mag2db

Convert magnitude to decibels

Syntax

ydb = mag2db(y)

Description

ydb = mag2db(y) expresses in decibels (dB) the magnitude measurements specified in y. The relationship between magnitude and decibels is ydb = 20 log₁₀(y).

Examples

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Magnitude Response of a Highpass Filter

Open Live Script

Design a 3rd-order highpass Butterworth filter having a normalized 3-dB frequency of $0.5 π$ rad/sample. Compute its frequency response. Express the magnitude response in decibels and plot it.

[b,a] = butter(3,0.5,'high');
[h,w] = freqz(b,a);

dB = mag2db(abs(h));

plot(w/pi,dB)
xlabel('\omega / \pi')
ylabel('Magnitude (dB)')
ylim([-82 5])

Figure contains an axes object. The axes object with xlabel omega blank / blank pi, ylabel Magnitude (dB) contains an object of type line.

Repeat the computation using fvtool.

fvtool(b,a)

Figure Figure 1: Magnitude Response (dB) contains an axes object. The axes object with title Magnitude Response (dB), xlabel Normalized Frequency ( times pi blank r a d / s a m p l e ), ylabel Magnitude (dB) contains an object of type line.