Extremely Low-latency, Bi-directional, Multi-channel Audio Using Software Define Radio (SDR)

Low-latency Wireless Audio Design

As a networked, pro audio product design company, Cardinal Peak is dedicated to helping brands bring their new audio products to market quickly. For networked, multi-channel, bi-directional 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.

One of the most challenging areas to achieve low latency is wireless systems since commercial wireless standards have significant and non-deterministic 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

 

We had a customer that needed an extremely low latency (sub millisecond) link for both wired and wireless 10 channel bi-directional audio. For the wireless solution, we developed a custom software defined radio (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 reason. First was the ready availability of an RF SOM with a FPGA of sufficient size 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 as 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 were:

  • 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 where 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 Related ADI and Professional Audio Experience


About Cardinal Peak’s Product Design Services

Cardinal Peak accelerates your product development with end-to-end design services for connected devices. A leading product engineering firm, Cardinal Peak leverages deep experience in hardware, embedded software, cloud, end-user applications, such as mobile, 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

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 has in virtually any live performance.

Why is Low Latency Challenging for Wireless Audio Systems?

Commercial wireless standards have been designed for playback of audio and 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 then 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 as there is no digitization step, error checking or other data processing techniques that improve quality but require time to process.


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