code>c</code> of the parameter must only have one letter to be well interpreted in the slider name <code>"volume %c[style:knob]"</code>:</p>
<!-- faust-run -->
<div class="faust-run"><img src="exfaust13/exfaust13.svg" class="mx-auto d-block">
<faust-editor><!--

mute = *(1-checkbox("mute"));
monoamp(c) = *(vslider("volume %c[style:knob]", 0.1, 0, 1, 0.01)) : mute;
stereoamp = hgroup("Marshall", monoamp(0), monoamp(1));

process = stereoamp;

--></faust-editor>
<br>
</div>
<!-- /faust-run -->

<h3 id="exampl