# 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'`.```

example

````dboutput = db(x,R)` specifies the resistance, `R`, for voltage measurements.```
````dboutput = db(x,'voltage',R)` is equivalent to `db(x,R)`.```

## Examples

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

```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

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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.

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 $10\text{ }\text{\hspace{0.17em}}{\mathrm{log}}_{10}\left({|x|}^{2}/R\right).$

• If the input `x` contains power measurements, then `dboutput` is $10\text{\hspace{0.17em}}{\mathrm{log}}_{10}x.$

## Version History

Introduced in R2011b