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<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>
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<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 Scaling Limiter</h2>
<img src="tap_limiter.png" alt="[TAP Scaling Limiter GUI as shown in Ardour]">
<p>
You want to maximize the loudness of your master tracks. Your drummer
has the habit of playing with varying velocity. You want to squeeze
high transient spikes down into the bulk of the audio. You want a
limiter with transparent sound, but without distortion. This is for
you, then. The unique design of this innocent looking plugin results
in the ability to achieve signal level limiting <i>without audible
artifacts</i>.
</p>
<p>
Most limiters operate on the same basis as compressors: they monitor
the signal level, and when it gets above a threshold level they reduce
the gain on a momentary basis, resulting in an unpleasant "pumping"
effect. Or even worse, they chop the signal at the top. This plugin
actually <i>scales each half-cycle individually</i> down to a smaller
level so the peak is placed exactly at the limit level. This operation
(from zero-cross to zero-cross) results in an instantaneous blending
of peaks and transient spikes down into the bulk of the audio.
</p>
<h3>General information</h3>
<table cellspacing="0" cellpadding="5" border="1">
<tr><th align="left">Unique ID</th><td>2145</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>0.5% (see Notes)</td>
<tr><th align="left">CPU usage (96 kHz)</th><td>1.1% (see Notes)</td>
<tr><th align="left">Hard RT Capable</th><td>No</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>
Although this limiter is an exceptionally clean sounding one, it is
possible to introduce distortion by setting the limit level down into
the bulk of the audio. Only transients, drum beats and such things
(which "stand out" of the waveform) should be attacked. To illustrate
the optimal setting of this plugin, let's look at the following
waveforms (seemingly some unmastered rock music):
</p>
<img src="limiter1.png" alt="[Before/After Limiter Waveforms 1]">
<p>
As you can see, no signal gets above the limit level, so this plugin
acts as a brickwall limiter (with a compression ratio of inf:1 above
the limit level). But the two waveforms above sound exactly the
same! This is possible because transients last for a very short amount
of time, and despite their high level, they don't carry very much
energy compared to the bulk of the audio. Now let's take a closer look
at the same waveforms:
</p>
<img src="limiter2.png" alt="[Before/After Limiter Waveforms 2]">
<p>
As it can be seen, the waveform does not lose any of its details,
because half-cycles (from zero-cross to zero-cross) are individually
scaled down to the limit level (only those that have peaks above the
limit, of course).
</p>
<p>
When setting the "Limit Level", you should not go more than 7-8 dB
below the average peak level of the signal, which should be observed
via some peak-holding level meter. When using this plugin in Ardour,
this can be done very easily because the meters of the mixer strips
provide an excellent way to monitor exact peak values. Assuming an
unmastered mix of some rock music with drums, bass, guitars etc. you
can usually get down to the point where the Ardour level meter doesn't
move very much. Without hearing any distortion, of course. Because
high transients are squeezed down, the overall signal level can be
raised with the "Output Volume" control. Thus, this plugin is a very
effective way to transparently maximize the loudness of your mixes.
</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>Limit Level [dB]</td>
<td>-30</td>
<td>0</td>
<td>+20</td></tr>
<tr align="center"><td>Output Volume [dB]</td>
<td>-30</td>
<td>0</td>
<td>+20</td></tr>
<tr align="center"><td>latency</td>
<td colspan="3">latency time is 12.5 ms,<br>
value depends on sample rate</td>
</tr>
</table>
<h3>Notes</h3>
<p>
This plugin has a processing function that examines the input audio
signal and makes decisions based on sample values. So by definition,
this plugin cannot qualify as hard RT capable, although CPU demand
tends to be fairly constant during usage.
</p>
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