Cutoff frequency in graph

Hello, I have this code corresponding to a chebyshev filter and the graph that matlab returns to me. The question is, is the upper cutoff frequency that of the green line (0.7 on the y-axis) or that of the black line (0.25 on the x-axis)?

Answer 1

[Chunru]

For cheby filter, the cut-off frequency is the edge frequency at which the magnitude response of the filter is –Rp (passband ripple) decibels. In your plot, it should be somewhere between the black and blue.

[Juan Chehin]

3 dB is specified

[Chunru]

doc cheby1: Wn is at the response of -Rp.

[Chunru]

From documentation:

[b,a] = cheby1(n,Rp,Wp)

Wp — Passband edge frequency

scalar | two-element vector

Passband edge frequency, specified as a scalar or a two-element vector. The passband edge frequency is the frequency at which the magnitude response of the filter is –Rp decibels. Smaller values of passband ripple, Rp, result in wider transition bands.