Extremely Low-Latency, Bidirectional, Multichannel Audio Using Software-Defined Radio (SDR)

Low-Latency Wireless Audio Design

As a networked, professional audio product design company, Cardinal Peak is dedicated to helping brands bring their new audio products to market quickly. For networked, multichannel, bidirectional pro audio solutions, latency is a major concern. Real-time applications, such as conferencing, live performance and interactive gaming, require low latency and consistent jitter so the audio feels natural to listeners and doesn’t cause cognitive jamming.

Achieving low latency in wireless systems is challenging since commercial wireless standards have significant and nondeterministic latency. From the table below, Bluetooth and 4G are not acceptable for low-latency audio designs. While there is potential for 5G and Wi-Fi, those systems introduce variable delays as networks become loaded. This variability is often a bigger problem than the absolute latency.

Typical Latency (ms) for Commercial Wireless Interface Standards

Wireless Interface Standard Typical Latency (ms)
Bluetooth 200
Bluetooth with Qualcomm AptX 40
4G Cellular 40-60
5G Cellular 1-4
IEEE 802.11ac Wi-Fi 1-1.5

Software-Defined Radio Audio Design Example

We had a customer that needed an extremely low-latency (submillisecond) link for both wired and wireless 10-channel bidirectional audio. For the wireless solution, we utilized our software-defined radio (SDR) audio expertise to develop a custom SDR with sub-ms latency using Analog Devices’ (ADI) Catalina transceiver. For the wired version, we used ADI’s A2B. The A2B wired and SDR wireless links were just one part of the overall networked audio system, which also leveraged Audinate’s Dante protocol for time synchronization as shown in the following figure.

SDR subpage figure1

We elected to use ADI’s Catalina transceivers for a couple of reasons. First was the ready availability of an RF SOM with a sufficiently sized FPGA to implement the radio along with an embedded ARM core to run Linux (Zynq). Second was the frequency agility, as we needed both 2.4 GHz and 5.8 GHz to accommodate data since our requirement was to be able to run multiple Catalina-based systems simultaneously. This frequency agility precluded existing solutions from companies such as Lime.

The challenges included the following:

  • Implementing the radio entirely in logic (FPGA) instead of software to meet latency requirements (see the following figure)
  • Designing a custom waveform
  • Could not use Wi-Fi or other commercial protocols because of latency issues
  • As we had a custom waveform, we could not leverage all the commercially available test tools for commercial protocols

In our implementation, all the modem processing was done in the FPGA instead of the microprocessors to improve throughput and lower latency as shown in the following figure.

SDR subpage figure2

While this project was implemented using Catalina, we see how the newer Navassa parts, with their lower bandwidth and lower power, will be well suited for pro audio wireless microphones. The lower bandwidth means that no FPGA will be required, so the radio could be implemented using a low-cost, low-power microprocessor. These same qualities also mean that Navassa is well suited for land mobile radio applications. Given Navassa’s new chip-to-chip phase synchronization capability, we also see some great applications in phased array applications, such as satellite tracking and radar.

Our ADI and Professional Audio Experience

About Cardinal Peak’s Audio Product Design Services

Cardinal Peak accelerates your audio product development with end-to-end design services. A leading product engineering firm, Cardinal Peak leverages deep experience in hardware, embedded software, cloud, mobile end-user applications and quality assurance to develop connected IoT products in multiple markets, including audio, video, security and medical.

  • Product Ideation: Developing differentiated products that disrupt markets
  • IoT: Designing products that integrate with mobile applications and cloud systems
  • Audio, Video & Mixed Reality: Unparalleled strength in media processing
  • Voice: Experts at embedding voice processing capabilities in connected devices
  • QA: From black box testing to test automation and manufacturing support
Cardinal Peak Product Design Services

FAQs About Low-Latency Wireless Audio Design

What is the difference between professional and consumer audio?

While fidelity can be a hallmark of professional audio, a common element in professional audio systems is the ability to manage many synchronous audio streams simultaneously, such as in virtually any live performance. The main difference between pro and consumer audio is not audio quality but instead the multichannel nature of professional audio applications. Consumer audio might be very high-quality audio, but consumer audio doesn’t involve managing tens to hundreds of synchronous audio channels over a network.

Why is low latency challenging for wireless audio systems?

Commercial wireless standards have been designed for playback of audio. As such, the protocols were not written to minimize latency. When designing wireless audio systems, it is often not possible to leverage existing tried-and-true commercial standards, so the effort is greatly increased. Additionally, many of these systems require multichannel audio, and that audio needs to be tightly synchronized.

What is the difference between analog and digital wireless audio?

For digital wireless audio, the audio signal must first be digitized before it is sent (like other digital data, with data checks and retries to fix any errors). Analog audio is the straight audio signal sent over RF like in AM or FM transmission with amplitude or frequency modulation. Digital audio provides all the same benefits that are common for digital systems, including collision recovery, error checking, encryption and more. Analog audio is still used in many places, as it is easier to minimize the latency because there is no digitization step, error checking or other data processing techniques that improve quality but require time to process.

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