manual/include/metering-in-ardour.html
Shamus Hammons dfec6899ef Initial cleanup of manual content.
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<h2>Introduction</h2>
<p>
An engineer reading and using audio level meters compares to a musician
reading or writing sheet-music. Just like there are virtuoso musicians
who can't read a single note, there are great sound-engineers who just
go by their ears and produce great mixes and masters without ever looking
at a single meter.
</p>
<p>
Yet, if you want to work in or with the broadcast industry, it is
usually unavoidable to use meters.
</p>
<p>
Audio level meters are very powerful tools that are useful in every
part of the entire production chain:
</p>
<ul>
<li>When tracking, meters are used to ensure that the input
signal does not <dfn>overload</dfn> and maintains reasonable
<dfn>headroom</dfn>.</li>
<li>Meters offer a <dfn>quick visual indication</dfn> of a
activity when working with a large number of tracks.</li>
<li>During mixing, meters provide an rough estimate of the
<dfn>loudness</dfn> of each track.</li>
<li>At the mastering stage, meters are used to check
compliance with upstream <dfn>level</dfn> and <dfn>loudness
standards</dfn> and to optimize the <dfn>loudness range</dfn>
for a given medium.</li>
</ul>
<h2>Meter Types</h2>
<p>
A general treatise on metering is beyond the scope of this
manual. It is a complex subject with a history&hellip;
For background information and further reading we recommend:
</p>
<ul>
<li><a href="http://www.digido.com/how-to-make-better-recordings-part-2.html">How To Make Better Recordings in the 21st Century&mdash;An Integrated Approach to Metering, Monitoring, and Leveling Practices</a> by Bob Katz. Has a good historic overview of meters and motivates the K-meter</li>
<li><a href="https://en.wikipedia.org/wiki/Peak_programme_meter#Table_of_characteristics">Wikipedia: Peak programme meter</a>&mdash;overview of meter types.</li>
<li>"Audio Metering: Measurements, Standards and Practice: Measurements, Standards and Practics", by Eddy Brixen. ISBN: 0240814673</li>
<li>"Art of Digital Audio", by John Watkinson. ISBN: 0240515870</li>
</ul>
<p>
There are different metering standards, most of which are available in Ardour. In short:
</p>
<dl>
<dt>Digital peak-meter</dt>
<dd>A <dfn>Digital Peak Meter</dfn> displays the absolute maximum signal
of the raw audio PCM signal (for a given time). It is commonly used when
tracking to make sure the recorded audio never clips. To that end, DPMs
are always calibrated to 0&nbsp;<abbr title="DeciBel Full
Scale">dBFS</abbr>, or the maximum level that can be represented digitally
in a given system. This value has no musical reason whatsoever and depends
only on the properties of the signal chain or target medium. There are
conventions for <dfn>fall-off-time</dfn> and <dfn>peak-hold</dfn>, but no
exact specifications.
<p>
Various conventions for DPM fall-off times and dBFS line-up level can be
chosen in <kbd class="menu">Edit &gt; Preferences &gt; GUI</kbd>.
</p>
</dd>
<dt>RMS meters</dt>
<dd>An <dfn><abbr title="Root Mean Square">RMS</abbr>-type meter</dfn>
is an averaging meter that looks at the energy in the signal. It
provides a general indication of loudness as perceived by humans. Ardour
features three RMS meters, all of which offer additonal peak indication.
<ul>
<li><dfn>K20</dfn>: A meter according to the K-system introduced by Bob
Katz, scale aligned to -20&nbsp;dBFS, rise/fall times and color schema
according to spec.</li>
<li><dfn>K14</dfn>: Same as K20 with scale aligned to -14&nbsp;dBFS.</li>
<li><dfn>K12</dfn>: Same as K20 with scale aligned to -12&nbsp;dBFS (since 3.5.143).</li>
<li><dfn>Peak + RMS</dfn>: standard RMS, customizable via
<kbd class="menu">Edit &gt; Preferences &gt; GUI &gt; Metering</kbd></li>
</ul>
</dd>
<dt>IEC PPMs</dt>
<dd><dfn><abbr title="International Electrontechnical Commission">IEC</abbr>-type
<abbr title="Peak Programme Meters">PPM</abbr>s</dfn> are a mix between DPMs and
RMS meters, created mainly for the purpose of
interoperability. Many national and institutional varieties exist (<abbr
title="European Broadcasting Union">EBU</abbr>, <abbr title="British Broadcasting
Corporation">BBC</abbr>, <abbr title="Deutsche Industrie-Norm">DIN</abbr>).
<p>
These loudness and metering standards provide a common point of
reference which is used by broadcasters in particular so that the
interchange of material is uniform across their sphere of influence,
regardless of the equipment used to play it back.
</p>
<p>
For home recording, there is no real need for this level of
interoperability, and these meters are only strictly required when
working in or with the broadcast industry. However, IEC-type meters have
certain characteristics (rise-time, ballistics) that make them useful
outside the context of broadcast.
</p>
<p>
Their specification is very exact, and consquently, there are no
customizable parameters.
</p>
</dd>
<dt>VU meters</dt>
<dd><dfn><abbr title="Volume Unit">VU</abbr> meters</dfn> are the dinosaurs (1939)
amongst the meters. They react very slowly, averaging out peaks.
Their specification is very strict (300ms rise-time, 1&ndash;1.5% overshoot,
flat frequency response). Ardour's VU meter adheres to that spec, but for
visual consistency it is displayed as a bar-graph rather than needle-style
(more below).
</dd>
</dl>
<h2>Ardour Specifics</h2>
<img class="right" src="/images/mixer-meter-context-menu.png" alt="mixer strip meter context menu" />
<p>
Meters are available in various places in ardour:
</p>
<ul>
<li>The mixer window features fixed height meters for each <dfn>channel strip</dfn>.</li>
<li>There are small (narrow) meters on each <dfn>track-header</dfn> in the editor window.</li>
<li>There are variable height meters in the <dfn>meterbridge window</dfn>.</li>
<li>Optionally, a fixed-size <dfn>master meter</dfn> can be displayed in the main toolbar.</li>
<li>Various other locations (<dfn>file import</dfn>, <dfn>sends</dfn>) have level-meters.</li>
</ul>
<p>
They all share the same configuration and color-theme which is available in
preferences and the theme-manager. Settings for the Peak and RMS+Peak meters
as well as VU meter standards are found in
<kbd class="menu">Edit &gt; Preferences &gt; GUI &gt; Metering</kbd>.
</p>
<p>
The type of meter and the <dfn>metering point</dfn> (the place in the signal chain
where the meter taps the signal) are configurable in the context menu of each meter.
Depending on the <kbd class="menu">Edit &gt; Preferences &gt; GUI &gt; Mixer
Strip</kbd> settings, the metering point is also accessible via a button in
each Mixer strip.
</p>
<img class="right" src="/images/meter-preferences.png" alt="" />
<p>
Regardless of meter type and standard the meter display will highlight red if
the signal on the given channel exceeds the configured peak threshold.
</p>
<p>
<kbd class="mouse">Left</kbd> on the peak-indicator button resets the
<dfn>peak-hold indicator</dfn> of a single channel.<br>
<kbd class="mod1 mouse">Left</kbd> resets a whole <dfn>group</dfn>, and<br/>
<kbd class="mod13 mouse">Left</kbd> resets all meters.
</p>
<h2>Overview of meter types</h2>
<p>
The figure on the left shows all available meter-types in Ardour 3.4 when fed with a
-18&nbsp;dBFS 1&nbsp;kHz sine wave.
</p>
<img class="right" style="max-width:45%;height:400px;" src="/images/needle-meters-18.png"
alt="Needle-style meters as external LV2 plugins" />
<img style="max-width:45%; height:400px" src="/images/meter-types-18.png"
alt="Bar-graph meters in Ardour" />
<p>
Due to layout concerns and consistent look&amp;feel all meters available in
Ardour itself are bar-graph type meters. Corresponding needle-style
meters&mdash;which take up more visual screen space&mdash;are available as
LV2 plugins (see image on the right):
<a href="https://github.com/x42/meters.lv2/">meters.lv2</a>.
</p>