dsp.DigitalFilter has been removed. Use
dsp.FIRFilter, dsp.BiquadFilter,
dsp.IIRFilter, or dsp.AllpoleFilter
instead.
For FIR filter structures, use dsp.FIRFilter.
For Biquad (SOS) structures, use dsp.BiquadFilter.
For non-SOS IIR filter structures, use dsp.IIRFilter.
For All pole structures, use dsp.AllpoleFilter.