Any way to speed up music during run-time?

EDIT: Better description in the newest post.

Like Sonic's Speed Shoes, which make the music faster while active, but the music continues from the same point, it doesn't start over.

I had a solution for a similar problem where a new instrument overlays the current track, by having both songs (with instrument and without) play at once, and you mute one to switch them. That ensures they'll play at the same point in the song when switching, but since speeding up the song, y'know, changes its speed, that solution can't work.

Is this even possible?

You can play a song on a certain channel, then change the channel's frequency ratio to speed it up.

Well that was sitting right in front of my face...

Sounds like that raises the pitch, though. I guess I'll have to make a second track that has a lower pitch, then switch to that and change the ratio... A bit of work, yeah, but it'll have to do if there isn't any other way. Thanks.

I hate to bump a semi-old topic, but apparently that solution isn't quite good enough. I can't think of a good way to describe it without, well, completely describing it, but I guess I have to in order to find a proper solution.

What I want to do is replicate what happens with Sonic's Speed Shoes. When you pick them up, the music gets faster without changing pitch, and when time runs out, the music reverts to its normal speed. My previous method covers everything EXCEPT when times runs out -- if you switch back to the normal track, it won't be matched together since the other one was sped up.

Basically, the ideal solution would speed up a single track, without changing pitch whatsoever. If there's a method of changing pitch, that'll work too, since I can change the frequency ratio (which makes it higher pitched) and then correct the pitch separately afterward. If I can't, I'll have to settle for the method most Sonic fan-games stick with: use a completely different song for Speed Shoes.

Is there any way to do any of this?

Have 2 pieces of music pre-recorded, one twice the tempo of the other, and start them both playing together at the same time, with the volume of the faster one set at zero and it's frequency set to half the normal.

Then when you need the speed-up music to kick in, simply set the fast music to it's normal frequency, and it's volume to normal, and the normal music volume to zero and it's frequency to double it's normal.

This should always keep them in sync as you switch between the two.

Krush.

That's... diabolically brilliant.