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CCRMA Classroom

The CCRMA Classroom (Knoll 217) is our main teaching space.

2006 photo of CCRMA Classroom by Ge Wang

In the front (not shown in the photo) is a projection screen, white board, and presenters’ desk.

The audience/students sit in rows of desks with convenient power outlets.

There is a 6-channel surround sound system of Mackie HR824 speakers. Only the Linux Machine can access all 6; the many switchable audio sources connect to only the front stereo pair (above the projection screen).

A/V Switching

A custom Extron-based A/V switching system can very flexibly choose any of several video sources to display on the projector, and independently choose any of several stereo audio sources to come through the two main frontal speakers. Connectors on the front and back of the Extron system let you plug in a wide variety of sources such as phones and laptops. A Blu-Ray player and the Classroom Linux Machine are permanently connected and always available as audio and/or video sources.

Commonly needed cables hang coiled from hooks on the side and commonly needed adapters live in the glass cookie jar on the desk.

Linux Machine

A CCRMA Linux Workstation cmn8.stanford.edu is accessible from the presenters’ desk.

It has a MOTU 1248 connecting it to the full sound system, located in the rack with the Extron system, below the document camera. A 4-channel XLR snake (normally coiled and stored on the side of the rack) makes it easy to plug into the 1248’s microphone inputs.

Beware that Linux doesn’t always successfully talk to the MOTU the first time you try so you might need to “play” or “start audio” a few times.

Also beware that by default Fedora will often perform an automatic 7.1 surround mix that you probably don’t want. That’s why the largest-font sticker on our surround gain controller says

Turn down all faders when 
not using surround sound

The best way for Linux software to access multiple audio channels is JACK, avoiding these and other problems. (JACK may not start the first time, but after it does start, all other software going through JACK can connect reliably to the MOTU.)

Two Different Video Monitors for Linux

Jonathan Abel gets migraine headaches from certain video monitors. To avoid this he has identified an old low-resolution (XXX how low?) ViewSonic LCD monitor that works for him.

Matt found a sufficiently passive KVM switch that can be run “backwards” (with one video source (namely the Linux output) feeding either of two monitors instead of the usual one monitor being fed by either of two video sources).

If you want to use the Classroom Linux machine and are not Jonathan Abel we recommend you select Normal Monitor.

Any time you log in or out of the Linux machine it re-scans the monitor and will detect the current display and set its video resolution appropriately. So even if the login screen looks weirdly low-res, just log in anyway and it should correct itself.

Most people should press the Normal monitor button. (Actually most of the time it should already be in this state.)
The Classroom Linux machine using the “Normal” monitor (mounted on a swivel arm)
Only Jonathan Abel should press this button
Only Jonathan Abel prefers this low-res monitor

(Surround) Sound System

During summer 2018 we temporarily upgraded the CCRMA Classroom’s sound system from 4 to 6 audio channels. We aspire to 8 or more along with additional acoustic dampening (to control the excessive reverb).

Only the Classroom Linux machine can access the surround speakers, via a MOTU 1248 in the rack with the Extron system, below the document camera.

(Maybe someday a KVM switch will mediate laptop access to this MOTU (as in Studio D), but not yet - consider JackTrip as a way to get multichannel sound from another computer (your laptop) to the 6 speakers via cmn8.)

As in every other CCRMA multichannel space, the channels are numbered in stereo pairs from the front to back of the room. So with 6 channels that gives:

  1. front left
  2. front right
  3. mid left
  4. mid right
  5. rear left
  6. rear right

(Note that “left” and “right” are from student/audience perspective (as you look at the projection screen), which is the opposite of the instructor perspective (as you sit at the desk looking out at the students).)

The front stereo pair is fed from the Extron switching system, so that those two speakers can flexibly play stereo from multiple sources, with gain control and audio mute functions on the little touchscreen. Therefore to use surround you must select “Linux” on the Extron system (under “Audio”) - otherwise a different audio source (likely silence) will come out of the front speakers.

The gain control for the four surround speakers is controlled by a vintage bespoke 4-fader gain control box (built ages ago by Jay). The faders all have labels like “Linux #5 / rear left”. (The gain for the front two (as a linked stereo pair) is via the Extron touchpanel.) There’s no calibrated way to keep all 6 channels’ relative volumes the same; it’s on you to set the levels to balance the 6 channels properly.

Audio Inputs

The four microphone inputs to the MOTU 1248 (on the back of the box) are connected to a labeled 4-channel XLR snake so you can easily plug in up to 4 microphones. The snake is normally stored coiled up on the side of the Extron rack, alongside the spare cables.


This page of CCRMA documentation updated Wed May 20 08:48:18 PDT 2020 by matt.