e.g. from raudio)
     $pdl->playaudio;
     # play it with a different samplerate
     $pdl->playaudio(rate => 22050);

  ulaw2linear
      Signature: (byte u(n); short [o] s(n))

    conversion from (m)u-law into signed, linear, 16 bit samples (rather
    slow)

  linear2ulaw
      Signature: (short s(n); byte [o] u(n))

    conversion from signed, linear, 16 bit samples into (m)u-law (rather
    slow)

  alaw2linear
      Signature: (byte u(n); short [o] s(n))

    conversion from A-law into signed, linear, 16 bit samples (rather slow)

  linear2alaw
      Signature: (short s(n); byte [o] u(n))

    conversion from signed, linear, 16 bit samples into A-law (rather slow)

  gen_oscil duration*, freq/, phase-mod, [fm-mod/]
  gen_sawtooth duration*, freq/, phase-mod, [fm-mod/]
  gen_square duration*, freq/, phase-mod, duty, [fm-mod/]
  gen_triangle duration*, freq/, phase-mod, [fm-mod/]
  gen_pulse_train duration*, freq/, phase-mod, [fm-mod/]
  gen_rand duration*, freq/
  gen_rand_1f duration*
    All of these functions generate appropriate waveforms with frequency
    "freq" (cycles/sample) and phase "phase" (0..1).

    The "duration" might be either a piddle (which gives the form of the
    output) or the number of samples to generate.

    The output samples are between -1 and +1 (i.e. "-1 <= s <= +1").

    The "duty" parameter of the square generator influences the duty cycle
    of the signal. Zero means 50%-50%, 0.5 means 75% on, 25% off, -0.8 means
    10% on, 90% off etc... Of course, the "duty" parameter might also be a
    vector of size "duration".

  gen_env duration*, xvals, yvals, [base]
    Generates an interpolated envelope between the points given by xvals and
    yvals. When base == 1 (the default) then the values will be linearly
    interpolated, otherwise they follow an exponential curve that is bend
    inwards (base < 1) or outwards (base > 1).

     # generate a linear envelope with attack in the first 10%
     gen_env 5000, [0 1 2 9 10], [0 1 0.6 0.6 0];

  gen_adsr duration*, sustain-level, attack-time, decay-time, sustain-time, release-time
    Simple ADSR envelope generator. The "sustain-level" is the amplitude (0
    to 1) of the sustain level. The other for parameters give the relative
    interval times, in any unit you like, only their relative ratios are
    important. Any of these times might be zero, in which case the
    corresponding part is omitted from the envelope.

  gen_asymmetric_fm duration*, freq/, phase, [r , [ratio]]
    "gen_asymmetric_fm" provides a way around the symmetric spectra normally
    produced by FM. See Palamin and Palamin, "A Method of Generating and
    Controlling Asymmetrical Spectra" JAES vol 36, no 9, Sept 88, p671-685.

  gen_sum_of_cosines duration*, freq/, phase, ncosines, [fm_mod/]
    Generates a sum of "n" cosines "(1 + 2(cos(x) + cos(2x) + ... cos(nx)) =
    sin((n+.5)x) / sin(x/2))". Other arguments are similar to to
    "gen_oscil".

  gen_sine_summation duration*, freq/, phase, [nsines, [a, [b_ratio, [fm_mod/]]]]
    "gen_sine_summation" provides a kind of additive synthesis. See
    J.A.Moorer, "Signal Processing Aspects of Computer Music" and "The
    Synthesis of Complex Audio Spectra by means of Discrete Summation
    Formulae" (Stan-M-5). The basic idea is very similar to that used in
    gen_sum_of_cosines generator.

    The default value for "nsines" is 1 (but zero is a valid value), for "a"
    is 0.5 and for "b_ratio" is 1.

    (btw, either my formula is broken or the output indeed does not lie
    between -1 and +1, but rather -5 .. +5).

  gen_from_table duration*, frequency/, table, [phase], [fm_mod/]
    "gen_from_table" generates a waveform by repeating a waveform given in
    "table", linearly interpolating between successive points of the
    "waveform".

  partials2waveshape size*, partials, amplitudes, [phase], [fm_mod/]
    Take a (perl or pdl) list of (integer) "partials" and a list of
    "amplitudes" and generate a single wave shape that results by adding
    these partial sines.

    This could (and should) be used by the "gen_from_table" generator.

  gen_from_partials duration*, frequency/, partials, amplitudes, [phase], [fm_mod/]
    Take a (perl list or pdl) list of (possibly noninteger) "partials" and a
    list of "amplitudes" and generate the waveform resulting by summing up
    all these partial sines.

  filter_one_zero
      Signature: (in(n); [o] out(n); double a0; double a1)

    apply a one zero filter, y(n) = a0 x(n) + a1 x(n-1)

  filter_one_pole
      Signature: (in(n); [o] out(n); double a0; double b1)

    apply a one pole filter, y(n) = a0 x(n) - b1 y(n-1)

  filter_two_zero
      Signature: (in(n); [o] out(n); double a0; double a1; double a2)

    apply a two zero filter, y(n) = a0 x(n) + a1 x(n-1) + a2 x(n-2)

  filter_two_pole
      Signature: (in(n); [o] out(n); double a0; double b1; double b2)

    apply a two pole filter, y(n) = a0 x(n) - b1 y(n-1) - b2 y(n-2)

  filter_formant
      Signature: (in(n); [o] out(n); double radius; double frequency; double gain)

    apply a formant filter, y(n) = x(n) - r*x(n-2) +
    2*r*cos(2*pi*frequency)*y(n-1) - r*r*y(n-2). A good value for "gain" is
    1.

  filter_ppolar pdl, radius/, frequency/
    apply a two pole filter (given in polar form). The filter has two poles,
    one at (radius,frequency), the other at (radius,-frequency). Radius is
    between 0 and 1 (but less than 1), and frequency is between 0 and 0.5.
    This is the standard resonator form with poles specified by the polar
    coordinates of one pole.

  filter_zpolar pdl, radius/, frequency/
    apply a two zero filter (given in polar form). See "filter_ppolar".

  partials2polynomial partials, [kind]
    "partials2polynomial" takes a list of harmonic amplitudes and returns a
    list of Chebychev polynomial coefficients. The argument "kind"
    determines which kind of Chebychev polynomial we are interested in, 1st
    kind or 2nd kind. (default is 1).

  ring_modulate in1, in2
    ring modulates in1 with in2 (this is just a multiply).

  amplitude_modulate am_carrier, in1, in2
    amplitude modulates am_carrier and in2 with in1 (this calculates in1 *
    (am_carrier + in2)).

  filter_sir
      Signature: (x(n); a(an); b(bn); [o]y(n))

    Generic (short delay) impulse response filter. "x" is the input signal
    (which is supposed to be zero for negative indices). "a" contains the
    input (x) coefficients (a0, a1, .. an), whereas "b" contains the output
    (y) coefficients (b0, b1, ... bn), i.e.:

     y(n) = a0 x(n) - b1 y(n-1) + a1 x(n-1) - b2 y(n-2) + a2 x(n-2) - b3 ...

    This can be used to generate fir and iir filters of any length, or even
    more complicated constructs.

    "b0" (then first element of "b") is being ignored currently AND SHOULD
    BE SPECIFIED AS ONE FOR FUTURE COMPATIBILITY

  filter_lir
      Signature: (x(n); int a_x(an); a_y(an); int b_x(bn); b_y(bn); [o]y(n))

    Generic (long delay) impulse response filter. The difference to
    "filter_sir" is that the filter coefficients need not be consecutive,
    but instead their indices are given by the "a_x" and "b_x" (integer)
    vectors, while the corresponding coefficients are in "a_y" and "b_y".
    (All "a_x" must be >= 0, while all the "b_x" must be >= 1, as you should
    expect).

    See "filter_sir" for more info.

  filter_fir input, xcoeffs
    Apply a fir (finite impulse response) filter to "input". This is the
    same as calling:

     filter_sir input, xcoeffs, pdl()

  filter_iir input, ycoeffs
    Apply a iir (infinite impulse response) filter to "input". This is just
    another way of saying:

     filter_sir input, pdl(1), ycoeffs

    That is, the first member of "ycoeffs" is being ignored AND SHOULD BE
    SPECIFIED AS ONE FOR FUTURE COMPATIBILITY!

  filter_comb input, delay*, scaler
    Apply a comb filter to the piddle "input". This is implemented using a
    delay line of length "delay" (which must be 1 or larger and can be
    non-integer) and a feedback scaler.

     y(n) = x(n-size-1) + scaler * y(n-size)

    cf. "filter_notch" and
    http://www.harmony-central.com/Effects/Articles/Reverb/comb.html

  filter_notch input, delay*, scaler
    Apply a comb filter to the piddle "input". This is implemented using a
    delay line of length "delay" (which must be 1 or larger and can be
    non-integer) and a feedforward scaler.

     y(n) = x(n-size-1) * scaler + y(n-size)

    As a rule of thumb, the decay time of the feedback part is
    "7*delay/(1-scaler)" samples, so to get a decay of Dur seconds, "scaler
    <= 1-7*delay/(Dur*Srate)". The peak gain is "1/(1-(abs scaler))". The
    peaks (or valleys in notch's case) are evenly spaced at "srate/delay".
    The height (or depth) thereof is determined by scaler -- the closer to
    1.0, the more pronounced. See Julius Smith's "An Introduction to Digital
    Filter Theory" in Strawn "Digital Audio Signal Processing", or Smith's
    "Music Applications of Digital Waveguides"

  filter_allpass input, delay*, scaler-feedback, scaler-feedforward
    "filter_allpass" or "moving average comb" is just like "filter_comb" but
    with an added feedforward term. If "scaler-feedback == 0", we get a
    moving average comb filter. If both scaler terms == 0, we get a pure
    delay line.

     y(n) = feedforward*x(n-1) + x(n-size-1) + feedback*y(n-size)

    cf. http://www.harmony-central.com/Effects/Articles/Reverb/allpass.html

  design_remez_fir filter_size, bands(2,b), desired_gain(b), type, [weight(b)]
    Calculates the optimal (in the Chebyshev/minimax sense) FIR filter
    impulse response given a set of band edges, the desired reponse on those
    bands, and the weight given to the error in those bands, using the
    Parks-McClellan exchange algorithm.

    The first argument sets the filter size: "design_remez_fir" returns as
    many coefficients as specified by this parameter.

    "bands" is a vector of band edge pairs (start - end), which specify the
    start and end of the bands in the filter specification. These must be
    non-overlapping and sorted in increasing order. Only values between 0 (0
    Hz) and 0.5 (the Nyquist frequency) are allowed.

    "des" specifies the desired gain in these bands.

    "weight" can be used to give each band a different weight. If absent, a
    vector of ones is used.

    "type" is any of the exported constants "BANDPASS", "DIFFERENTIATOR" or
    "HILBERT" and can be used to select various design types (use "BANDPASS"
    until this is documented ;)

  filter_src input, srate, [width], [sr-mod]
    Generic sampling rate conversion, implemented by convoluting "input"
    with a sinc function of size "width" (default when unspecified or zero:
    5).

    "srate" determines the input rate / output rate ratio, i.e. values > 1
    speed up, values < 1 slow down. Values < 0 are allowed and reverse the
    signal.

    If "sr_mod" is omitted, the size of the output piddle is calculcated as
    "length(input)/abs(srate)", e.g. it provides the full stretched or
    shrinked input signal.

    If "sr_mod" is specified it must be as large as the desired output, i.e.
    it's size determines the output size. Each value in "sr_mod" is added to
    "srate" at the given point in "time", so it can be used to "modulate"
    the sampling rate change.

     # create a sound effect in the style of "Forbidden Planet"
     $osc = 0.3 * gen_oscil $osc, 30 / $pdl->rate;
     $output = filter_src($input, 1, 0, $osc);

  filter_contrast_enhance input, enhancement
    Contrast-enhancement phase-modulates a sound file. It's like audio MSG.
    The actual algorithm is (applied to the normalised sound)
    "sin(input*pi/2 + (enhancement*sin(input*2*pi)))". The result is to
    brighten the sound, helping it cut through a huge mix.

  filter_granulate input, expansion, [option-hash], option => value...
    "filter_granulate" "granulates" the sound file file. It is the poor
    man's way to change the speed at which things happen in a recorded sound
    without changing the pitches. It works by slicing the input file into
    short pieces, then overlapping these slices to lengthen (or shorten) the
    result; this process is sometimes known as granular synthesis, and is
    similar to the "freeze" function. The duration of each slice is "length"
    -- the longer, the more like reverb the effect. The portion of the
    length (on a scale from 0 to 1.0) spent on each ramp (up or down) is
    "ramp". This can control the smoothness of the result of the overlaps.
    The more-or-less average time between successive segments is "hop". The
    accuracy at which we handle this hopping is set by the float "jitter" --
    if "jitter" is very small, you may get an annoying tremolo. The overall
    amplitude scaler on each segment is "scaler" -- this is used to try to
    to avoid overflows as we add all these zillions of segments together.
    "expansion" determines the input hop in relation to the output hop; an
    expansion-amount of 2.0 should more or less double the length of the
    original, whereas an expansion-amount of 1.0 should return something
    close to the original speed.

    The defaults for the arguments/options are:

     expansion      1.0
     length(*)      0.15
     scaler         0.6
     hop(*)         0.05
     ramp           0.4
     jitter(*)      0.5
     maxsize        infinity

    The parameters/options marked with (*) actually depend on the sampling
    rate, and are always multiplied by the "rate" attribute of the piddle
    internally. If the piddle lacks that attribute, 44100 is assumed. NOTE:
    This is different to most other filters, but should be ok since
    "filter_granulate" only makes sense for audiofiles.

  audiomix pos1, data1, pos2, data2, ...
    Generate a mix of all given piddles. The resulting piddle will contain
    the sum of all data-piddles at their respective positions, so some
    scaling will be necessary before or after the mixing operation (e.g.
    scale2short).

     # mix the sound gong1 at position 0, the sound bass5 at position 22100
     # and gong2 at position 44100. The resulting piddle will be large enough
     # to accomodate all the sounds:
     $mix = audiomix 0, $gong1, 44100, $gong2, 22100,  $gong2

  filter_center piddle
    Normalize the piddle so that it is centered around "y = 0" and has
    maximal amplitude of 1.

  scale2short piddle
    This method takes a sound in any format (preferably float or double) and
    scales it to fit into a signed short value, suitable for playback using
    "playudio" or similar functions.

  gen_fft_window size*, type, [$beta]
    Creates and returns a specific fft window. The "type" is any of the
    following. These are (case-insensitive) strings, so you might need to
    quote them.

     RECTANGULAR    just ones (the identity window)
     HANNING        0.50 - 0.50 * cos (0 .. 2pi)
     HAMMING        0.54 - 0.46 * cos (0 .. 2pi)
     WELCH          1 - (-1 .. 1) ** 2
     PARZEN         the triangle window
     BARTLETT       the symmetric triangle window
     BLACKMAN2      blackman-harris window of order 2
     BLACKMAN3      blackman-harris window of order 3
     BLACKMAN4      blackman-harris window of order 4
     EXPONENTIAL    the exponential window
     KAISER         the kaiser/bessel window (using the parameter C<beta>)
     CAUCHY         the cauchy window (using the parameter <beta>)
     POISSON        the poisson window (exponential using parameter C<beta>)
     RIEMANN        the riemann window (sinc)
     GAUSSIAN       the gaussian window of order C<beta>)
     TUKEY          the tukey window (C<beta> specifies how much of the window
                    consists of ones).
     COSCOS         the cosine-squared window (a partition of unity)
     SINC           same as RIEMANN
     HANN           same as HANNING (his name was Hann, not Hanning)

     LIST           this "type" is special in that it returns a list of all types

  cplx(2,n) = rfft real(n)
    Do a (complex fft) of "real" (extended to complex so that the imaginary
    part is zero), and return the complex fft result. This function tries to
    use PDL::FFTW (which is faster for large vectors) when available, and
    falls back to PDL::FFT, which is likely to return different phase signs
    (due to different kernel functions), so beware! In fact, since "rfft"
    has to shuffle the data when using PDL::FFT, the fallback is always
    slower.

    When using PDL::FFTW, a wisdom file ~/.pdl_wisdom is used and updated,
    if possible.

  real(n) = irfft cplx(2,n)
    The inverse transformation (see "rfft"). "irfft rfft $pdl == $pdl"
    always holds.

  spectrum data, [norm], [window], [beta]
    Returns the spectrum of a given pdl. If "norm" is absent (or "undef"),
    it returns the magnitude of the fft of "data". When "norm" == 1 (or "eq
    'NORM'", case-insensitive), it returns the magnitude, normalized to be
    between zero and one. If "norm" == 0 (or "eq 'dB'", case-insensitive),
    then it returns the magnitude in dB.

    "data" is multiplied with "window" (if not "undef") before calculating
    the fft, and usually contains a window created with "gen_fft_window"
    (using "beta"). If "window" is a string, it is handed over to
    "gen_fft_window" (together with the beta parameter) to create a window
    of suitable size.

    This function could be slightly faster.

  concat pdl, pdl...
    This is not really an audio-related function. It simply takes all
    piddles and concats them into a larger one. At the moment it only
    supports single-dimensional piddles and is implemented quite slowly
    using perl and data-copying, but that might change...

  filter_convolve
      Signature: (input(n); kernel(m); int fftsize(); [o]output(n))

    info not available

  rshift
      Signature: (x(n); int shift(); c(); [oca]y(n))

    Shift vector elements without wrap and fill the free space with a
    constant. Flows data back & forth, for values that overlap.

    Positive values shift right, negative values shift left.

  polynomial
      Signature: (coeffs(n); x(m); [o]out(m))

    evaluate the polynomial with coefficients "coeffs" at the position(s)
    "x". "coeffs[0]" is the constant term.

  linear_interpolate
      Signature: (x(); fx(n); fy(n); [o]y())

    Look up the ordinate "x" in the function given by "fx" and "fy" and
    return a linearly interpolated value (somewhat optimized for many
    lookups).

    "fx" specifies the ordinates (x-coordinates) of the function and most be
    sorted in increasing order. "fy" are the y-coordinates of the function
    in these points.

  bessi0
      Signature: (a(); [o]b())

    calculate the (approximate) modified bessel function of the first kind

  fast_sin
      Signature: (r(n); [o]s(n))

    fast sine function (inaccurate table lookup with ~12 bits precision)

AUTHOR
    Marc Lehmann <schmorp@schmorp.de>. The ideas were mostly taken from
    common lisp music (CLM), by Bill Schottstaedt "bil@ccrma.stanford.edu".
    I also borrowed many explanations (and references) from the clm docs and
    some code from clm.c. Highly inspiring!

SEE ALSO
    perl(1), PDL.

Revision:	1.3
Committed:	Tue Nov 8 18:56:06 2005 UTC (18 years, 6 months ago) by root
Branch:	MAIN
CVS Tags:	rel-1_1
Changes since 1.2:	+7 -3 lines
Log Message:	* empty log message *