4 CHANNEL POWER AMP TA 4D
OPERATING INSTRUCTIONS
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P a g e
2.1.3 Special Highlights for the Signal Processing
A short impulse in an analog equalizer is extended in the time domain and creates in the output
stage of the equalizer a post-oscillation of the impulse response. On top of all this, the mass of the
driver creates an additional post-oscillation initiated by the same impulse. Combined together
these changes in signal-motiontiming at the output stage leaves little in common with the original
signal. KS Audio developed the FIR (Finite Impulse Response) filtering technology, called FIRTEC ®.
This technology removes any of the delay time distortion and handles the time domain as well as
the frequency response. The correction of the input signal is done immediately in the time domain,
through a mathematical convolution of the input signal and the impulse response of the digital
equalization filters. Conversely, traditional analog filter / equalizer technology tries to correct the
frequency response of the signal through various filter elements which degrades the original
impulse signal response. The new digital FIRTEC ® technology equalizes the signal immediately and
corrects it to exactly match the original impulse. This is a physical equalization of the frequency
response in volume and phase.
2.1.4 Crossover
In reality, the analog filtering process tries to correct the frequency response of the audio signal
through various filter elements and as a result, degrades the quality of the signal’s impulse
response. The FIRTEC ® technology digitally equalizes the input signal immediately and corrects the
actual impulse of the signal. This is a physical equalization of the frequency response in volume
and phase. The cross over is optimized to be linear for frequency and phase (Bessel Filter). In analog
systems, phase shifts exist in between crossover points which can produce a result of near
cancellation of the sound pressure between systems when running various speakers in parallel (2-
way / 3-way systems). The KS Audio FIRTEC ® technology is based on a combined Bessel filter and
Differential filter process to yield superior results. This means the high frequency response is the
result between the low pass filter and the input signal. In consequence the result is an optimal
addition between the high and the low frequency cross over points. Instead of a phase shift as
found in an analog cross-over, in the KS Audio digital process, the time domain of the low pass
signal is only considered, and the rest of the process follows this.
Importantly, the geometrical offset between the drivers is compensated for and the resulting
output is sample accurate to the input in the time domain. To assure the best possible equalization
of the entire system the FIR filters work with the entire signal path not just the individual frequency
range: the critical cross-over between high and mid frequency drivers are precisely corrected.
The measurements taken to program the FIR filters are taken using a completely finished speaker
enclosure so this measurement includes the characteristics of the speaker box itself. This operation
allows each speaker box to be measured and programmed individually in production as well as in
the final venue when the room acoustics are “built-in”, then the FIR filters can adjust for this as well.
A correct impulse response is the key to duplicating the audio image in terms of the depth, as well
as the correct orientation of the instruments in a room.
