Seeing is Believing but Smart Surveillance Cameras Let You Speak and Listen Too!

By Neal Kurfiss and Michael Jackson 

The final blog in this series considers some of the advantages that audio can bring to this application and presents a convenient audio codec to manage the speaker and microphone signals. The previous blog in this series looked at the additional benefits of including radar sensors in surveillance cameras.

Advantages of Using Audio-enabled Surveillance Cameras  

While the primary purpose of a surveillance camera is to capture a visual stream of images, the benefits that audio can bring are sometimes overlooked. Some of the enhancements a high-quality audio system comprising a speaker and a microphone can offer include: 

• Improved security: Intruders are often aware of the position of surveillance cameras, which allows them to identify blind spots where they can’t be seen. However, if a surveillance camera is audio enabled, even though intruders can stay out of the visual frame, they can’t conceal their voices when they speak or the sound of their movements. This audio input can be used to alert the security personnel or smart-camera.  Audio can also be bi-directional as it can be used by security personnel to communicate directly with the intruders and warn them to leave the premises immediately or risk being apprehended.
    
• Better surveillance: The quality of video images captured by surveillance cameras has improved considerably in recent years to the extent that lip reading of conversations is now possible. This has resulted in would-be conspirators covering their mouths either using their hands or clothing. Audio-enabled cameras have the advantage of still being able to capture the content of these conversations which could potentially be used as evidence if a crime was committed.  
  
  
• Intelligent analytics: Sounds like breaking glass, screams and gunshots are typically associated with emergency events but these can sometimes be difficult for security personnel to discern from high levels of background noise. A high-quality audio feed from a surveillance camera can be processed using audio analytic software to detect the occurrence of these sounds and immediately bring them to the attention of security personnel who may have missed them. In the future, audio analytics will be used alongside video analytics to provide surveillance cameras the intelligence they need to operate autonomously, only alerting security personnel to events that need their attention. 
  
  
• Crowd Management: Large numbers of people at sporting or music events require careful monitoring to prevent localized overcrowding that can result in a dangerous crush or stampede in the event of a fire or crowd trouble. Using audio-enabled surveillance cameras allows event organizers to communicate directly with sections of a crowd that require directing to a specific location or exit to alleviate these dangers. 

Audio CODEC for Surveillance Cameras  

Analog Devices’ ADAU1361 (Figure 1) offers a convenient solution for providing surveillance cameras with two-way audio capability. This is a low-power, stereo audio codec that supports stereo 48 kHz recording and playback at 14 mW from a 1.8 V analog supply. The stereo audio ADCs and DACs support sample rates from 8 kHz to 96 kHz as well as a digital volume control. The ADAU1361 is ideal for battery-powered audio and telephony applications. The record path includes an integrated microphone bias circuit and six inputs. The inputs can be mixed and muxed before the ADC, or they can be configured to bypass the ADC. The ADAU1361 includes a stereo digital microphone input. The ADAU1361 includes five high-power output drivers (two differential and three single-ended), supporting stereo headphones, an earpiece, or other output transducers. AC-coupled or capless configurations are supported. Individual fine-level controls are supported on all analog outputs. The output mixer stage allows for flexible routing of audio. The serial control bus supports the I2C and SPI protocols, while the serial audio bus is programmable for I2S, left-/right-justified, and TDM modes. A programmable PLL supports flexible clock generation for all standard integer rates and fractional master clocks from 8 MHz to 27 MHz. 

Figure 1 Analog Devices' ADAU1361 audio codec

Summary 

This blog series has shown how surveillance camera applications are evolving and presented a suite of Analog Devices technology solutions to help camera designers keep up with these changes. Analog Devices' Trinamic drivers enable smooth, low-noise camera motor movement, while Single Pair Ethernet offers a convenient ‘2-in-1’ power and connectivity solution. A GMSL serial link enables new types of miniature multi-camera applications, while radar and audio provide cameras with extra senses for added intelligence. Click here for more information on Analog Devices’ security and surveillance solutions.