I am trying to design a IIR lowpass filter with the Matlab filterbuilder function. The filter should be with a low order, but steep. So I decided to use an elliptic one. I am working with an audio signal, so my sampling rate is 48 kHz an the stopband should be around 15 kHz. I have generated the following filter:
IIR
order: 6
frequency constraints: passband edge and stopband edge
Fpass: 0.45
Fstop: 0.55
Magnitude constraints: Passband ripple
Apass: 1dB
Design method: elliptic
Structure: Direct Form II SOS
In the "Data Type" Tab I am not sure about the arithmetic.
I tried to use Fixed-point datatype, because I want to use this filter with Altera Quartus. After implementing the filter in Quartus there is no signal at the output. The input is a sinus-signal with 14 bits word length generated by an NCO and the output length should be 14 bits too.
I don't know how to set the parameters in the data type section in the Matlab filterbuilder.
Does Quartus interpret the signals as "fixed-point" ??
Thank you for help!
Tobias
