Using the audio features of the 211A will require attaching powered speakers to its audio out jack (Figure 12) and a microphone and speakers (or PC headset) on the computer accessing its web interface. And, as I've mentioned above, you'll need to be using Internet Explorer as a web browser.
Figure 12: Axis 211A connected to two Bose powered speakers
The 211A supports two audio channels between it and web-based clients - one for receiving and one for transmitting audio - using either the G.711 PCM codec @ 64 kbits/sec or G.726 ADPCM codec @ 32 or 24 kbits/sec. Each audio channel can be turned on or off, which means that there are four audio mode options (plus audio disable):
This mode is similar to using a telephone - you and the remote party can talk and listen at the same time, without having to use the "push to talk" controls
Transmits and receives audio in both directions, but in only one direction at a time. This means that you select when to receive or transmit audio by using the microphone icon on the ActiveX toolbar
Simplex - speaker only mode
The powered speaker connected to the 211A will play audio, but no audio will be transmitted from the AXIS 211A to other web clients
Simplex - microphone only mode
Transmits audio from the 211A to web clients, but will not receive audio from web clients
Figure 13: Configuring the audio settings
(click image to enlarge)
The 211A also has advanced audio controls including a speech filter and noise and echo cancellation.
Axis claims that up to 10 people can simultaneously listen to an audio stream when the camera is in full-duplex mode. I didn't test that limit, but was able to test up to three simultaneous listeners with no loss in audio quality - which was excellent.
In contrast to the excellent received audio quality, I judged "talk" quality to be only acceptable, with a fair amount of static audible in the background. As with video, Axis doesn't bundle a way to record audio to or from the camera. So you'll need to either purchase Axis' pro-level (and priced to match) AXIS Camera Recorder software, or use third-party software.
While being able to talk to an intruder may seem like a novelty at first, it can help prevent crime. Traditionally, cameras have passively recorded thefts, which helps in prosecution after a crime has been committed. This is great, but you have to endure the hassle of filing a police report and waiting for your stuff to be returned. Why not instead stop intruders in their tracks by directly letting them know with your own voice that they are being watched?