Multi-Channel Audio
Key Terms:
• Audio Interface
• Outputs
• Line-in Inputs
• Mixer Sub-Out Vs Mixer Main Out
• Mixer Output assignment
Relevant Notions in Logic:
• Preferences -> Audio -> Devices -> Output Device (for 618, choose "Universal Audio Thunderbolt")
• File -> Project Settings -> Audio -> Surround Format (for 618, choose Quadraphonic)
Notes
Multi-channel Audio
Multi-channel audio simply means having more than one audio stream (i.e., channel) at a time. So strictly speaking, stereo audio (which has two channels, and is what all CDs and MP3s are) is multi-channel audio. However, multi-channel audio generally refers to using MORE than two channels at a time. The important idea to remember is that each channel goes to its own speaker (so two channel = two speakers, four channels = four speakers, etc.).
Any number of channels is theoretically possible, but in practice is limited to the hardware at hand. Some standard formats exist: Quadraphonic (4 channels going to four speakers, setup in a square or rectangle formation), 5.1 (five channels going to five speakers, setup in a quasi pentagon), 7.1 (seven channels going to seven speakers, setup like 5.1 but with added rear speakers), etc.
In 618, we'll be using a Quadraphonic setup.
To make multi-channel audio possible, we need:
1) A computer with software capable of multi-channel output. For us, this is the iMac (or your laptop) and Logic Pro.
2) A multi-channel audio interface. For us this is the Universal Audio Apollo X8 Thunderbolt (the dark grey box with the silver and green knobs on the right of the iMac). An interface is a device that converts digital signals from the computer, and converts them to electrical signals to be used by mixer and speakers (see "DAC" from your "digitizing audio" class notes).
3) (Optional) A mixer with multiple outputs. We are not using a mixer in 618.
4) Speakers connected to the interface or mixer. For us, these are the two Genelecs in front of the desk, and the two other Genelecs sitting on the cabinets at the back of the room.
Procedure to Obtain Multi-Channel Outputs in 618
To send sounds to the rear speakers:
• Each track can be assigned a specific pair of outputs on the interface. To use the rear speakers in 618, select "Output 3-4" on one of your tracks:
• Play something from the track you just assigned to Output 3-4 and you should now hear something form the back speakers.
• Then by using the panning knot on that track, you can make the sound go from the Back-L speaker to the Back-R speaker.
This is the simplest way to send sounds to the rear speakers. If you want to have one sound go from the front speakers to the rear speakers, then you must duplicate that sound's track (by pressing the "Create New Track with Duplicate Settings" button)….
…..change the outputs of that new track to "Output 3-4", and edit the sound between the two tracks:
To Use the Surround Panner (Most Flexible Way to Send Sound to All Four Speakers):
1-Go to File->Project Settings->Audio, and select "Quadraphonic" in the Surround Format:
2-On one of your tracks, choose "Surround" as the output:
This will automatically change the panner to reflect the surround format:
3- Use automation to control the Angle; NOTE: 0deg is front center; 180deg if back center; positive angles are on the right; negative values are on the left (i.e., avoid using the diversity and spread options):
Two tips:
1) Avoid using the middle position with the surround panner. This simply spreads the sound evenly to all speakers and makes it louder, but not more spatial sounding, and listeners sitting close to a speaker won't hear the sound coming from the other speakers.
2) Avoid placing a sound statically between two speakers, for the same reasons as tip 1).
