calibrateMicrophone

Calibration factor for microphone

Since R2020a

Syntax

calibrationFactor = calibrateMicrophone(micRecording,fs,SPLreading)

calibrationFactor = calibrateMicrophone(micRecording,fs,SPLreading,Name,Value)

Description

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

Determine Microphone Calibration Factor

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 to your loudspeaker and simultaneously read a frame from your microphone.

• 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 = 1:numFrames
    audioOut = osc();
    audioIn = playRec(audioOut);
    write(buff,audioIn);
end
release(playRec);

SPL = 78.2; % read from physical SPL meter

micRecording = read(buff);

Compute the calibration factor for the microphone.

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

Calibrate Microphone Using Externally Generated Calibration Tone

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;

deviceReader = audioDeviceReader(fs);

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.

N = deviceReader.SamplesPerFrame;
while buff.NumUnreadSamples+N <= buff.Capacity
    audioIn = deviceReader();
    write(buff,audioIn);
end
release(deviceReader);

SPL = 77.7; % read from physical SPL meter

micRecording = read(buff);

Compute the calibration factor for the microphone.

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

Input Arguments

micRecording — Audio signal used to calibrate microphone

column vector | matrix

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

fs — Sample rate of microphone recording (Hz)

positive scalar

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

SPLreading — Sound pressure level reported from physical meter (dB)

scalar | vector

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 pairs of arguments as Name1=Value1,...,NameN=ValueN, where Name is the argument name and Value is the corresponding value. Name-value arguments must appear after other arguments, but the order of the pairs does not matter.

Before R2021a, use commas to separate each name and value, and enclose Name in quotes.

Example: calibrateMicrophone(micRecording,fs,SPLReading,'PressureReference',22)

PressureReference — Reference pressure (Pa)

20e-6 (default) | positive scalar

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

FrequencyWeighting — Frequency weighting used by physical meter

'A-weighting' (default) | 'C-weighting' | 'Z-weighting'

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

Data Types: char | string

Output Arguments

calibrationFactor — Microphone calibration factor

scalar | row vector

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:

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

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:

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

Extended Capabilities

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

Version History

Introduced in R2020a