Main Content


Convert magnitude to decibels



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


collapse all

Design a 3rd-order highpass Butterworth filter having a normalized 3-dB frequency of 0.5π 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));

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

Figure contains an axes object. The axes object contains an object of type line.

Repeat the computation using fvtool.


Figure Filter Visualization Tool - Magnitude Response (dB) contains an axes object and other objects of type uitoolbar, uimenu. The axes object with title Magnitude Response (dB) contains an object of type line.

Input Arguments

collapse all

Input array, specified as a scalar, vector, matrix, or N-D array. When y is nonscalar, mag2db is an element-wise operation.

Data Types: single | double

Output Arguments

collapse all

Magnitude measurements in decibels, returned as a scalar, vector, matrix, or N-D array of the same size as y.

See Also

| | |

Introduced in R2008a