1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
|
<refentry id="spectrum">
<indexterm id="IndexSpectrum"><primary>spectrum</primary></indexterm>
<refentryinfo><title>Spectral Processing:Non-Standard</title></refentryinfo>
<refmeta>
<refentrytitle>spectrum</refentrytitle>
</refmeta>
<refnamediv>
<refname>spectrum</refname>
<refpurpose>
Generate a constant-Q, exponentially-spaced DFT.
</refpurpose>
</refnamediv>
<refsect1>
<title>Description</title>
<para>
Generate a constant-Q, exponentially-spaced DFT across all octaves of a multiply-downsampled control or audio input signal.
</para>
</refsect1>
<refsect1>
<title>Syntax</title>
<synopsis>wsig <command>spectrum</command> xsig, iprd, iocts, ifrqa [, iq] [, ihann] [, idbout] \
[, idsprd] [, idsinrs]</synopsis>
</refsect1>
<refsect1>
<title>Initialization</title>
<para>
<emphasis>ihann</emphasis> (optional) -- apply a Hamming or Hanning window to the input. The default is 0 (Hamming window)
</para>
<para>
<emphasis>idbout</emphasis> (optional) -- coded conversion of the DFT output:
<itemizedlist>
<listitem>
<para>0 = magnitude</para>
</listitem>
<listitem>
<para>1 = dB</para>
</listitem>
<listitem>
<para>2 = mag squared</para>
</listitem>
<listitem>
<para>3 = root magnitude</para>
</listitem>
</itemizedlist>
The default value is 0 (magnitude).
</para>
<para>
<emphasis>idisprd</emphasis> (optional) -- if non-zero, display the composite downsampling buffer every <emphasis>idisprd</emphasis> seconds. The default value is 0 (no display).
</para>
<para>
<emphasis>idsines</emphasis> (optional) -- if non-zero, display the Hamming or Hanning windowed sinusoids used in DFT filtering. The default value is 0 (no sinusoid display).
</para>
</refsect1>
<refsect1>
<title>Performance</title>
<para>
This unit first puts signal <emphasis>asig</emphasis> or <emphasis>ksig</emphasis> through <emphasis>iocts</emphasis> of successive octave decimation and downsampling, and preserves a buffer of down-sampled values in each octave (optionally displayed as a composite buffer every <emphasis>idisprd</emphasis> seconds). Then at every <emphasis>iprd</emphasis> seconds, the preserved samples are passed through a filter bank (<emphasis>ifrqs</emphasis> parallel filters per octave, exponentially spaced, with frequency/bandwidth Q of <emphasis>iq</emphasis>), and the output magnitudes optionally converted (<emphasis>idbout </emphasis>) to produce a band-limited spectrum that can be read by other units.
</para>
<para>
The stages in this process are computationally intensive, and computation time varies directly with <emphasis>iocts</emphasis>, <emphasis>ifrqs</emphasis>, <emphasis>iq</emphasis>, and inversely with <emphasis>iprd</emphasis>. Settings of <emphasis>ifrqs</emphasis> = 12, <emphasis>iq</emphasis> = 10, <emphasis>idbout</emphasis> = 3, and <emphasis>iprd</emphasis> = .02 will normally be adequate, but experimentation is encouraged. <emphasis>ifrqs</emphasis> currently has a maximum of 120 divisions per octave. For audio input, the frequency bins are tuned to coincide with A440.
</para>
<para>
This unit produces a self-defining spectral datablock <emphasis>wsig</emphasis>, whose characteristics used (<emphasis>iprd</emphasis>, <emphasis>iocts</emphasis>, <emphasis>ifrqs</emphasis>, <emphasis>idbout</emphasis>) are passed via the data block itself to all derivative <emphasis>wsigs</emphasis>. There can be any number of spectrum units in an instrument or orchestra, but all <emphasis>wsig</emphasis> names must be unique.
</para>
</refsect1>
<refsect1>
<title>Examples</title>
<para>
<informalexample>
<programlisting>
asig <emphasis>in</emphasis> ; get external audio
wsig <emphasis>spectrum</emphasis> asig,.02,6,12,33,0,1,1 ; downsample in 6 octs & calc a 72 pt dft (Q 33, dB out) every 20 msecs
</programlisting>
</informalexample>
</para>
</refsect1>
</refentry>
|
