db

Convert energy or power measurements to decibels

Syntax

dboutput = db(x)

dboutput = db(x,SignalType)

dboutput = db(x,R)

dboutput = db(x,'voltage',R)

Description

dboutput = db(x) converts the elements of x to decibels (dB). This syntax assumes that x contains voltage measurements across a resistance of 1 Ω.

dboutput = db(x,SignalType) specifies the signal type represented by the elements of x as either 'voltage' or 'power'.

dboutput = db(x,R) specifies the resistance, R, for voltage measurements.

dboutput = db(x,'voltage',R) is equivalent to db(x,R).

Examples

Decibels from Voltage and Power

Express a unit voltage in decibels. Assume that the resistance is 2 ohms. Compare the answer to the definition, $$10{\log }_{10}\frac{1}{2}$$.

V = 1;
R = 2;
dboutput = db(V,2);
compvoltage = [dboutput 10*log10(1/2)]

compvoltage = 1×2

   -3.0103   -3.0103

Convert a vector of power measurements to decibels. Compare the answer to the result of using the definition.

rng default
X = abs(rand(10,1));
dboutput = db(X,'power');
comppower = [dboutput 10*log10(X)]

comppower = 10×2

   -0.8899   -0.8899
   -0.4297   -0.4297
   -8.9624   -8.9624
   -0.3935   -0.3935
   -1.9904   -1.9904
  -10.1082  -10.1082
   -5.5518   -5.5518
   -2.6211   -2.6211
   -0.1886   -0.1886
   -0.1552   -0.1552

Input Arguments

x — Signal measurements

scalar | vector | matrix | N-D array

Signal measurements, specified as a scalar, vector, matrix, or N-D array.

Data Types: single | double
Complex Number Support: Yes

SignalType — Type of signal measurements

'voltage' (default) | 'power'

Type of signal measurements, specified as either 'voltage' or 'power'. If you specify SignalType as 'power', then all elements of x must be nonnegative.

R — Resistive load

1 Ω (default) | positive scalar

Resistive load, specified as a positive scalar expressed in ohms. This argument is ignored if you specify SignalType as 'power'.

Data Types: single | double

Output Arguments

dboutput — Energy or power measurements in decibels

scalar | vector | matrix | N-D array

Energy or power measurements in decibels, returned as an array with the same dimensions as x.

• If x contains voltage measurements, then dboutput is $$10{\log }_{10}\left({\left|x\right|}^2/R\right).$$

• If the input x contains power measurements, then dboutput is $$10{\log }_{10}x.$$

Extended Capabilities

C/C++ Code Generation
Generate C and C++ code using MATLAB® Coder™.

Version History

Introduced in R2011b