Old Ideas Return

When breaking up a piece of music into various layers that play independently a major concern is how to keep these layers in time with each other. Wwise achieves this by making sure that each layer is of the same sample length. This is also how I got round the issue during Dare To Be Digital. The whole point of this project, however, is to allow for layers to be of varying lengths. So how can the synchronisation of these layers be achieved?

The first method I looked into simply involved counting the beats. If you have a sequence that you know the tempo and time signature you can use that to work out how long, in milliseconds, a single beat should be. A timer can then be used to count the milliseconds between beats.

While in theory this is a "sound" idea (sorry, but I had to get that pun in eventually) issues can occur with synchronising the start of the timer with the start of the sequence. A separate thread created by the FMOD api handles playback of the sounds meaning that the timer is being calculated outwith the sound playback. With the time-critical nature of audio, and particularly music, this method is inevitably too unpredictable to confidently use, as the timer will always be separate from the source.

After realising the pitfalls of using a timer I then returned to my original idea of using an audio sample as a "click track". The click track was based on a sample containing a single bar of audio that had markers placed on the beats. During playback of this sample when the playhead passed one of the markers a callback would be triggered indicating that we've hit a beat. With this method the timing is kept in the same thread as the playback of the audio, so timing discrepancies are reduced.

This method was used in the Dare To Be Digital game, Origamee, to synchronise the audio cues with the beats of the music. However, it didn't work properly as it suffered from the delay of looping static sounds, so the cues would go out of time. Luckily as the tempo for the game music was fast it was hard to spot the timing issues with the cues, and because the music layers were the same length the music itself wouldn't go out of time. Now that I can implement sample accurate stitching this can be used to resurrect the click track, as it overcomes the issue with the loop delay.