manual/include/metering-in-ardour.html

<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>