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
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
|
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN"
"http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">
<html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en" lang="en">
<head>
<title>TAP-plugins</title>
<meta name="generator" content="GNU Emacs 21.2.1">
<meta http-equiv="Content-Type" content="text/html;
charset=iso-8859-1">
<meta name="description" content="Tom's Audio Processing plugins for
audio engineering on the Linux platform.">
<meta name="keywords" content="TAP-plugins TAP Reverb Editor
Reverberator Equalizer EQ Vibrato Tremolo Echo Tom Szilagyi LADSPA
JACK Plugin Linux Audio">
<meta name="author" content="Tom Szilagyi">
</head>
<body bgcolor=#ffffff>
<table cellpadding="5" cellspacing="0" border="0" bgcolor=#ffffc0
width="100%">
<tr><td>
<font size="+2" color=#004060><b>TAP</b>-plugins</font><br>
<font color=#004060>Tom's Audio Processing plugins</font><br>
<font size="-1" color=#004060><i>for audio engineering on the Linux
platform</i></font>
</td><td>
<center>
<a href="../index.html">[ Home ]</a>
<a href="../ladspa.html">[ LADSPA plugins ]</a>
<a href="../reverbed.html">[ TAP Reverb Editor ]</a>
</center>
<hr>
<center>
<a href="releases.html">[ Releases ]</a>
<a href="general.html">[ General Info ]</a>
<a href="manuals.html">[ Plugin Manuals ]</a>
</center>
</td></tr>
</table>
<blockquote>
<a href="autopan.html">[ TAP AutoPanner ]</a>
<a href="chorusflanger.html">[ TAP Chorus/Flanger ]</a>
<a href="deesser.html">[ TAP DeEsser ]</a>
<a href="dynamics.html">[ TAP Dynamics (Mono & Stereo) ]</a>
<a href="eq.html">[ TAP Equalizer and TAP Equalizer/BW ]</a>
<a href="doubler.html">[ TAP Fractal Doubler ]</a>
<a href="pinknoise.html">[ TAP Pink/Fractal Noise ]</a>
<a href="pitch.html">[ TAP Pitch Shifter ]</a>
<a href="reflector.html">[ TAP Reflector ]</a>
<a href="reverb.html">[ TAP Reverberator ]</a>
<a href="rotspeak.html">[ TAP Rotary Speaker ]</a>
<a href="limiter.html">[ TAP Scaling Limiter ]</a>
<a href="sigmoid.html">[ TAP Sigmoid Booster ]</a>
<a href="echo.html">[ TAP Stereo Echo ]</a>
<a href="tremolo.html">[ TAP Tremolo ]</a>
<a href="tubewarmth.html">[ TAP TubeWarmth ]</a>
<a href="vibrato.html">[ TAP Vibrato ]</a>
</blockquote>
<h2>TAP Sigmoid Booster</h2>
<img src="tap_sigmoid.png" alt="[TAP Sigmoid Booster GUI as shown in Ardour]">
<p>
This plugin applies a time-invariant nonlinear amplitude transfer
function to the signal. Depending on the signal and the plugin
settings, various related effects (compression, soft limiting,
emulation of tape saturation, mild distortion) can be achieved.
</p>
<h3>General information</h3>
<table cellspacing="0" cellpadding="5" border="1">
<tr><th align="left">Unique ID</th><td>2157</td>
<tr><th align="left">I/O ports</th><td>1 input / 1 output</td>
<tr><th align="left">CPU usage (44.1 kHz)</th><td>0.7%</td>
<tr><th align="left">CPU usage (96 kHz)</th><td>2.1%</td>
<tr><th align="left">Hard RT Capable</th><td>Yes</td></tr>
<tr><th align="left">In-place operation</th><td>Supported</td>
<tr><th align="left">run_adding() function</th><td>Provided</td>
</table>
<h3>Usage tips</h3>
<p>
Given an input sample value of <i>x</i>, the plugin yields an output
sample value of <i>y(x)</i> according to the transfer function
</p>
<img src="tap_sigmoid_equation.png" alt="Equation of the transfer characteristics of
the plugin">
<p>
A plot of this function on a linear scale (red), compared to the
zero-gain identity transfer function (green):
</p>
<img src="tap_sigmoid_char_lin.png" alt="Transfer characteristics of
the plugin, linear scaled">
<p>
This curve resembles the saturation characteristics of magnetic
recording tape. Therefore, this effect results in compression of
louder portions of the input signal, a "hardening up" of the sound
(try it on kick and snare drums), and (when fed with a higher level
input signal) harmonic distortion consisting mainly of odd harmonics.
</p>
<p>
Let's see how this curve looks like on a logarithmical scale:
</p>
<img src="tap_sigmoid_char_db.png" alt="Transfer characteristics of
the plugin, log scaled">
<p>
As you can see, signals below -12 dB get amplified by about 8 dB's in
a fairly linear manner. Higher levels receive a constantly decreasing
amount of gain, resulting in no extra gain at 0 dB. Although not shown
on the above plot, the curve continues horizontally to the right,
meaning that complete saturation occurs at 0 dB.
</p>
<p>
The <i>Pre Gain</i> control scales the input signal before the
transfer function is applied to it. For low level input, you may want
to increase the input level to reach the nonlinear section of the
curve. For loud input signals, you will often have to decrease it to
reduce (or completely eliminate) the amount of audible distortion.
</p>
<p>
The <i>Post Gain</i> can be used to adjust the output gain of the
plugin.
</p>
<h3>Summary of user controls</h3>
<table cellspacing="0" cellpadding="5" border="1">
<tr><th>name</th><th>min. value</th><th>default value</th><th>max. value</th></tr>
<tr align="center"><td>Pre Gain [dB]</td>
<td>-90</td>
<td>0</td>
<td>20</td></tr>
<tr align="center"><td>Post Gain [dB]</td>
<td>-90</td>
<td>0</td>
<td>20</td></tr>
</table>
<h3>Notes</h3>
<p>
About the name of the plugin: it is "Sigmoid" because the transfer
function has been derived from the sigmoid function commonly used
in cells of neural networks as a nonlinear saturating function.
</p>
</body></html>
|
