DD4WH
Well-known member
Bob Larkin provided very nice code for an Audio Equalizer (https://forum.pjrc.com/threads/60928-Audio-Equalizer-using-FIR?highlight=audio+equalizer), which I implemented as a 9-band graphical EQ in the latest version of the Teensy Convolution SDR.
I was always a little unhappy with the built-in five-band-EQ of the SGTL5000 codec, because my impression was, it did not accurately separate the frequencies (Adjusting Bass also impacted Mids etc.). This seems much better now with the FIR-based EQ by Bob. But it also takes a lot more CPU power.
We have to experiment with several parametres:
* menu: adjustable dB response for 9 bands (separate responses for wideband FM and the other modes) --> a nice feature is the graphical display of the frequency response, I tried to scale the frequency-axis logarithmically
* hardcoded (see lines 1918ff): 60dB stopband attenuation
* hardcoded: centre frequencies for the nine bands
* hardcoded: number of FIR coefficients: at the moment 199 taps for the T4 and 69 taps for the T3.6
Please feel free to test and report any bugs.
I was always a little unhappy with the built-in five-band-EQ of the SGTL5000 codec, because my impression was, it did not accurately separate the frequencies (Adjusting Bass also impacted Mids etc.). This seems much better now with the FIR-based EQ by Bob. But it also takes a lot more CPU power.
We have to experiment with several parametres:
* menu: adjustable dB response for 9 bands (separate responses for wideband FM and the other modes) --> a nice feature is the graphical display of the frequency response, I tried to scale the frequency-axis logarithmically
* hardcoded (see lines 1918ff): 60dB stopband attenuation
* hardcoded: centre frequencies for the nine bands
* hardcoded: number of FIR coefficients: at the moment 199 taps for the T4 and 69 taps for the T3.6
Please feel free to test and report any bugs.