Crossfade between two sounds in realtime?

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Crossfade between two sounds in realtime?

(8 posts) (2 voices)

Started 1 year ago by machineboy
Latest reply from machineboy

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machineboy
Member

Hi, I've just started looking into iphone development. Coming from as3 I feel there is a lot to learn, but I've been watching Cocos2D with interest the past year and I really like it so far.

My first real coding attempt is to create a music instrument app, and I've been playing with the SimpleAudioEngine with good results. I really like its clean, friendly approach.

I've managed to make the app play a sample with gain and pitch variation depending on touch event locations. The next step I would like to accomplish is playing two samples simultaneously, with a crossfade between the two sounds based on accelerometer input (ie when the device is held upright it will play sound1 with gain 1 and sound2 with gain 0, and as you tilt the device the gain values will change in realtime).

Is this feasible, or am I looking at a lot of work here?

As I understand, SimpleAudioEngine does not support gain change when the sound is playing. Does anyone have any examples of how to control gain in realtime? I had a peek at the "Aphex" version of CocosDenshion and saw from the example that it supports actions to control fades, but is this what I want?

Thanks for any replies and hints. As a newbie, concrete examples are very welcome! :)

Posted 1 year ago #
Steve Oldmeadow
Administrator

Use the Aphex version of CocosDenshion but I'd recommend using CDSoundSource objects for your instrument's voices.

The FadeToGrey demo shows how to create and use CDSoundSource objects. If you have any questions just ask in this thread.

Posted 1 year ago #
machineboy
Member

Thanks for your reply, I've been looking at the CocosDenshion demo and the FadeToGrey app to try to figure out more. I must say it's a bit overwhelming for a newcomer to sort out what is happening, but that's just the game isn't it :)

Are you planning releasing more demos and examples for CocosDenshion? I really liked the short examples in the CocosDenshion cookbook as well. Short, simple examples are great for beginners like me.

Posted 1 year ago #

Steve Oldmeadow
Administrator

Maybe you don't know where to look. What is hard to understand about the following (taken from FadeToGrey)?

//Get sound sources for our files, we must retain them if we want to use them
//outside this method.
sound1 = [[sae soundSourceForFile:@"dp3.caf"] retain];

sound1.looping = YES;
sound1.gain = 1.0f;
sound1.play;

Posted 1 year ago #

machineboy
Member

Thanks, I had some problems accessing the sound1 object in my own function yesterday night, I will try to create a small demo from scratch based on the FadeToGrey code. I guess my problems lie with the new syntax and declaring and retaining objects. Probably should do some more simple, general tutorials and reading as well. Great work on the sound engine by the way, I'm really looking forward to harnessing its powers.

Posted 1 year ago #
machineboy
Member
Whee! After some initial trouble with setting up a new, clean project with the Aphex version, I was able to alter sound gain and pitch through the accelerometer. It works pretty well! I really like this sound engine and cocos2D in general.

I'm wondering about one thing:
```
- (void)accelerometer:(UIAccelerometer *)accelerometer didAccelerate:(UIAcceleration *)acceleration { 

//just an example
sound1.pitch = acceleration.x;}
```
It seemed a bit laggy and jumpy when doing it like this. Maybe set up some sort of tweening between values based on acceleration? I was testing on my iPhone 3G by the way.
Posted 1 year ago #
Steve Oldmeadow
Administrator

You should read Apple's documentation on the accelerometer. Basically you need a filter to smooth things out, tweening (or interpolation) between values is not sufficient.

Posted 1 year ago #

machineboy
Member

Thanks, I read about the high- and lowpass filters and it looks like a necessity if you want smooth input. I was messing with my own (very poorly written) smoothing function yesterday night and it seemed to work all right. It would probably still be too jumpy to get great interpolation between large values, but for smoothing gain it would probably work ok:

//Two schedules, one to get the accelerometer value every 0.1 seconds, one to linearly tween between old and new value every 0.02 seconds (5 step smoothing)
[self schedule:@selector(pollPosition:) interval:0.1];
[self schedule:@selector(tweenPosition:) interval:0.02];

-(void)pollPosition:(ccTime)dt{
	accyNew = acc;
}

-(void)tweenPosition:(ccTime)dt{
	counter --;
	if (accyOld<=accyNew){
		accyDifference = accyNew-accyOld;
		sound1.pitch += accyDifference/5;
	}else {
		accyDifference = accyOld-accyNew;
		sound1.pitch -= accyDifference/5;
	}
	if (counter == 0){
		counter = 6;
		accyOld = acc;
	}
}

There are probably hundreds of ways to do this better, but it's fun to see what can be done with intervals, sound and pitch :)

Posted 1 year ago #

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