I'm sorry if I'm posting this in the wrong section. I'm new to Sonar and I have my MPD32 hooked up USB. I followed the steps in the video on YouTube "Sonar X1 MIDI for Beginners" and every time I hit a pad the meter shoots up, so the pads are recognized, but there's still no sound output. I've tried a few different outputs, patches, etc. I don't know if either of these details make any difference, but I am hooked up via USB, and I'm using the demo version of Sonar Artist.

check your driver settings in preferences.
you need to specify the Akai as a device in midi preferences.
also make sure the output of the midi track is indeed feeding the synth you inserted.

Which synth are you trying to drive with it?
 
Make sure you have Input Echo enabled on the MIDI track

BobF
Which synth are you trying to drive with it?
 
Make sure you have Input Echo enabled on the MIDI track

ASIO4ALL v2 HD Audio capture 1 is the only input driver I see available.
 
I have the box "always echo current MIDI track" in playback settings checked if that's what you mean.

OK,  If the AKAI MPD32 is connected and the midi box is cheeked under Preferences > Midi >  Devices > Inputs,   do following
 
Go to  Insert > Softsynth > choose a softsynth, preferably a keyboard if possible.
You will now see the Option Dialogue Box
 
Select the following  3 items when the option dialogue box appears:
1. Simple instrument track.
2. Synth Property Page
3.  Synth View rack
OK
 

 
When the instrument track appears in Sonar and the instrument GUI appears, select a Keyboard tone that you want to hear for the piano.  Now click on the track number in which the keyboard is on and press the MPD32 buttons, you should now hear the keyboard.  
 
When working with Drums its the same thing basically.

If you don't see the Akia MPD32 midi driver, go to the website and get the latest Midi driver

Accumulus
I'm sorry if I'm posting this in the wrong section. I'm new to Sonar and I have my MPD32 hooked up USB. I followed the steps in the video on YouTube "Sonar X1 MIDI for Beginners" and every time I hit a pad the meter shoots up, so the pads are recognized, but there's still no sound output. I've tried a few different outputs, patches, etc. I don't know if either of these details make any difference, but I am hooked up via USB, and I'm using the demo version of Sonar Artist.

The MPD32 is a controller, not an audio device so it won't make any sound, only trigger a soft synth that generates sound.

I have one of these. (don't use it anymore) but I believe I did have to go to Preferences/Midi/Drivers
and select the check box.
https://www.cakewalk.com/Support/Knowledge-Base/2007013179/I-cannot-hear-MIDI-playback
 

You need the drivers for the MPD!