Sophisticated soundscapes usher in cache-coherent multicore DSP

Digital audio processing is evolving into an art form, particularly in high-end applications such as automotive, cinema, and home theater. Innovation is moving beyond spatial audio technologies to concepts such as environmental correction and spatial confinement. These sophisticated soundscapes are driving a sudden increase in digital signal processing (DSP) performance demands, including the use of multiple DSPs and AI inference in applications. The degree of difficulty in programming multiple DSPs for coordinated audio processing has outweighed the benefits – until now, with the introduction of a cache-coherent multicore DSP solution. Cadence’s Prakash Madhvapathy, Product Marketing Director for HiFi DSP IP, spoke with us about what is changing and how cache-coherent DSPs can unlock new applications.

Sounds that fill – or don’t fill – a space

Spatial audio schemes enable each sound source to possess unique intensity and directionality characteristics, and multiple sources can move through the same space simultaneously. The result can be a highly realistic, immersive 3D experience for listeners in a pristine environment. “Ideally, you’d be able to create your listening environment, say for a soundbar, or headphones, maybe earbuds, or your car,” says Madhvapathy. “You might want to enhance sources, or reduce or remove them altogether.” (For instance, in my home, we have a Bose 5.1 soundbar without a subwoofer because my wife has heightened bass sensitivity.)

Few listening spaces are pristine, however. “Noise can take multiple forms, and they are not always statistically static; they keep changing,” Madhvapathy continues. There can be keyboard clicking, other conversations, traffic noise, and more noise sources. Noise reduction is becoming increasingly complex because what’s noise to one listener might be an important conversation to another, both of whom are hearing sounds in the same space. “Traditional DSP use cases can deliver some noise reduction, but AI is evolving to handle more complex reduction tasks where sources are less predictable than, say, a constant background hum.” AI may also play a role in adapting sound for the space, handling dead spots or reverberations.

High-end automotive sound processing is also becoming much more sophisticated. Some of the latest cars deploy as many as 24 speakers to create listening zones. What the driver hears may be entirely different from what a passenger hears, as cancellation technology provides spatial confinement for the sound each listener experiences, or “sound bubbles” as Madhvapathy affectionately refers to them. “The complexity of different zones in a vehicle can make it difficult to update all of them when using distributed audio processing,” he observes. “The other problem is concurrency – music, phone calls, traffic noise reduction, conversation cancellation, everything has to happen simultaneously and seamlessly, otherwise sound quality suffers for some or all listeners.”

Low-power, high-performance DSPs built on mature cores

Audio processing demand is skyrocketing, and Cadence has turned to a familiar, yet strikingly new solution to increase DSP performance. “Previously, we were able to add performance to one of our HiFi family of DSPs and create enough headroom for customers to meet their audio requirements in a single processor,” says Madhvapathy. “Suddenly, customers are asking for four, six, or eight times the performance they had in our previous HiFi generations to deal with new DSP and AI algorithms.” Multicore has evolved from a DSP architecture that most designers avoided to one that is now essential for competing in the high-end audio market.

The latest addition is the Cadence Tensilica Cache-Coherent HiFi 5s SMP, a symmetric multiprocessor subsystem built on top of their eighth-generation Xtensa core, with additional SIMD registers and DSP blocks incorporated. “Cache-coherence is not a new concept in computer science by any means, but it’s now taking shape in DSP form with the HiFi 5s SMP,” he continues. “Overbuying cores is a problem when attempting hard partitioning of an application across cores, which rarely turns out to be sized correctly. With the HiFi 5s SMP, there’s a shared, cached memory space that all cores can access, and cores can scale up or down for your needs, so there is less wasted energy and cost, and programming is far easier.”

Audio applications gain more advantages. Microphones and speakers can tie into a single processing block with the right amount of DSP cores and memory. The HiFi 5s DSP cores offer multi-level interrupt handling for real-time prioritization of tasks running in FreeRTOS or Zephyr. They also accommodate power management, including three levels of power shut-off options and clock frequency scaling.

Madhvapathy concludes with a couple of interesting observations. While short life cycles are familiar in consumer devices like soundbars and earbuds, he’s seeing a drastic shortening of life cycles in automotive audio design, with features refreshed every two or three years to remain competitive. Scalability and cache coherence not only make software more straightforward, but they also simplify testing and reduce failures, with fewer instances of cache-related anomalies that don’t appear until designs are in the field and customers are dissatisfied.

Designers are just beginning to imagine what is possible in these sophisticated soundscapes, and the arrival of more DSP performance, along with ease of programming and scalability, is timely.

Learn more online about the Cadence Cache-Coherent HiFi 5s SMP for high-end audio processing:

News: Cadence Launches Cache-Coherent HiFi 5s SMP for Next-Gen Audio Applications
Product page: Cache-Coherent HiFi 5s Symmetric Multiprocessor
White paper: Cache-Coherent Symmetric Multiprocessing with LX8 Controllers on HiFi DSPs