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Helike 1.0 UA-E3010 | User manual
Released in November 2020, updated in June 2022
USound GmbH | www.usound.com | sales@usound.com
11.2.
ACOUSTIC CANCELLATION ON LEFT CHANNEL IN A TWO-
WAY SPEAKER SYSTEM
Due to a polarity inversion implemented in the connection of the DAC left channels (woofer and tweeter), it
is possible that acoustic cancellation occurs if Helike 1.0 UA-E3010 is used as a source for a stereo speaker
setup. To avoid it, the woofer speaker connection can be inverted.
11.3.
EQUALIZATION FILTER IMPLEMENTATION EXAMPLE
The following example shows how a set of biquad filter coefficients can be generated and copied into a
Helike 1.0 UA-E3010 configuration file. This method can be used to tune the acoustic response of speakers
connected to Helike 1.0 UA-E3010.
11.3.1.
OPEN SAMPLE.JSON FILE
Download the sample.json file from
https://github.com/usound-tech/audio_device_configuration
. Rename
the file if desired and open it in a text editor.
11.3.2.
GENERATE COEFFICIENTS
online tool and configure a filter. For this example, a low pass filter with a cutoff
frequency of 2kHz is used. Select a sampling rate of 48 kHz.
11.3.3.
COPY COEFFICIENTS TO .JSON FILE
Copy the coefficients generated by the tool to the Helike 1.0 UA-E3010 configuration file. Notice that in the
earlevel tool, the feedforward coefficients are designated as a0 through a2, and the feedback coefficients
are designated as b1 and b2. In Helike 1.0 UA-E3010 the designation is reversed. Furthermore, earlevel
uses a difference equation with negative signs before the feedback coefficients:
y[n] = a0 * x[n] + a1 * x[n-1] + a2 * x[n-2]
–
b1 * y[n-1]
–
b2 * y[n-2]
The Helike 1.0 UA-E3010 difference equation is as follows:
y[n] = b0 * x[n] + b1 * x[n-1] + b2 * x[n-2] + a1 * y[n-1] + a2 * y[n-2]
This means that the coefficients marked orange in Figure 20 (a0-a2 in earelvel) need to be copied to the
correct positions in the Helike 1.0 UA-E3010 configuration (b0-b2) and the coefficients marked yellow (b1
and b2 in earlevel) need to be copied to the positions a1 and a2 in the Helike 1.0 UA-E3010 configuration.
Since a different sign is used for the feedback coefficients, the two feedback coefficients generated by the
earlevel tool, also need to be negated for the use in the Helike 1.0 UA-E3010 configuration file.