Duration of generated sound not correct

Hello,

I need to create 25ms ramped sounds with different frequencies. I was successful in creating the ramp, but something is not right with the duration as it is always longer than what is inserted. I think it is related to the sampling rate but I cant figure out the exact problem:

Amp = 0.5;          %amplitude
Freq = 1000;        %Frequency of the sound
Fsam = 44100;       %Sampling rate
Dur = 2;            %Duration of the sound in seconds


dt = 1/Fsam

Time = 0: dt :Dur-dt;

y = Amp*sin(2*pi*Freq*Time);
  
plot (y);
xlabel('Time (ms)');
ylabel('Amplitude');
 
%% Ramp the sound
y = Amp*sin(2*pi*Freq*Time);
RampDur = 0.01;
NsamRamp = round(RampDur/dt);
OnRamp = linspace(0,1,NsamRamp);
OffRamp = fliplr(OnRamp);
y(1:NsamRamp) = OnRamp.*y(1:NsamRamp);
y(end-NsamRamp+1:end) = OffRamp.*y(end-NsamRamp+1:end);
plot(Time, y);
xlim ([0 Dur]);
 
 
sound(y)
 

Thanks for your support!

Answer 1

[Scott MacKenzie]

Change

sound(y);

to

sound(y,Fsam);

The sound function assumes a sampling rate of 8192 Hz. If a different sampling rate is used, it must be provided as a 2nd argument.

[Anton M]

Thank you Scott this works! And it also fixed the frequency which was my second question as the 1kHz sound did not sound like a 1kHz. Awesome!

[Scott MacKenzie]

@Anton M, you're welcome. Good luck.

Answer 2

[Mathieu NOE]

hello

some minor modifications and suggestion

Amp = 0.5;          %amplitude
Freq = 1000;        %Frequency of the sound
Fsam = 44100;       %Sampling rate
Dur = 2;            %Duration of the sound in seconds
dt = 1/Fsam;
% Time = 0: dt :Dur-dt; % no 
Time = 0: dt :Dur;  % yes 
y = Amp*sin(2*pi*Freq*Time);

plot (y);
%xlabel('Time (ms)'); % no 
xlabel('Time (s)');  % yes
ylabel('Amplitude');

%% Ramp the sound
y = Amp*sin(2*pi*Freq*Time);
RampDur = 0.01; % 25 ms ??
NsamRamp = round(RampDur/dt);
window = ones(size(y)); % init window to 1
window(1:NsamRamp) = linspace(0,1,NsamRamp); % ramp up section 
window(end-NsamRamp+1:end) = linspace(1,0,NsamRamp); % ramp down section 
y = window.*y;
plot(Time, y);
% xlim ([0 Dur]); % not needed

still I don't understand where the 25ms should apply (the ramp duration ? so why define RampDur = 0.01 ? )

the code does generated a 2 seconds long signal as you requested - there is no big surprise here ; what is your issue ?