How is this circuit giving 5v to Teensy?

I'm hoping to make the below circuit:

what I don't understand is how the SID chip is getting 9v to VDD from the battery, but the Teensy 2.0 is getting 5v (I assume!)

I would ideally like to supply 9v DC from a power adapter.... are the two capacitors either side of the power supply stepping the voltage down here? For some reason I had the idea a bit more than that was required to reduce the voltage...

I'm guessing that the expectation is that the Teensy is powered via the USB socket.
The SID chip requires 2 power sources, 9 volt from the battery and 5 volt which it gets from the Teensy.

If you want to eliminate the 9 volt battery, you can get a cheap boost converter 5v to 9v.

great, thanks - I thought that might be the case, but the schematic seems to exclude the 5v supply (as you say, possibly because it's assuming usb)

There's no difference to stepping down from the 9v supply to stepping up to 5v right?

Stepping down is even easier. I'm not sure of the Teensy 2.0 has a built in regulator (it is greyed out on the schematic I found) so maybe you'd have to do that externally. If you used a Arduino micro pro instead (it has the same Atmega32U4 chip) which has also a built in regulator, you might be able to feed 9 volts to that so you'd have both 5 volts and 9 volts available with only one power supply. But check the specifications of all devices (power requirements etc.) to see if that is a viable option.