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Convert energy or power measurements to decibels


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


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).


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Express a unit voltage in decibels. Assume that the resistance is 2 ohms. Compare the answer to the definition, .

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

   -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 = 

   -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

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

Data Types: single | double
Complex Number Support: Yes

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

Data Types: char

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

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

  • If x contains voltage measurements, then dboutput is 10log10(|x|2/R).

  • If the input x contains power measurements, then dboutput is 10log10x.

See Also

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Introduced in R2011b

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