AES17 - Level-dependent logarithmic gain (AKA Linearity Test)

Started by Tranquility Bass, September 25, 2020, 06:34:20 PM

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Tranquility Bass

Level-dependent logarithmic gain
Applies to: EUTs with analogue or digital inputs and analogue or digital outputs.

Aim: To measure the change in gain of the EUT with signal amplitude, sometimes called 'deviation
from level linearity'.

A 997Hz sinusoidal stimulus is applied at -5dBFS. The output of the EUT is measured after passing
through a 1/3 octave 997Hz band-pass filter. The gain of the EUT is calculated as being the ratio of its
output amplitude to its input amplitude. The narrow-band noise floor of the EUT is also measured
using the same band-pass filter, but with the stimulus muted.
The stimulus is reapplied, and its amplitude is then reduced in 5dB steps, until it is within 5dB of the
measured narrow-band noise floor, noting the output amplitude at each step and calculating the
inferred EUT gain. The results are graphed for each channel, with relativity to the gain measured at â€"
5dBFS expressed in dB, as a function of the applied amplitude. At the end of the test, a worst-case
gain deviation (in dB) is also reported for each channel.
When the A/D and D/A portions are available separately, this test should be repeated for each section

The Ultimate Preamplifier exhibits exception linearity all of the way down to -130dBFS yielding at least 22 bits of resolution !


Tranquility Bass

-5dBFS to -120dBFS range matches testing done by ASR

AES17 - Level-dependent logarithmic-gain.png

-5dBFS to -140dBFS full range AES17 test

AES17 - Level-dependent logarithmic-gain (-5  to -140dBFS).png