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CCRMA Classroom

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

In the front (not shown in the photo) is a projection screen, white board, pair of loudspeakers (Mackie HR824), and presenters’ desk.

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

Projector

An LG GRU510N 4K laser projector is mounted to the ceiling.

Audiovisual Selection

Use the Kramer system to plug in and choose one video source.

Use the mixer to mix the audio (including stereo from the selected HDMI source).

Audio System

Actually it’s now an Allen & Heath CQ-12T; maybe you want to download their CQ MixPad app (under “Software Downloads”) at the manufacturer’s resources page.

XXX update all references to Mackie 1202; include new images showing the mixer and its UI…

The heart of the Classroom’s audio system is this Mackie 1202-VLZ3 mixer:

The Mackie’s Alt 3/4 output feeds Zoom; therefore pressing “mute” on a channel actually means “Zoom only”. To completely eliminate a sound source, turn the gain knob fully counterclockwise.

Audio Inputs

lav mic

Wireless lavalier microphone for presenter

room mic

PZM mic affixed to the ceiling of the room that does a decent job of carrying the sound of people in the room

analog

From the dangling stereo audio cable with a 1/8 inch (aka 3.5mm) TRS unbalanced analog stereo connector, meant to plug into the headphone jack of a laptop, phone, etc.).

HDMI

Stereo audio decoded from the Kramer’s one selected video source.

Linux

Stereo sound, in analog, from the Linux machine’s connected MOTU 1248 audio interface

Zoom (Mac mini)

sound from the Mac mini dedicated to running Zoom, straight from its headphone jack in 1/8” stereo unbalanced analog.

Audio Outputs

We use almost all (!) of the Mackie’s audio outputs (not including inserts), namely (in stereo pairs):

“MAIN” (XLR on back)

Classroom overhead stereo loudspeakers; controlled by “overall” / MAIN MIX knob.

“MAIN OUT” (1/4” on top)

[not currently used]

“AUX SEND 1/2” (1/4” on top)

To Mic 2 of the “Drum Machine”; “left” channel (aka #1) unfortunately controlled by “SEND” knob of “AUX 1 MASTER”, which should be left at “U” (for “unity gain”)

“CONTROL ROOM” (1/4” on back)

To the Ballroom Adam stereo speakers, via an “Alto Professional Stealth Pro 2-Channel Wireless Audio System for Active Loudspeakers” (manufacturer’s page) (so that no speaker cables will be in the way of shutting the door between Classroom and Ballroom); controlled by both “overall” / MAIN MIX and “ballroom” / CTL ROOM/SUBMIX.

“ALT OUTPUT” aka “L/3” and “R/4” (1/4” on back)

To Mic 1 of the “Drum Machine”; controlled by “overall” / MAIN MIX, consisting only of the channels for which the MUTE aka ALT 3-4 button is pressed. This is specifically so we can send the overhead room mic to Zoom without amplifying it in the Classroom, but it works for lav mics (to make a perfectly-audible-in-person presenter more clear over Zoom) or any other “muted” sound sources intended for streaming, recording, live processing, etc.

Expanded A/V System

What’s going on with all this gadgetry?!?

• Presenter’s A/V sources go into the Kramer and audio mixer.

  • Kramer’s selectable HDMI 3 input is now coming from the Zoom Mac Mini , e.g., so when a person asks a question over Zoom you can put their face on the big projection screen. (Also good for video feedback effects.)

• Audio from mics, an analog input cable, the Kramer (selected HDMI), and the Zoom Mac mini (so you can hear when people ask questions over Zoom) go into the audio system: a Mackie 1202 mixer. The mix drives three sound systems:

  1. Stereo in the Classroom
  2. Mirrored stereo in the Ballroom, if connected (separate gain control)
  3. Your “microphone” in Zoom (via the “Drum Machine”)

• The video output of the Kramer is split to produce three identical mirrored copies sent to:

  1. Projector in the Classroom (via the Kramer’s built-in HDBT (video-over-Ethernet-cable) output)
  2. Large flat-screen TV in the Ballroom (via output 1 of an OREI 18G HDMI splitter, to an HDMI-over-Ethernet extender transmitter, to an ethernet jack in the floor of the Classroom under the presenters’ desk, via the sysadmins’ building-wide Ethernet patching, up through another jack in the floor of the Ballroom, via one last Ethernet cable through a conduit you can walk over, to the HDMI-over-Ethernet extender receiver, and via HDMI to the TV).
  3. The Kramer input to the video production system (via output 2 of that HDMI splitter, to the “OUTPUT” HDMI jack on the back of the cart, via an HDMI cable into input 1 of the “Drum Machine”)

• The video production system essentially consists of the cameras and video switcher (“Drum Machine”)

Cameras

We now have three AVER TR313 V2 pan/tilt/zoom auto-tracking cameras (manufacturer’s product page) to cover the Classroom:

1. The Desk camera is mounted on the desk to get a close-up of the presenter’s face.

2. The Front camera is located at the front of the room (between the projection screen and the door to the closet), pointed at the faces of the audience.

3. The Rear camera is located at the rear of the room (underneath the rear left loudspeaker), pointed at the presenter, projection screen, and the backs of the heads of the audience.

Each is selectable from the video switcher as an image source.

Each is controllable from a handheld remote control. The top row of buttons selects which of the three cameras the remote is “talking to”, which is almost always #1 because Front and Rear default to useful wide-angle shots but Desk works best when tracking the presenter.

You can manually position the image with the four directional arrow buttons (up, down, left, right) and manually zoom by pressing + (zoom in) or - (zoom out) on either the ZOOM SLOW or ZOOM FAST buttons of the remote control.

The auto tracking feature will “latch onto” a person (such as the presenter) and smoothly pan/tilt/zoom the camera to keep that person in the frame, e.g., as they move between the whiteboards and the desk:

• Turn it on with the button labeled ON just under the words AUTO TRACKING.
• Turn it off by manually positioning the camera.
• The button labeled SWITCH (just under the ON button) will make the camera attempt to follow the other person in the frame, but it can get confused.
• The safest way to make it track another person (e.g., the next speaker) is manually pointing the camera at the new person (thereby turning off tracking) and then hit the ON button (thereby turning it back on, hopefully now tracking the new person).

Typically the lighting on the presenter’s face is horrible, because you turn down the room lighting to be able to see the projector, so there’s almost no light on their face but tons of backlighting from the projection screen behind them. Two camera settings make this much better; each has a button on the remote control to toggle: WDR and BLC.

Video Switcher

The Blackmagic ATEM video switcher (“Drum Machine”) is the heart of the video production system. It has vast capabilities; we use it primarily to select which (combination of) camera view(s) will be recorded and/or sent to Zoom. From Zoom’s point of view, this device is the connected webcam (and microphone); whatever the ATEM is outputting (e.g., your laptop video via the Kramer, with your face superimposed in a small picture-in-picture rectangle) is “your camera” as far as Zoom (or any software on the Mac mini) is concerned.

Model

Blackmagic ATEM Mini Extreme ISO

Nickname

The “Drum Machine” (because of the light-up touch pads)

Output

It acts a “webcam” and stereo USB “microphone” to the (mainly dedicated to Zoom) Mac mini

Inputs

Cameras and the split output of the Kramer. Each has a corresponding labeled and numbered big touch pad for selecting it.

Display

Has its own adjacent small video display monitor.

Best button

Try pressing the M.V button for “multi-view” mode to see all inputs (including audio metering) on the display.

Mac Mini

There’s nothing too special about this Mac; it’s just for running Zoom (etc.).

Its video input “webcam” (with stereo digital audio) is the “Drum Machine” (so you can video produce your class/lecture/concert/etc. for streaming and/or recording).

Its video output is split (mirrored) to a “Janus-headed” pair of identical video monitors, as well as going to the HDMI 3 input of the Kramer (so you can show Zoom on the projector).

The audio output goes to the audio mixer (so you can hear Zoom in the loudspeakers).

It doesn’t connect to CCRMA accounts, but you can easily just log in as “A Zoom User” (with certain restrictions, such as all files being deleted when you log out). (Otherwise you need a local account (meaning just for this one computer): ask staff to log in (as admin) and perform Apple’s usual way of making a “User” in the Users & Groups pane of System Preferences.)

Recipe for Hosting a Presenter on Zoom

Here’s one way to have somebody who is not in the room teach a class or make a presentation to a live audience in the Classroom.

1. Turn on both of the Zoom Mac mini’s video displays, so that people on both sides of the presenter’s desk can see the Zoom screen.
2. Power up the projector
3. Select 3 on the Kramer. The Zoom Mac mini’s video should now appear on the projector; if not then debug.
4. Log into the Zoom Mac mini, either with your personal local account or the shared account “A Zoom User”
5. Make sound on the Zoom Mac mini. It doesn’t matter how: sound file, website, Zoom, etc. (The Mac mini sound should come out the built-in headphone jack, not via any HDMI or USB audio the machine might recognize.)
6. Turn up the “Zoom” channel on the mixer. You should hear the Mac mini’s sound; if not then debug.
7. Decide which local camera to send to Zoom and choose it on the “Drum Machine”. The front camera is the obvious choice, showing the faces of the audience. The rear camera is nice because it shows backs of audience heads as well as confirming that the people in the Classroom are seeing the right content on the projector. (The camera is good enough that projected content is generally legible even when seen through the camera.)
   
8. Ideally somebody in person in the Classroom will sit in front of the Zoom Mac mini to monitor chat, etc.

If/when the current presenter is local, it’s worth going through everything above, and then just make these few additions:

1. Select the local presenter’s computer video on the Kramer, possibly switching the local projection back and forth between that and the Zoom video on input 3 (like if somebody remote asks an involved question, or when going between local and remote presenters).
2. Use a microphone on the local presenter, either lav(alier) or handheld. The corresponding mute buttons on the mixer determine whether the mic will go to both zoom and the local loudspeakers (unmuted) or only to zoom (muted), depending on the local preference. (Skipping this step means using only the distant room mic: the zoom sound will be distant and reverberant, so that all but the loudest presenter voices will be inaudible over Zoom without headphones.)
3. Make sure the local presenter has computer sound through the mixer; if so then it should automatically go to Zoom. When playing sound examples, it’s best to use “Original Sound” type options (because to Zoom these are coming into the “microphone” that is actually our mixer, not via Zoom screen sharing with “share sound”). But if remote people are talking through Zoom through the local loudspeakers, you might want/need to turn off “Original Sound” to avoid feedback/echo.

Linux Machine

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

It shares a small keyboard and video display with the Mac Mini via a KVM switch.

Linux Audio

It currently has a Tascam 2x2 like most other CCRMA Linux Workstations, wired (in analog/stereo) to the mixer.

This page of CCRMA documentation last committed on Wed Jan 15 13:00:46 2025 -0800 by Matthew James Wright. Stanford has a page for Digital Accessibility.