How do I decrease sound exponentially when a user press button stop on my player app ?

6 次查看（过去 30 天）
Bastien Lechat
Bastien Lechat 2017-10-4
评论： Walter Roberson 2017-10-4
% code
afr = dsp.AudioFileReader('track1.wav');
adw = audioDeviceWriter('SampleRate', afr.SampleRate)
app.dec =1;
while ~isDone(afr)
audioIn = afr();
audioout = audioIn * app.dec;
adw(audioout);
end
with for the stopbutton
% code
t = 0:1/441000:4;
alpha = 0.1;
app.dec = exp(- alpha *t);
Basically I just want to avoid the brutal stop (which give me bad harmonics) by decreasing the sound smoothly with an exponential when we press the button stop.
Thank you !
  1 个评论
Jan
Jan 2017-10-4
Do you want to load a WAV file, fade out the sound in the last 4 seconds and save the file? Did you draw the curve?
t = 0:1/441000:4;
alpha = 0.1;
dec = exp(- alpha *t);
plot(t, dec)
Are you sure that this is the wanted amplification?

请先登录，再进行评论。

请先登录，再回答此问题。

采纳的回答

Walter Roberson
Walter Roberson 2017-10-4
Make counter and alpha shared variables. Initialize counter to 0 and alpha to 0. Enter your loop. In it,
t = counter + 1 : counter + length(audioin)
audioout = audioin .* exp(- alpha * t/44100);
counter = t(end);
And in the stop button callback, set the shared variables
counter = 0;
alpha = 0.1;
That is, the exp is done every time, but with alpha zero it has the effect of multiplying by 1. When the stop button is pressed then a nonzero alpha is put into effect leading to exponential drop off in volume.
Just make sure that you add something to tell it to stop looping when counter reaches or exceeds 4*44100 after the stop is pushed
  2 个评论
Bastien Lechat
Bastien Lechat 2017-10-4
编辑：Bastien Lechat 2017-10-4
When I'm doing an error occur telling me :
Error using audioDeviceWriter/setup
"The number of input channels must be less than or equal to 255."
Do you know where it comes from ? Edit: I just had problem with matrix dimension
But I still have a problem where it's telling me:
Error using audioDeviceWriter/setup: A given audio device may only be opened once.
Walter Roberson
Walter Roberson 2017-10-4
function go_button_Callback(hObject, event, handles)
afr = dsp.AudioFileReader('track1.wav');
adw = audioDeviceWriter('SampleRate', afr.SampleRate)
app.dec =1;
stopping = false; %shared variable
counter = 0; %shared variable
alpha = 0.; %shared variable
set(handles.stop_button, 'Callback', @(hObject, event) stop_play_nested(hObject, event, handles), 'enable', 'on' );
while ~isDone(afr)
drawnow(); %give a chance for graphics interrupt
audioIn = afr();
t = (counter + 1 : counter + size(audioIn, 1)).';
audioout = audioin .* repmat( exp(- alpha * t/44100), 1, size(audioIn,2) );
adw(audioout);
counter = t(end);
if stopping && counter >= 44100 * 4; break; end
end
set(handles.stop_button, 'enable', 'disable');
delete(afr);
delete(adw);
function stop_play_nested(hObject, event, handles)
stopping = true; %shared variable
counter = 0; %shared variable
alpha = 0.1; %shared variable
end %end of stop_play_nested
end %end of go_button_Callback

请先登录，再进行评论。

更多回答（0 个）

类别

在 Help Center 和 File Exchange 中查找有关 Audio Processing Algorithm Design 的更多信息

标签

Community Treasure Hunt

Find the treasures in MATLAB Central and discover how the community can help you!

Start Hunting!

Translated by