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The capability of averaging measurement data adds complexity to the user interface, but
averaging is sometimes essential to arrive at valid end results. Note that averaging takes
place on the level of the individualy measured data points along the decay curve (so not just
across individually measured reverberation times).
In the table on the measurement details screen, a column is shown that indicates the status
(reliability) of the current average measurement for the corresponding frequency:
•
A green checkmark indicates a healthy, reliable measurement. The
RT60 measurement data may be presumed accurate with a margin of error
of at most 0.1 seconds.
•
A yellow exclamation point indicates that the measurement accuracy
cannot be guaranteed. This may have various causes. For example, the
signal-to-noise ratio may be insufficient (not enough dynamic range
between the steady-state noise signal and the noise floor with the noise
source switched off). This may also happen if the signal fluctuates more
than expected for a given frequency band and the resulting linear decay fit
is poor.
•
A red cross indicates that the result is statistically deemed unreliable.
In order to obtain a reliable result in the corresponding frequency band,
averaging across more individual measurements (adding to the overall
measurement time) is needed. If the red cross persists upon averaging
across multiple measurements, disregard the corresponding frequency
band or repeat the entire measurement series.
It is good practice (and a formal requirement for many applications) to average across as
many measurements as needed to obtain a green cross next to all relevant frequency bands.
Never rely on results from RT60 measurements until you have checked the re-
ported status per individual frequency band. Note that in some rooms it may
be difficult, if not impossible, to obtain reliable results for the lowest frequency
bands.
Please take note of the following practical tips and pointers for RT60 measurements:
•
Do not place the measurement microphone and noise source too close to
each other; if possible, estimate the reverberation radius in the room, and
make sure that the microphone is as far outside the speaker's reverberation
radius as possible.
•
Make sure that your noise source is capable of producing levels far above
the ambient noise floor in the room, and above the electronic noise floor of
the device. Ambient levels of 90 dB(A) and higher are often needed. The
SNR must be at least 50 dB in all relevant frequency bands.
24
VOX -01 Operating Manual
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