How can I convert a .wav file to Pascals?

I have a 1 kHz tone, which is calibrated at 94 dB re. 20 uPa, and I am asked to calculate a scale factor which, by multiplying any point of the normalised amplitude, converts it to Pascals.

So far I have this, but it is wrong:

% Load the calibration audio file

[calibration_audio, calibration_fs] = audioread('calsig_1k_94dB.wav');

[unknown_audio, unknown_fs] = audioread('pianochord1scaled_corrected.wav');

% Calculate the number of samples corresponding to the first 50 ms

num_samples = round(0.05 * calibration_fs);

% Extract the first 50 ms of each signal

calibration_signal_original = calibration_audio(1:num_samples, 1); % Assuming a single-channel file

music_signal_original = unknown_audio(1:num_samples, 1); % Assuming a single-channel file

% Create a time vector for the x-axis

time_vector = (0:(num_samples - 1)) / calibration_fs;

% Create a figure to display the signals

figure;

subplot(2, 2, 1);

plot(time_vector, calibration_signal_original);

title('Calibration Signal (Original)');

xlabel('Time (s)');

ylabel('Amplitude');

% Define the scale factor for calibration signal in pascals

RMS = sqrt(calibration_audio/num_samples);

calibration_scale_factor = (20e-6)*(10^(RMS/20));

% Scale the calibration signal

calibration_signal_scaled = calibration_audio(1:num_samples, 1) * calibration_scale_factor;

First, I convert the normalised amplitude to dB RMS with the RMS variable (which I assume is wrong) and then apply the formula to convert RMS to Pascals.

Once I have the scale factor, I can also convert a .wav piano chord to Pascals as well.

[Mathieu NOE]

what is your question ??

Answer 1

[Mathieu NOE]

see here :

Matlab Spectrogram: How to convert the dB values to SPL? - MATLAB Answers - MATLAB Central (mathworks.com)

Answer 2

[Brahmadev]

Hi Ferran,

I understand that you would like to convert '.wav' data into ‘Pascals’.

For calculation of RMS value of the calibration signal, the following approach can be used:

RMS = sqrt(mean(calibration_signal_original.^2));

To find the 'calibration_scale_factor', you can refer to the following code:

% Calculate the scale factor of the calibration signal
reference_spl = 94; % dB re. 20 uPa
reference_pressure = 20e-6; % 20 microPascals
calibration_scale_factor  = 10^((reference_spl - 20 * log10(reference_pressure)) / 20);

Hence this new 'calibration_scale_factor' value can be used to convert the '.wav' values to ‘Pascals’ using:

audio_scaled = calibration_signal_original*calibration_scale_factor ;

I hope this provides you with relevant information on how to convert '.wav' values into 'Pascals'.

Best regards,

Brahmadev