# calibrateMicrophone

Calibration factor for microphone

## Description

example

calibrationFactor = calibrateMicrophone(micRecording,fs,SPLreading) returns the calibration factor for the microphone used to create micRecording.

calibrationFactor = calibrateMicrophone(micRecording,fs,SPLreading,Name,Value) specifies options using one or more Name,Value pair arguments.

Example: calibrationFactor = calibrateMicrophone(micRecording,fs,SPLreading,'FrequencyWeighting','Z-weighting') returns the calibration factor for an SPL reading that applies Z-weighting.

## Examples

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This diagram depicts the setup used in the example:

To run this example, you must connect a microphone and loudspeaker to a full-duplex sound card, and use an SPL meter to determine the true loudness level.

Create an audioOscillator object to generate a 1 kHz sine wave at a sample rate of 48 kHz.

fs = 48e3;
osc = audioOscillator("sine",1e3,"SampleRate",fs);

Create an audioPlayerRecorder object to write the sine wave to your loudspeaker and simultaneously read from your microphone.

playRec = audioPlayerRecorder(fs);

Create a dsp.AsyncBuffer object to store the audio recorded from your microphone. Specify the capacity of the buffer to hold 3 seconds worth of data.

dur = 3;
buff = dsp.AsyncBuffer(dur*fs);

In a loop, for three seconds:

• Generate a frame of a 1 kHz sinusoid.

• Write the frame acquired from your microphone to the buffer.

While the loop runs, note the true SPL measurement as reported from your SPL meter. Once complete, read the contents of the buffer object.

numFrames = dur*(fs/osc.SamplesPerFrame);
for ii = numFrames
audioOut = osc();
audioIn = playRec(audioOut);
write(buff,audioIn);
end

SPL = 78.2; % read from physical SPL meter

Compute the calibration factor for the microphone.

calibrationFactor = calibrateMicrophone(micRecording,playRec.SampleRate,SPL);

The diagram depicts the example setup and data flow.

To run this example, you must connect a microphone to your audio card, generate a 1 kHz tone using an external device, and use an SPL meter to determine the true loudness level.

Specify a 48 kHz sample rate for your audio device and a 3-second duration for acquiring audio. Create an audioDeviceReader object to read from your audio device.

fs = 48e3;
dur = 3;

Create a dsp.AsyncBuffer object to store the streamed audio.

buff = dsp.AsyncBuffer(dur*fs);

Start the 1 kHz test tone using an external loudspeaker. Then, in a loop, read from your audio device and then write the data to the buffer. While the loop runs, note the true SPL measurement as reported from your SPL meter. Once complete, read the contents of the buffer object.

tic
while toc < dur
write(buff,audioIn);
end

SPL = 77.7; % read from physical SPL meter

Compute the calibration factor for the microphone.

## Input Arguments

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Audio signal used to calibrate microphone, specified as a column vector (mono) or matrix of independent channels (stereo). micRecording must be acquired from the microphone you want to calibrate. The recording should consist of a 1 kHz test tone.

Data Types: single | double

Sample rate of microphone recording in Hz, specified as a positive scalar. The recommended sample rate for new recordings is 48 kHz.

Data Types: single | double

Sound pressure level reported from meter in dB, specified as a scalar or vector. If SPLreading is specified as a vector, it must have the same number of elements as columns in micRecording.

Data Types: single | double

### Name-Value Arguments

Specify optional comma-separated pairs of Name,Value arguments. Name is the argument name and Value is the corresponding value. Name must appear inside quotes. You can specify several name and value pair arguments in any order as Name1,Value1,...,NameN,ValueN.

Reference pressure for dB calculation in pascals, specified as a positive scalar. The default reference pressure (20 micropascals) is the common value for air.

Data Types: single | double

Frequency weighting used by physical meter, specified as 'A-weighting', 'C-weighting', or 'Z-weighting'.

Data Types: char | string

## Output Arguments

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Microphone calibration factor, returned as a scalar or row vector with the same number of elements as SPLreading.

Data Types: single | double

## Algorithms

To determine the calibration factor for a microphone, the calibrateMicrophone function uses:

• A calibration tone recorded from the microphone you want to calibrate.

• The sample rate used by your sound card for AD conversion.

• The known loudness, usually determined using a physical SPL meter.

• The frequency weighting used by your physical SPL meter.

• The atmospheric pressure at the recording location.

The diagram indicates a typical physical setup and the locations of required information.

The calibrationFactor is set according to the equation:

$\text{CalibrationFactor}=\frac{{10}^{\left(\left(\text{SPLreading}-k\right)/20\right)}}{\mathrm{rms}\left(\text{x}\right)}$

where x is the microphone recording passed through the weighting filter specified in the FrequencyWeighting argument. k is 1 pascal relative to the PressureReference calculated in dB:

$k=20{\mathrm{log}}_{10}\left(\frac{1}{\text{PressureReference}}\right).$