Real-time, wireless audio streaming is a technology that can serve in applications from the living room, to mobile applications, to automotive infotainment. Designing streaming audio applications requires balancing range, complexity of implementation, costs, and realized performance. Wi-Fi is ubiquitous and affords great range but is not ideal for low-latency real-time streaming. Bluetooth® can handle the real-time application and adds the robustness of an industry standard protocol and multivendor support but has range limitations. Other proprietary systems can deliver the required performance with less complexity, albeit without the multivendor support.
There is a broad range of applications for streaming digital audio data over wireless links. Consumers today enjoy music delivered over wireless cellular networks and perhaps further distributed around a home via Wi-Fi. Applications can extend into industrial settings where multimedia data is delivered to rugged systems. Furthermore, wireless audio is prevalent with portable devices via Bluetooth and in automotive infotainment to link wireless headphones.
Design teams looking to stream audio wirelessly have a lot of choices in how to implement such capabilities. There are many options and application requirements using LAN and PAN (personal area network) with varying transmission range.
Wi-Fi, defined by the IEEE 802.11 family of standards, is the most prevalent wireless technology within homes and businesses. The popularity of Wi-Fi has driven large manufacturing volumes for Wi-Fi ICs and in turn driven implementation costs lower than predicted.
The implementation complexity of Wi-Fi also has been minimized by the availability of modular turnkey implementations for design teams that are not comfortable working at the IC level. For example, Digi-Key offers easy-to-integrate Wi-Fi modules from more than a half dozen vendors.
With cost mitigated, and complexity removed as an obstacle, Wi-Fi is a good choice in many audio applications such as media players that connect to the Internet. However, Wi-Fi can suffer from latency and synchronization problems, especially for real-time applications like streaming audio to wireless speakers that are synchronized with video displayed on a TV. The TCP/IP protocol can add tens of milliseconds in latency to each packet depending on the performance of the packet processor. Moreover, network congestions could delay the sending of an audio packet for even longer periods. Additionally, Wi-Fi has no isochronous capability to synchronize audio and video playback.
Bluetooth provides one-to-one link
Bluetooth, conversely, provides a one-to-one link between two devices and doesn’t suffer the latency issues associated Wi-Fi. Bluetooth has been broadly deployed in streaming wireless applications. For example, TV makers such as Vizio have built Bluetooth into interactive TVs and supplied companion Bluetooth stereo headphones. Logitech has delivered an adapter that connects with any audio output and wirelessly transmits audio to paired Bluetooth headphones.
Design teams considering Bluetooth have many choices for implementation including working at the IC or module level. Digi-Key stocks modular Bluetooth products from more than a dozen vendors.
The depth and product range of such offerings available from manufacturers, such as CSR, is vast. For example, CSR offers a broad range of ICs, modules, and development kits. The latest BlueCore6 family is targeted primarily at cellular headsets. The BlueCore5 family is optimized for high-end multimedia applications.
The BlueCore5 architecture features an integrated DSP along with dual integrated data converters – two ADCs and two DACs – for stereo audio applications. The IC can encode audio with sampling rates as high as 44.1 kHz providing CD-audio quality. The BlueCore5 provides both the requisite wireless connectivity and the ability to support popular audio codecs such as MP3 and AAC.
CSR has also developed a number of development kits that can accelerate wireless audio product designs. For example, both the BlueCore5 Multimedia Development Kit (Figure 1) and the BlueTunes2 Development Kit, support audio applications and are based on BlueCore5-family ICs. The kits also include a reference design for wireless headphones or speakers and support experimentation with a broad range of digital and analog audio formats.
Figure 1: The CSR BlueCore5 Multimedia Development kit includes a reference design that supports projects such as wireless speakers and headphones and leverages the stereo capabilities and data converters integrated on the BlueCore5 IC.
Implementing wireless audio with Bluetooth offers a number of advantages, most importantly is multivendor support. If you develop a Bluetooth-enabled product – whether it’s a device that streams audio outbound or receives audio and plays the stream – the product will work with devices from other vendors.
Proprietary wireless schemes
Bluetooth, however, is complex and can be costly. Bluetooth inherently requires a microcontroller (or other processor) to handle the Bluetooth software stack. Moreover, programming a Bluetooth IC to perform the desired application may require a significant software-development effort, although that is mitigated by development kits.
Proprietary approaches to wireless audio can certainly result in a simpler design effort, although the simplicity results in a less-feature-rich product. For those applications that mandate lower cost and complexity, Texas Instruments (TI) offers its PurePath wireless audio technology.
PurePath uses the same 2.4-GHz frequency band used by Bluetooth but does not require a programmable processing element and TI’s ICs are purpose-built for linking devices such as stereo receivers or TVs to wireless speakers or headphones.
The TI CC8520 system-level block diagram in Figure 2 depicts the simplicity. You can connect the IC directly with an audio output and the IC handles the wireless streaming task with only a minimal amount of discrete support components.
Figure 2: Texas Instruments CC8520 PurePath IC can connect directly to an audio source with minimal external components, and wirelessly stream CD-quality stereo audio to speakers or headphones.
The PurePath IC can be used alongside DSPs, microcontrollers, codecs, amplifiers, data converters, and other ICs. However, those functions aren’t required to implement the wireless functionality in a system. The IC implements what TI calls CD-quality audio with sampling rates as high as 48 kHz. TI also plans to offer a new version of the IC that includes USB support to allow design teams to easily add audio transmitters to any USB-equipped product.
TI offers a comprehensive PurePath Wireless Development Kit (Figure 3) to help designers shorten the learning curve. Moreover, TI also has published a reference design.
Figure 3: The TI PurePath Wireless Development Kit includes the CC8520 IC and offers a jump-start to designs that use the wireless audio technology.
Wireless audio can provide a significant value-add to audio-based projects. Carefully consider your application requirements and you will likely find a wireless scheme that matches your cost requirements and offers the feature set demanded by the application.