# Duration of generated sound not correct

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Anton M on 25 Mar 2022
Answered: Mathieu NOE on 25 Mar 2022
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)

Scott MacKenzie on 25 Mar 2022
Edited: Scott MacKenzie on 25 Mar 2022
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.
##### 2 CommentsShowHide 1 older comment
Scott MacKenzie on 25 Mar 2022
@Anton M, you're welcome. Good luck.

Mathieu NOE on 25 Mar 2022
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 ?