Signal Latency
Temporal lag introduced by finite impulse response filters during digital signal processing of sensor data. Constant fir group delay is a primary advantage for applications requiring linear phase response across a frequency spectrum. This delay is calculated by taking the derivative of the filter phase with respect to frequency.
In a linear phase filter, the delay is exactly half the number of taps in the filter sequence.
Phase Linearity
Maintaining the relative timing of different frequency components ensures that the shape of the waveform is preserved. Because fir group delay is independent of frequency, the filter does not distort the timing of complex signals. This characteristic is essential for seismic monitoring and medical imaging where the arrival time of a pulse carries information.
Designers often select fir filters over infinite impulse response alternatives specifically to gain this predictability.
Filter Characteristic
Total duration of the delay depends on the sampling rate and the length of the coefficient array. Increasing the number of taps to achieve a sharper cutoff also increases the fir group delay. This trade-off must be managed in real-time control systems where excessive latency can cause instability.
Hardware accelerators often handle the convolution to minimize the impact on the main processor.
Processing Effect
Compensation for the lag is often necessary when merging data from multiple sensors with different filter profiles. Subtracting the fir group delay from the time stamp of each sample allows for the alignment of disparate data streams. This synchronization is verified by measuring the response of the system to a known impulse.
Accurate timing is the result of careful filter design.
