Low-, High-, Bandpass
Free programmable DSP-Filter

by Michael Keller, DL6iAK

DSPFIL runs as a free programmable LOW/HIGH/BANDPASS FIR filter in the audio range 0-4kHz and is programmable in the fly in real-time. Sampling rate is 8000 samples/s.

Lower/Upper-edge or width and center can be changed by the track bars. The graphic window shows the filter in frequency domain. The filter coefficients are calculated by a hanning windowed impulse response of a prototype Low Pass filter (sin(x)/x) followed by a frequency shift if necessary.

Changing the filter is done by moving the track bars. If track bar is activated, the arrow keys allow adjustment by one Hz increment. Any change will update the filter in real-time.

Care should be taken with the order (TAPS) of the filter, if slowly computers are used, he PC will may be hang up. I am using a PCI 128 sound blaster and an AMD 500 MHz K6 II, which runs the filter without problems up to 2300 taps, which yields very sharp filters. Nevertheless I limited TAPS to 2000, which is more than enough. Don't forget to disable any direct connect from MIC IN to the output (mixing console), only 'waves' should be activated as output source. The program is free for all non commercial purposes. I do not know, how the program is working on different hardware, just try it on your own risk.

Download dspfil.zip (202 KB)