Dorrough And Euphonix Metering Techniques - Euphonix System 5 Application Note

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Dorrough and Euphonix Metering Techniques

The Dorrough technical manual states, "The peak excursion and persistence amplitude are
equal under steady-state, sine wave conditions." Persistence amplitude refers to the method
by which Dorrough establishes their average value; it is not an RMS average. Why does a
Dorrough Loudness Meter show a zero average and zero peak for a sine wave? It has been
a convention in the audio industry to display a sine wave's peak and average values as 0 on a
VU meter. Remember, this is not the actual RMS average; it is just how the meter responds.
Dorrough has chosen to implement their averaging technique to yield this familiar result.
An anomaly arises, though, when a Dorrough meter measures a square wave (Figure 2).
It is clear from Figure 2 that the square wave's RMS average and peak values wave are
equal. A Dorrough meter presents a perplexing result: the peak level is 3 dB lower than the
average level.
Fortunately, there is a reasonable explanation for this! Dorrough depends on the audio
industry's penchant for using sine waves to make calibration measurements and designed
their meters accordingly; the square wave anomaly is considered an acceptable trade-off.
Furthermore, sine and square waves are generated signals that do not occur in nature; audio
signals are complex waveforms. Measuring pink noise, as well as audio signals, on a
System 5 meter and a Dorrough Loudness Meter produce the same levels.
Euphonix and Dorrough meters do have different displays. Euphonix uses the DBFS con-
vention with 0 at the top and negative values below. Dorrough uses 0 at the bottom and
positive values above. Both meters measure decibels. With a reference level of -20 dBFS
in System 5, pink noise measures around -12 dBFS peak and -20 dBFS average. The
Dorrough meter shows a peak value of +8 and an average level of 0. The difference between
peak and average values for both System 5 and Dorrough meters is the same.
For more information on metering, see
Then click Audio - Levels & Readings
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Square Wave
Figure 2 Square wave
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Rectified Square Wave
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Peak Level = 1
Avg Level = 1
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