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M-Pack
1: WAV file processing: MATLAB function reference
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| Version 1.2 |
Requires MATLAB
6.0 (R12) or later |
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Determines
the peak absolute value of each channel of the input
WAV file data. The file scan is performed chunk-by-chunk
to avoid the need for large RAM allocations when scanning
large files. Supports both WAVE_FORMAT_PCM and WAVE_FORMAT_EXTENSIBLE
multichannel uncompressed formats and any bit resolution
between 2 and 32 inclusive. |
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| File
format: |
m-file |
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Editable
source code:
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yes
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| Utilises
non-editable functions: |
no |
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Platform:
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PC/Windows
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| Required
MATLAB Toolboxes: |
none
(except core MATLAB) |
| Demo
version limitations: |
p-code
only (non-editable), 30 second WAV file length limit
(then silence) |
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PeakAmplitude
= wavpeakfind(InputWavFile);
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[PeakAmplitude,
PeakLocation]= wavpeakfind(InputWavFile); |
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[PeakAmplitude,
PeakLocation]= wavpeakfind(InputWavFile,... |
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Tolerance);
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[PeakAmplitude,
PeakLocation]= wavpeakfind(InputWavFile,... |
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Tolerance,Scaling);
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[PeakAmplitude,
PeakLocation]= wavpeakfind(InputWavFile,... |
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Tolerance,Scaling,ReadChunkSize);
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[PeakAmplitude,
PeakLocation]= wavpeakfind(InputWavFile,... |
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Tolerance,Scaling,ReadChunkSize,WaitbarActivate);
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| Inputs: |
| InputWavFile |
name of the input WAV file.
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| Tolerance |
Optional [default 0]: to be used in combination with
the PeakLocation
output option (see below).
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| Scaling |
Optional
argument [default 'full']. Describes the scaling law
applied when reading the input WAV file. Identical to
the scale
argument in wavin.
See wavin
for full range of options. |
| ReadChunkSize |
Optional
argument [default value 65536]. Represents the length
(in samples per channel) of each successive chunk
to be processed. Can have an arbitrary value, but
if too small, computational efficiency will be compromised
since the file I/O operations are relatively slow.
If too large, memory requirements may be excessive.
(Note: the value is overridden if the file length
happens to be smaller!)
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| WaitbarActivate |
Optional
argument. If the argument is present (even if empty),
the progress is displayed via a waitbar which can
be customized via the following optional fields:
- Handle
field (i.e. WaitbarActivate.Handle) the handle of
an externally-generated waitbar figure. If omitted
a new locally-generated waitbar is created (then
deleted at the end of the function)
- Label
field (i.e. WaitbarActivate.Label) string containing
the label of the waitbar
If
this input argument is omitted, no waitbar will be
used.
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| Note:
any of the following input arguments: Tolerance, ReadChunkSize,
WaitbarActivate, may be substituted by [ ] to force
their respective default value(s). |
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| Outputs: |
| PeakAmplitude |
Vector containing peak absolute values, one element
per channel.
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| PeakLocation |
Optional
argument: if specified, requires an additional scan
(slower!)
Cell array containing the location indices of the
peaks. One column of indices per channel.
Note:
each channel can have more than one location for its
peak since the peak may be repeated. The "Tolerance"
input argument specifies "how close" a given
value must be relative to the peak in order to be
included. For example, a Tolerance of 0 suggests that
only peaks of the same value (to floating point precision
will be included). A Tolerance value of 0.1 suggests
that all amplitudes that exceed 90% of the peak will
be included, etc.
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Inspect
the source code of this function for a demonstration
of how to use the wavin wavout
function in chunk-by-chunk mode.
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following examples are contained in the m-script file
entitled xmplwavpeakfind.m
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| Ex.1 |
Determine
the peak amplitudes of each channel of the 4-channel
WAV file '4channel.wav'
(assuming default 'full'
scale when reading -- which implicitly assumes that
the data is contained within +/-1 when transformed from
integer storage format) |
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PeakAmplitude
= wavpeakfind('4channel.wav') |
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0.6793
0.6781 0.7940 0.9699 |
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| Ex.2 |
Same
as above but with
'raw' scaling when reading (i.e. reads the integers
directly without transforming to floating-point): |
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PeakAmplitude
= wavpeakfind('4channel.wav',[],'raw') |
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22258
22219 26018 31783 |
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| Ex.3 |
Same
as Ex.1 but with a waitbar (activated by including the
5th input argument, even if empty). Also, for example,
override the default read chunk size with 1024 (thereby
slowing down the process, albeit with less RAM usage): |
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PeakAmplitude
= wavpeakfind('4channel.wav',[],[],1024,[]) |
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0.6793
0.6781 0.7940 0.9699 |
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| Ex.4 |
Same
as above but include the location output argument with
zero tolerance (i.e. determine location of exact peaks
only): |
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[PeakAmplitude,
PeakLocation] =
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wavpeakfind('4channel.wav',0,[],1024,[])
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PeakAmplitude
= |
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0.6793
0.6781 0.7940 0.9699 |
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PeakLocation
= |
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[7313]
[97324] [47715] [135889] |
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Plot
the results: |
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[y,fs]=wavin('4channel.wav');
plot(y); hold; |
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for
j=1:length(PeakLocation) |
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stem(PeakLocation{j},y(PeakLocation{j},j),'k.')
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end; |
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| Ex.5 |
Same
as above but include the location output argument with
5% tolerance (i.e. determine location of all points
within 5% of the exact peaks). |
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[PeakAmplitude,
PeakLocation] =
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wavpeakfind('4channel.wav',0.05);
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Plot
the results, noting the multiple sub-peaks within 5%
of the exact peaks. |
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