Something that was also very important to us was expanding the accessibility of the series. This was something else that heavily impacted on our audio system. We knew that Guitar Hero was a partyfavorite. We also knew what it was like to miss the start of a song and having to wait around, or having to let other players down by deserting a song part way through as we're dragged away by other friends or burning party food.
With Guitar Hero 5, we created a new mode called "Party-Play." This mode allows players to join in and drop out of the game at will, while a song is in progress, and even while other players are playing.
This feature demanded a dynamic system that can reconfigure itself smoothly while playing back audio. For each of the nine stereo tracks of the song, we create a DSP Route for each instrument. DSP effect chains on each route are definable by our designers, and CPU willing, they could put whatever they wanted on these routes.
There is also a stand-alone Reverb processor, which we use as a "Send Effect." Each route can "send" audio to this effect at a definable volume and pan setting. This all allows us to add, remove and "move" instruments on-the-fly.
Even without a drop-in, drop-out system, the sheer number of player and instrument combinations means that we have to do a lot of reconfiguration every time a new song is selected. The instruments that influence the song streams are guitar, bass or drums and for guitar and bass, we must add a new DSP effect, the whammy.
What's more, more than one player can choose to play the same instrument. In the case of guitar or bass, we need to add a second whammy effect and we must split the track into two separate DSP Routes, both with separate whammy effects. However, since the buss (or final mix) volume is applied later on in the processing, we must recombine these tracks later on.
Although latency isn't strictly an audio problem, it is a big concern in a game like Guitar Hero, and many things must be done to address it which do touch on these systems. To make the game playable, we must synchronize the controller input and scoring with the video and audio. There are many variables involved with each system, and that is why we need the calibration screen.
You would be surprised how much latency modern TV sets can introduce in both the audio and video. Many televisions have a special mode called "game mode" to deal with exactly this issue.
Typically, this mode will turn off special video smoothing algorithms designed to "upscale" or otherwise make the picture look better, but require the television to store and delay several milliseconds of video and sometimes audio. The TV is also not the only thing to blame. Each game console has its own audio, video and wireless controller latency figures as well.
There are two parts to the calibration screen, one for synchronizing the video, and another for audio. The user is prompted to rhythmically tap the controller in time with scrolling notes on the screen, and then later with audio beeps. The video portion actually calculates the round-trip lag time from video output to controller input latency time, and adjusts the offset of the note highway so that the notes match up with the controller input.
The audio test tests the lag time for the audio output. Based on the calculated lag time, the song audio will be delayed so that it matches up with the controller input.
Game audio doesn't always get the credit it deserves and I think that's because it tends to be the most powerful when it is at its most subtle. A game like Guitar Hero is fun to make because it lets us focus more on the sounds. It's all about music, atmosphere, performance and cheering crowds.
The technology we used had to help us capture all of that and give our sounds a descriptive quality that most games shift on to their graphics. If you do well, the sound will tell you, if you don't do so well you will hear that also; when you use a power-up everyone will hear it in your notes, where you are standing in the line-up is reflected in the audio, as is the hall where the game is set.
As you can appreciate all of this takes a lot of subtle (and not so subtle) things happening in concert, and while we did a lot of things to try make Guitar Hero a success I think that the elements I've outlined above give a pretty good look at some of the behind-the-scenes audio that might go unnoticed but doesn't go unfelt.