I have two xxx.wav input files recorded for 30 seconds in noise lab at different conditions with fs 44,100 need to plot normalized frequency Vs dB in one plot

I have two .wav input files recorded for 30 seconds with fs 44,100 each . I want a matlab code for frequency analysis plot in one panel to compare two wav file inputs

Answer 1

[Walter Roberson]

Read the files. Isolate a single channel on each. If they are different frequencies, resample to a common frequency. If one is shorter than the other, truncate the longer. Subtract the mean of each signal from the signal.

Now fft each signal. plot() the real() or imag() or abs() of the first result. Use "hold on" . plot() the real() or imag() or abs() of the second result. Label the plot.

[Nega Ejjigu]

The record was done using sound meter app. My goal is I have one shielding cage built so to compare two records of sound waves in noisy lab. One record inside the cage and the second outside the cage for 30 seconds record for each then to see frequency domain plot in one panel. Iam not sure here if they are different frequencies. So I would be very glad if I can get a code that reads two input .wav files and executes normalized frequency againist dB plot for both inputs in one plot.

I got one matlab code from the forum randomly :

clear, clc, close all
[x,fs] =audioread('recordUnshield16bit.wav');  

x = x(:, 1); %Create Vector                       
xlen = length(x);

t = (0:length(x)-1)/fs;
wlen = 1024;                        
nfft = 4*wlen;                      
hop = wlen/4;      

TimeRes = wlen/fs;                  
FreqRes = 2*fs/wlen;               
TimeResGrid = hop/fs;               
FreqResGrid = fs/nfft;   

w1 = hann(wlen, 'periodic');
[~, fS, tS, PSD] = spectrogram(x, w1, wlen-hop, nfft, fs);
Samp = 20*log10(sqrt(PSD.*enbw(w1, fs))*sqrt(2));

w2 = hann(xlen, 'periodic');
[PS, fX] = periodogram(x, w2, nfft, fs, 'power');
Xamp = 20*log10(sqrt(PS)*sqrt(2));

grid on

subplot(3, 3, [4 7])
plot(fX, Xamp)
%grid on
xlim([0 max(fX)])
%ylim([min(Xamp)-10 max(Xamp)+10])
view(0, 90)
set(gca, 'FontName', 'Times New Roman', 'FontSize', 12)
xlabel('Frequency, Hz')
ylabel('Magnitude, dB')
colormap bone

Can anybody customize this code for my case? ( to read two wav inputs then to plot in one panel normalized frequency vs dB)

Thanks in advance for help

[Walter Roberson]

If you want spectrogram() or periodogram(), then NO: those functions always clear the axes, if I recall correctly, because both of them are creating GUIs rather than just plots.

However, if you are just looking to plot your fft in db then see https://www.mathworks.com/matlabcentral/answers/321635-fft-in-db-scale#answer_251729 for how to make the coordinate transformation -- and other than that, the key is "hold on".

[Nega Ejjigu]

just i want to compare them in one plot. comparing using FFT in dB also works for me. Wondering still if I can get a code that can read two inputs and display in one plot using FFT in dB

Thanks

[Walter Roberson]

load handel
sig1 = y;
load laughter
sig2 = y;
minlen = min(length(sig1), length(sig2));
sig1 = sig1(1:minlen);
sig2 = sig2(1:minlen);

sig1 = sig1 - mean(sig1);
sig2 = sig2 - mean(sig2);

ff1 = fftshift(fft(sig1));
ff2 = fftshift(fft(sig2));
db1 = mag2db(ff1);
db2 = mag2db(ff2);
x = linspace(-Fs/2, Fs/2, length(db1));
bnd = 1000*floor(Fs/2000);

plot(x, real(db1), 'displayname', 'handel');
hold on
plot(x, real(db2), 'displayname', 'laughter');
hold off
xticks(-bnd:1000:bnd);
xlabel('Hz'); ylabel('dB')
legend show

[Nega Ejjigu]

Appreciated very much! I tried it.

I created a folder that contains my two wav files for istance one file name s and other u. then copied in workspace above code and run but generates following code :

Error using load

Unable to read file 's'. No such file or directory.

Error in FFTplotSecondCode (line 1)

load s

/////// written code at workspace :

load s
sig1 = y;
load u
sig2 = y;
minlen = min(length(sig1), length(sig2));
sig1 = sig1(1:minlen);
sig2 = sig2(1:minlen);
sig1 = sig1 - mean(sig1);
sig2 = sig2 - mean(sig2);
ff1 = fftshift(fft(sig1));
ff2 = fftshift(fft(sig2));
db1 = mag2db(ff1);
db2 = mag2db(ff2);
x = linspace(-Fs/2, Fs/2, length(db1));
bnd = 1000*floor(Fs/2000);
plot(x, real(db1), 'displayname', 's');
hold on
plot(x, real(db2), 'displayname', 'u');
hold off

[Walter Roberson]

[sig1, Fs] = audioread('s.wav');
[sig2, Fs2] = audiread('u.wav');

assert(Fs == Fs2);                                %sample rate must be same
assert(size(sig1,2) == 1 && size(sig2,2) == 1);   %single channel only supported

minlen = min(length(sig1), length(sig2));
sig1 = sig1(1:minlen);
sig2 = sig2(1:minlen);
sig1 = sig1 - mean(sig1);
sig2 = sig2 - mean(sig2);
ff1 = fftshift(fft(sig1));
ff2 = fftshift(fft(sig2));
db1 = mag2db(ff1);
db2 = mag2db(ff2);
x = linspace(-Fs/2, Fs/2, length(db1));
bnd = 1000*floor(Fs/2000);
plot(x, real(db1), 'displayname', 's');
hold on
plot(x, real(db2), 'displayname', 'u');
hold off
xticks(-bnd:1000:bnd);
xlabel('Hz'); ylabel('dB')
legend show

[Nega Ejjigu]

Dear Walter Roberson,

really appreciated for your hand. Being totally new to a matlab am keep asking each basic thing.

I got the follwing error :

Unrecognized function or variable 'audiread'.

Error in secondcode (line 2)

[sig2, Fs2] = audiread('u.wav');

% I still kept in one file folder file names named s and u then in same folder run .m file

Wondering still if I could get assistance

Kindly requested

[Walter Roberson]

[sig1, Fs] = audioread('s.wav');
[sig2, Fs2] = audioread('u.wav');

assert(Fs == Fs2);                                %sample rate must be same
assert(size(sig1,2) == 1 && size(sig2,2) == 1);   %single channel only supported

minlen = min(length(sig1), length(sig2));
sig1 = sig1(1:minlen);
sig2 = sig2(1:minlen);
sig1 = sig1 - mean(sig1);
sig2 = sig2 - mean(sig2);
ff1 = fftshift(fft(sig1));
ff2 = fftshift(fft(sig2));
db1 = mag2db(ff1);
db2 = mag2db(ff2);
x = linspace(-Fs/2, Fs/2, length(db1));
bnd = 1000*floor(Fs/2000);
plot(x, real(db1), 'displayname', 's');
hold on
plot(x, real(db2), 'displayname', 'u');
hold off
xticks(-bnd:1000:bnd);
xlabel('Hz'); ylabel('dB')
legend show

[Nega Ejjigu]

Thanks!I reallized that typo error (o missed).

now I got the below error :

Error using secondcode (line 4)

Assertion failed.