!FIR - FIR filter, direct form !IIR - IIR filter, cascade of biquad sections !ALL - All-pole filter, direct formSubsequent records contain filter coefficients. Comment records ('!' in the first position of the record) can be interspersed amongst the data. Data records are free form, with data values separated by white space (blanks, tabs and newlines). Commas can also be used to separate data values, but only within records, i.e. a comma should not appear at the end of a record.
FIR filters are specified by the direct-form coefficients h[i],
N-1 -i
H(z) = SUM h[i] z .
i=0
IIR filters are implemented as the cascade of biquadratic filter sections, where each section has a z-transform,
h(i,0)*z^2 + h(i,1)*z + h(i,2)
H(i,z) = ------------------------------ .
z^2 + h(i,3)*z + h(i,4)
All-pole filters are specified by direct-form feeback coefficients,
1 N-1 -i
H(z) = ---- , where C(z) = SUM h[i] z .
C(z) i=0
For FIR filters, a sample rate change may be affected with interpolation and subsampling. Let Ir and Nsub be the interpolation and subsampling factors, respectively. Conceptually, the operations for FIR filters are as follows.
The initial filter alignment and the number of output samples can be specified with options. The filter alignment specifies the position of the filter relative to the input date for calculating the first output sample. For FIR filters, this alignment is relative to the increased rate input sequence. Specifically, let the number of samples in the input file be Nin. The input can be considered to be an array x(0),...,x(Nin-1). The increased rate sequence is xi(.), with xi(k*Ir)=x(k). The first output sample is calculated with the beginning of the impulse response of the filter aligned with xi(idoffs). The array xi(.) can be considered to be of length Nin*Ir; the first non-zero sample is xi(0)=x(0), the last non-zero sample is xi((Nin-1)*Ir). Conceptually, the impulse impulse response is moved in steps of Nsub to create the output samples.
The intent is that the output samples be a subset of the values the would be obtained if the infinite length sequence formed by padding out the input data on either end with zeros were to be filtered. To this end, the filter calculations need warm-up points, particularly for the case that the initial filter alignment is not at the beginning of the input data. For FIR filters, this is taken into account by reading previous input values into the filter memory. For IIR filters, previous outputs are also needed as warm-up points. If the initial alignment is near the beginning of the data, the IIR filter is run from the beginning of the data to generate the warm-up points. For larger alignment offsets, the IIR filter is backed up for a maximum of 1000 samples to provide the warm-up points.
If the initial filter alignment is not explicitly specified it is chosen to be zero, except for odd-length symmetric or anti-symmetric FIR filters for which it is is chosen to be (Ncof-1)/2. If the number of output samples is not explicitly set, it is chosen to be Ir*Nin/Nsub. For the case of Ir=1 and Nsub=1, this results in the same number of output samples as input samples. If the initial filter alignment, offs, is explicitly specified, the number of output samples is chosen to be (Ir*Nin-offs)/Nsub. This value can be overridden by explicitly setting the number of output samples.
"mu-law8" - 8-bit mu-law data "A-law8" - 8-bit A-law data "unsigned8" - offset-binary 8-bit integer data "integer8" - two's-complement 8-bit integer data "integer16" - two's-complement 16-bit integer data "float32" - 32-bit IEEE floating-point data "text" - text dataThe data formats available depend on the output file type. AFsp (Sun) audio files:
mu-law, A-law, 8-bit integer, 16-bit integer, floatRIFF WAVE files:
mu-law, A-law, offset-binary 8-bit integer, 16-bit integerAIFF-C audio files:
mu-law, A-law, 8-bit integer, 16-bit integerHeaderless files:
all data formats
"AFsp", "Sun" or "sun" - AFsp (Sun) audio file "WAVE" or "wave" - RIFF WAVE file "AIFF-C" - AIFF-C audio file "raw" or "raw_native" - Headerless file (native byte order) "raw_swap" - Headerless file (byte swapped) "raw_big-endian" - Headerless file (big-endian byte order) "raw_little-endian" - Headerless file (little-endian byte order)
For AFsp output files, the audio file header contains an information string.
Standard Header Information:
date:1994/01/25 19:19:39 UTC date
user:kabal@aldebaran user
program:FiltAudio program name
This information can be changed with the header information string which is
specified as one of the command line options. Structured information records
should adhere to the above format with a named field terminated by a colon,
followed by numeric data or text. Comments can follow as unstructured
information. For the purpose of this program, records are terminated by
newline characters. However in the header itself, the newline characters are
replaced by nulls. To place a newline character into the header, escape
the newline character by preceding it with a '\' character. If the first
character of the user supplied header information string is a newline
character, the header information string is appended to the standard header
information. If not, the user supplied header information string replaces
the standard header information.
"Format, Start, Sfreq, Swapb, Nchan, ScaleF"
"undefined" - Headerless files will be rejected "mu-law8" or "MU-LAW8" - 8-bit mu-law data "A-law8" or "A-LAW8" - 8-bit A-law data "unsigned8" or "UNSIGNED8" - offset-binary 8-bit integer data "integer8" or "INTEGER8" - two's-complement 8-bit integer data "integer16" or "INTEGER16" - two's-complement 16-bit integer data "float32" or "FLOAT32" - 32-bit floating-point data "text" or "TEXT" - text data
"native" - no byte swapping "little-endian" - file data is in little-endian byte order "big-endian" - file data is in big-endian byte order "swap" - swap the data bytes as the data is read
"undefined, 0, 8000., native, 1, 1.0"