first draft - towards documenting metering in ardour.

_manual/04_ardours-interface/06_meters.html

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+---
+layout: default
+title: Metering in Ardour
+---                        
+
+<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 virtuous 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 looking at a single meter.
+</p>
+<p>
+Yet, if you want to play along or work in broadcast-industry, it is mandatory to adhere to certain loudness-standards and it is usually unavoidable to use meters.
+</p>
+
+<p>
+Audio level meters are a very powerful tools that are useful in every part of the entire production chain:
+</p>
+
+<ul>
+	<li>When <strong>tracking</strong>, meters are used to ensure that the input signal does not peak and stays within reasonable limits.</li>
+	<li>Meters offer quick a visual indication of a signal being present on a given track or channel.</li>
+	<li>During <strong>mixing</strong>, meters provide an indication of the loudness of each track/channel and the loudness-range.</li>
+	<li>When <strong>mastering</strong>, meters can be used to check compliance to certain loudness-standards and to optimize the loudness-range for a given mixdown or medium.</li>
+</ul>
+
+<h2>Meter-Types</h2>
+<p>
+A general introduction on metering is beyond the scope of this manual. It is a complex subject with a history..
+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 - 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> - 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>
+
+<h3>Digital peak-meter</h3>
+<p>
+A DPM meter 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 does not clip or peak.
+</p>
+<p>
+These meters concentrate on the <em>medium</em> ie. digital numbers, and Analog/Digital converters.
+</p>
+<p>
+DPMs are always calibrated to 0dBFS (max. digital peak) which has no 'musical property' and is only medium related. There are also only conventions for fall-off-time and peak-hold but no exact specifications.
+</p>
+<p>
+Various conventions for DPM fall-off times and dBFS line-up level can be chosen in Edit &gt; Preferences &gt; GUI.
+</p>
+
+<h3>RMS meters</h3>
+<p>
+A RMS-type meter provide a general indication of loudness as perceived by humans.
+It emphasizes on the <em>message</em> as opposed to technical, medium related parameters.
+</p>
+<p>
+Ardour features three RMS meters all of which are dual peak + RMS meters
+</p>
+
+<ul>
+	<li><strong>K20</strong>: A meter according to the K-system, fixed dB alignment, rise/fall times and color-schema according to spec.</li>
+	<li><strong>K14</strong>: Same as K20 with a different dB alignment.</li>
+	<li><strong>peak + rms</strong>: standard RMS, obeys custom settings in ardour. Edit &gt; Preferences &gt; GUI &gt; Metering</li>
+</ul>
+
+<h3>IEC meter standards (EBU, BBC, DIN,..)</h3>
+<p>
+IEC type meters are a mix between DPM and RMS, created mainly for the purpose of interoperability.
+
+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 use to play it back.
+
+For the some home recording there is no real need for this level of interoperability and one does generally only need these meters when working in the broadcast industry.
+
+IEC-type also meters have certain characteristics (rise-time, ballistics) that are useful outside the context of broadcast.
+</p>
+
+<p>
+Their specification is very exact and as opposed to Ardour's DPM and RMS meters there are no customizable parameters.
+</p>
+
+<h3>VU meters</h3>
+<p>
+VU meters are the dinosaurs (1939) amongst the meters, they react very slowly, averaging out peaks.
+Their specification is very strict (300ms rise-time, 1 - 1.5% overshoot, flat frequency response).
+Ardour's VU meter adhere to that spec, but for visual consistency displays VU meters as bar-graph rather than needle-style (more below).
+</p>
+
+<h2>Ardour Specifics</h2>
+<p>
+Meters are available in various places in ardour:
+</p>
+<ul>
+	<li>The mixer window features fixed height meters with metric-area for each channel-strip.</li>
+	<li>There are small (narrow) meters on each track-header in the editor window.</li>
+	<li>There are variable height meters in the meterbridge window, also complete with tick-marks and metrics.</li>
+	<li>optionally, a fixed-size master meter can be displayed in the main toolbar.</li>
+	<li>Various other locations (file-import, effect send/return) 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 in  Edit &gt; Preferences &gt; GUI &gt; Metering.
+</p>
+
+<p>
+<img src="/ardour/manual/html/screenshots/meter-preferences.png" alt=""></p>
+</p>
+
+<p>
+The meter-type and the point where the meter taps-off the signal are configurable in the context-menu for each meter.
+Depending the Edit &gt; Preferences &gt; GUI &gt; Mixer Strip settings, the metering point is also available as button in the mixer-window.
+</p>
+
+<p>
+<img src="/ardour/manual/html/screenshots/mixer-meter-context-menu.png" alt="mixer strip meter context menu">
+</p>
+
+<p>
+Regardless of meter-type/standard the meter-display will highlight red if the signal on th given channel exceeds the configured peak threshold.
+</p>
+<p>
+To <strong>reset the meter peak-hold indicator</strong>, click on the peak-indicator button (ctrl + click to reset all in a group, ctrl + shift + click to reset all).
+</p>
+
+<h2>Overview of meter types</h2>
+
+<p>
+The following figure shows all available meter-types in Ardour 3.4 when fed with a -18dBFS 1kHz sine wave.
+</p>
+
+<p>
+<img src="/ardour/manual/html/screenshots/meter-types-18.png" alt=""></p>
+<p>
+
+<p>
+Due to layout concerns and consistent look&amp;feel all meters available in Ardour3 itself are bar-graph type meters.
+Corresponding needle-style meters - which take up more visual screen space - are available as LV2 plugins. Compare to meters above.
+</p>
+
+<p>
+<img src="/ardour/manual/html/screenshots/needle-meters-18.png" alt=""></p>
+<p>