AS3460
ALC Characterization
Demo Kit Manual
• PUBLIC
UG000480
• v3-00 • 2021-Nov-08
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│ 113
12
ALC Characterization
The characterization process for an ALC headphone is slightly more complex compared to standard
ANC, since characterization has to be done for multiple different acoustic leakage conditions. Acoustic
leakage describes the fit of the earbud inside the listener’s ear. If the earbud sits tightly inside the ear,
the leakage is very low and if it sits loosely inside the ear then the leakage is high. The ALC algorithm
running on AS3460 will adapt the ANC filters in real time to compensate for this leakage to give
constant ANC performance for all acoustic leakage conditions.
It is necessary to characterize 5 different leakage conditions to cover the whole acoustic leakage
range that can occur when people wear the headphones.
12.1
Characterization Methods
There are two different methods to do the characterization.
Method 1:
Characterization is done on the Leaky Measurement Adapter (LMU)
Method 2:
Characterization is done on the human ear
12.1.1
Method 1: LMU
For In-ear type earbuds (leaky and silicone ear-tip type)
ams
has developed the LMU, which allows
characterization under different acoustic leakage conditions. The amount of leakage can be adjusted
by the user by placing spacers of different thickness (
1
) in between the earbud holder (
2
) and the rest
of the adapter. The LMU was optimized to behave very similar to a real human ear acoustically.
Figure 125:
Leaky Measurement Adapter (LMU) Measurement
