Syncronize metronomes

Programming Questions

mikailis

in Programming Questions • 3 years ago

Hi

I am trying to build a simple metronome. My code is

void keyPressed()
{
if (key == 'c')
{
   metro1 = minim.loadFile("1st metron.mp3",buffersize);

   metro1.loop(tempo);

}else if(key == 'v')
{
metro1.close();

}

}

tempo is an integer
i also have a virtual metronome which is shown on the screen

///////////////////////////////////////METRONOME////////////////////////////////////////

if(millis()-start >= tempo)
{
start = millis();

counter++;

xpos = xpos+width/17;
if(xpos>=width)
{
xpos=2*width/17;
}
if(counter==5)
{
counter=1;
}

My problem is that after some seconds it appears a delay between the two countings.

Why is this happening and how can i deal with it?

Thank you.

Replies(3)

noncom

The only thing that comes to my mind is that you get inaccurate with your milis()-start thing.. try putting println(millis()-start); into the metronome to track it's iterations.. if numbers differ then this is the reason. Calculation inaccuracy in loops may build itself higher with time..

You see, it takes, say 100 milliseconds to run through your metronome if (xpos>=width) is false and it takes, say +10 (all in all 110) seconds to run through the metronome if it runs inside the if. Remember, when working with timing, that each command takes time to perform. you may measure timing like this:

for (int i = 0; i<100;i++)

{

mili1 = millis();

println("\n\nWe enter the cycle on " + mili1 + " milliseconds");

if (a>5) a = 0;

a++

mili2 = millis();

println("We exit the cycle on " + mili2 + " milliseconds");

println("It took us " + (mili2 - mili1) + "milliseconds to run the cycle);

}

mikailis

Re: Syncronize metronomes

3 years ago

Thank you noncom. Your reply was very enlightening.

Running your simple sketch above it gave me differences of 1-2 milliseconds. is this general for the enviroment?

i can imagine that when you have multiple conditions, delays are getting bigger and causing the latency i am dealing with.

for example, i have created a simple pulse sequence(mp3 file) of notes with 500 ms interval for each note. loading the metronome
like

metro1 = minim.loadFile("1st metron.mp3",buffersize);

metro1.loop(500);

and loopinf it is resulting in an annoyning delay after some pulses.

As far as i can see, my code is raw and quite long so maybe i have to run timings in a different way. Should i not use millis();

Thanks anyway,

noncom

Re: Syncronize metronomes

3 years ago

Yep, you see, 1-2 milliseconds inaccuracy results into at least 1 second inaccuracy after 1000 cycles. And if your sketch runs the cycle, say, 30 times a second, you will get the annoying rythm offset in 33,3(3) seconds. And it's just a imple IF.

Actually, I have never worked with sound and I do not know, how to deal with this. But defenitely there are ways because tonns of perfectly synchronized music software exists. Maybe they deal with different threads (imagine a separate thread, which only counts for clicks and only send messages to your main thread, doing nothing else so no garbage there. and when there is no click - sending just an empty message taking the same amount of time as with click message. I don't know if it works, just an idea).

Also, you see, I do not know, how the Minim library handles all the stuff. You can probably address it's creators with questions. Possibly, if you find a way to make a perfect metronome, you could write your own loop() with play() in it to handle the looping by your design.

For now, I have googled for "programming a metronome" and came across this link: http://www.mediafire.com/?mnqgmznlyyw where you can download an example in Delphi. Try looking inside the *.pas file in the archive and possibly, adapt the algorythm to Processing.

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