IP cameras are getting more and more sophisticated.  Many of the newer cameras include two-way audio, but what do you need to know to make the best use of audio capability?  This article answers the questions: What are the best cameras, microphones and speakers for the applications? How good is the audio and how do you use it?  How do you talk to many people or just one person?  How do you record the audio and what are the legal implications?  Here are the answers to all your questions.


 
Overview of Applications
Audio is great for certain applications. An IP camera system can be used in a visual intercom application. For example, the camera can be placed at a doorway and with an attached microphone and speaker allows you to communicate with a person somewhere else in the building (or even over the Internet).  You can even use the output IO from the camera to control a relay that unlocks a door.

 
IP cameras with audio have been used in interview or interrogation rooms. It provides a simple way to keep a record of what is seen and heard. In this case special software is required to store the audio with the video. 
 
Some people have even used an IP camera system to store and distribute presentations on the Internet. 
 
Be aware that there are certain state and federal laws that relate to recording audio (wire tapping), and in most cases require people to be notified they are being recorded.

Equipment
 
Cameras with Audio
In almost all cases a camera that includes audio, supports MPEG4 compression.  This form of compression includes data packets for audio transfer as well as video.   For example, the Axis 210A includes two-way audio.  It has audio input and audio output so you can attach a microphone and powered speaker.  Other cameras with audio include Axis214PTZ and Axis211A, Vivotek IP6112, Panasonic WV-NS202 and WV-NP244.
 
Here are more details about the Axis210A which includes support for two-way audio.

Axis210AL2
The AXIS 210A, indoor only camera with Computar 2.8-12mm manual focus, manual iris lens, delivers Motion JPEG images at up to 30 frames per second in all resolutions up to 640x480. With a built-in microphone and the ability to connect to external speaker or microphone, the AXIS 210A enables remote users to not only view, but also listen in on an area and communicate orders or requests to visitors or intruders.  Includes built-in motion detection, and provides both full frame rate Motion JPEG and MPEG-4 video streams simultaneously.  MPEG-4 compression mode is ideal for applications where available bandwidth is restricted and higher frame rates are required. Built-in Power over Ethernet allows the camera to receive both data and power over a single Ethernet cable.

 Microphones
Just like any application using audio, you have to consider how to pick up the sound. If you just use the microphone on the camera (some cameras have this included) you will pick up all the audio in the room, including noise you don’t want.  The microphone should be as close as possible to the person.

You can use many different kinds of microphones including handheld, wireless microphones and even directional room microphones. Just make sure the type of microphone matches input requirements of the camera.  Most of the cameras take “line level” type mics.  These line level microphones are similar to those used with audio components such as CD and DVD players, TVs, audio amplifiers and other consumer equipment.  Cameras usually accept the 3.5mm mono audio input connector. In some cases the microphone doesn’t have the right connector for the camera, but this can be corrected by using an adapter. 
 
General Microphone
If you just want to be able to hear a person at another location, you can use a standard microphone.  Just make sure the microphone cable has the right connector (usually mini-plug). To connect to the camera audio input. For example:

M951m
The Paso Professional hypercardioid mic is great for recording, studio, stage, vocal and PA. This is a rugged die-cast construction microphone with 50 – 18,000 Hz frequency response. Dual anti-pop windscreen and includes 15 ft. detachable cable with 3 pin XLR audio male connector at equipment end and carrying case.

Since this microphone has an XLR connector, you need to add a XLR plug to mini plug audio cable so it can be plugged into the camera.
 
Room Microphone for interrogation
Yes, we did say that a room microphone is not usually recommended, especially for large meeting rooms, but it will work in small interview or interrogation rooms. The Louroe omni-directional microphone can be used in this application.  This uses a very sensitive electret condenser omni-directional microphone. Since this type of microphone doesn’t provide the right electronic output signal, the package includes a pre-amp so it can be used with the camera.  The police like this for interrogation rooms. 
 
The following kit includes everything you need to pick up sound in a room.

ASK-4 Kit300
Single zone audio monitoring system designed for direct connection to a camera. Omni-directional microphone can pick up normal sounds 15’ away or within a 30’ diameter circle. Package includes the 3.5mm mono audio output required for a camera. A connector cable is also included. Distance between the Verifact A. Microphone and Model IF-1 Interface Adapter may be up to 1,000 ft. using recommended wiring.

 
There are many other microphones that can be used.  Contact me for some more recommendations.
 
Speakers
 
You can talk through an IP camera that has audio output.  Some cameras have built-in speakers, but in most cases you need an external powered speaker.  The speaker needs to be powered because the camera doesn’t have enough amplification power.  The cameras that support two-way audio have a 3.5mm mono audio output similar to the microphone input connection. I have seen some cameras with only one shared audio connection so be careful about this.  In this case you need to use a splitter that allows both a microphone and speaker to be connected.