An Audio Issue

One thing that I (and many others judging by forum posts) have run into is the fact that the Blackberry isn’t very good at mixing more than one sound together. You’ll be listening to music, or playing a game with music, and suddenly you’ll get a text message, and it will simply terminate the current sound and play the new one. If you’ve got a friendly application, it will restart/resume the original audio, but it’s a jarring audio experience.

What I’m about to post won’t fix that. However – developers also run into the issue when they want to mix sounds together in their applications and games. Play 2 or more sound effects simultaneously and/or while music is playing. I’ve seen official RIM developers comment that certain devices can achieve two simultaneous sounds by instantiating the Player class twice – but from what I gather, this is on GSM only phones – and still limited to two. On CDMA devices, you’re completely out of luck.

The Cheap and Quick Workaround

In my 6 part tutorial on writing a Blackberry game, in the audio article, I mentioned how the Alert.startAudio method can be used for simple sound effects (tone/duration pairs) that will play simultaneously while your midi or mp3 music plays in the background. For many applications, this is enough if you don’t need sophisticated sound effects.

The Start of a Mixer

I’m guessing that the limitation is imposed by the audio chipset/DAC inside of CDMA devices, and perhaps RIM realizes the CPU time involved in a software based audio mixer would slow the phone down too much. However, I think the software option should be there, and developers can use it if they’d like – they might not need a large amount of CPU, or might be dealing with low quality sound files – there are a few scenarios where a software mixer would just be a nice options.

Tonight I sat down and wrote a quick and dirty proof of concept application showing a PCM audio mixer in action. I loaded in 3 audio 44.1khz 8bit mono files and mixed them together in real time. I didn’t normalize the audio at all, so its a little soft, but the code works, and could be expanded on quite a bit to make a full featured mixer. Maybe I’ll run into problems down the road that RIM already has, but it’ll be interesting nonetheless.

Here is the video of the test: