sc/spectra [ Modules ]
NAME
spectra File: spectra.lsp Class Hierarchy: none (no classes defined) Version: 1.1.0 Project: slippery chicken (algorithmic composition) Purpose: Definition of the spectral data for piano and other instruments' notes. We'll use this data for the calculation of chord dissonance values in the chord class's calculate-dissonance method. Author: Michael Edwards: m@michael-edwards.org Creation date: July 27th 2015 $$ Last modified: 12:49:39 Thu Apr 18 2024 CEST SVN ID: $Id: spectra.lsp 5359 2015-07-24 20:53:22Z medward2 $
spectra/get-spectra-al [ Functions ]
[ Top ] [ spectra ] [ Functions ]
DATE
August 6th 2015, Edinburgh
DESCRIPTION
Create an assoc-list of spectral data by doing spectral analysis of all the sound files contained in a given directory. The aim is to extract the spectral data for harmonic partials, so we specifically look for ascending partials as close as possible to integer multiples of the sample sound file's fundamental frequency, as detected from the file name (see below). By default we average spectra over three separate readings at 300, 400, and 500 milliseconds. We do this in order to avoid spectral anomalies at any fixed point in any of the sound files, and of course to skip the onset transient and any inharmonicities therein. As the extensive analysis and processing here will take some computation time, in order to create our default spectral data for calculating a chord's dissonance or spectral centroid, I've performed the analysis on some of my local sample libraries. By then using the assoc-list method print-for-init I've copied the data into separate text files for reading into the +slippery-chicken-spectra+ global assoc-list and thus making these available to all slippery-chicken users. By modifying the examples at the bottom of this file, similar sample directories' spectral data could be added to this global.
ARGUMENTS
- the path to the samples directory. This should be something suitable for passing to the (directory) function so we'll need the extension of the sound files (see "*.wav" in the example below). - a function for processing the filenames (as a string, with no directory or extension e.g. "Stein-R(A0)-V(085)-dB(3478)-T(ML)-M(28)-P(2126-03-01)") in order to return the MIDI note number of the sample in that file. This whole approach is predicated on the assumption that sample file names will contain such pitch data. If that is not the case then get-spectra-al will be of no use. See the akoustik-piano-name and violin-ensemble-name functions below for examples.
OPTIONAL ARGUMENTS
Keyword arguments:
- :force-harmonics: whether to look for harmonic partials or not. If this
is nil then the returned spectra will be the strongest by amplitude
irrespective of their harmonicity. Default = t
- :harmonic-tolerance: the maximum deviation from the exact integer
partial. Default = 0.15
- :fftsize: The FFT window size for spectral analysis. Default = 4096
- :num-partials: the number of partials to identify and return.
Default = 12
- :id: The default ID for the resultant assoc-list. Default = 'spectra
- :analysis-points: The times in milliseconds at which to do the spectral
analysis and extract averages. If no averaging is necessary simply pass
one starting value as a list. Default = '(300 400 500)
RETURN VALUE
An assoc-list object whose keys are the MIDI note numbers associated with the spectral information of sample sound files. Each of these is in the form of a two element list: a list of fundamental scalers and a list of their amplitudes (normalised to 1.0).
EXAMPLE
(get-spectra-al "/path/to/samples/*.wav"
#'violin-ensemble-name :id 'violin-ensemble)
-->
ASSOC-LIST: warn-not-found T
CIRCULAR-SCLIST: current 0
SCLIST: sclist-length: 21, bounds-alert: T, copy: T
LINKED-NAMED-OBJECT: previous: NIL, this: NIL, next: NIL
NAMED-OBJECT: id: VIOLIN-ENSEMBLE, tag: NIL,
data: (
NAMED-OBJECT: id: 56, tag: NIL,
data: ((0.9889743194880222d0 2.0263850081954717d0 2.9990610385449314d0
4.024036707283989d0 5.032546599880615d0 6.013292183763263d0
7.0551329128964655d0 8.049590274637817d0 9.032029362954297d0
10.017427921485291d0 11.0461040956976d0 12.028523416637086d0)
(0.1748299156810844d0 0.6666103041159978d0 0.740572572283973d0
0.37090168062541756d0 0.2529382535743205d0 0.19313279338531672d0
0.290088638695093d0 0.20008736984066355d0 0.12280861470679348d0
0.15534581915388804d0 0.11772253740784348d0 0.11703054477270619d0))
...
SYNOPSIS
#+clm
(defun get-spectra-al (sample-dir name-fun
&key (force-harmonics t) (harmonic-tolerance 0.15)
(fftsize 4096) (num-partials 12) (id 'spectra)
;; millisec times of fft analysis
(analysis-points '(300 400 500)))