Put Low-Power, Low-Overhead, High-Fidelity Digital Sound in Your Next ASIC or SOC

Put Low-Power, Low-Overhead, High-Fidelity Digital Sound in Your Next ASIC or SOC

High-quality audio creates an immersive experience that excites buyers and spurs the purchase of consumer products such as home theater and PC sound systems, flat-panel televisions, handheld and console video games, portable music and video players, and mobile telephone handsets. As a result, digital audio has rocketed to the top of the critical features list for all sorts of products over the past several years. At the same time, the number of digital audio codecs (coders and decoders) and audio-enhancement programs has exploded and most consumer products must support multiple codecs and offer a broad range of audio-enhancement features.

All of these factors have resulted in a high demand for a flexible, high-performance, low-power audio DSPs that add sound to an SOC's design with the least amount of design effort and a small on-chip footprint. Tensilica's HiFi Audio DSP family was carefully crafted to meet these requirements for the broadest possible range of consumer products. The HiFi 2 and HiFi EP Audio DSPs are available as an audio-extension packages for the Xtensa LX configurable processor core and the HiFi 2 DSP is incorporated into the pre-configured 330HiFi processor core.

Why use programmable SOC hardware for audio?

The ASICs developed for the original digital music players did not use programmable MP3 decoders. Instead, they used dedicated hardware because that approach resulted in the lowest gate count. However, for products that must handle multiple digital-audio codecs (and just play MP3 files), the need for multiple hardware codecs quickly increases gate count, making the use of hardware audio codecs quickly lose its advantages. For products that must support two or more digital-audio file formats, a programmable approach is far more attractive. Consequently, nearly all new ASIC and SOC designs incorporating digital audio employ some form of programmable engine to run the audio codecs.

In addition to supporting multiple audio codecs, the programmable design approach actually reduces design risk because future changes in one of the existing codec standards or in the product's definition can be accommodated through a firmware change instead of a hardware change, which would require a spin of the silicon. In addition, the programmable nature of a processor-based approach makes it far easier to add application-specific pre- and post-processing to the end product. Such features include sample-rate conversion, multi-band frequency equalization, speaker virtualization, and parsing (audio content extraction from a file using various container formats).

Why not just use a RISC processor or DSP for audio?

General-purpose processors are often used to implement audio codecs because these processors can do anything that can be expressed in a firmware program, given enough execution cycles. With a sufficiently fast clock, general-purpose processors can implement multiple audio codec algorithms and they are therefore suitable for multipurpose devices that must accommodate several digital-audio standards. However, general-purpose processors are not especially efficient engines for running audio codecs, which means that they must run at higher clock rates to deliver real-time, multichannel audio. In turn, the higher clock rates cause these processors to consume more energy than do processors with audio-specific instruction sets. Higher power dissipation presents a real problem for portable, battery-powered devices.

DSPs generally run audio codecs more efficiently than do general-purpose processors because they have features that accelerate the execution of audio-specific code such as hardware MACs. However, DSPs have specialized and irregular architectures that make them poor targets for C compilers and therefore, DSPs are not attractive as control processors. Consequently, DSPs are usually paired with a general-purpose control processor to create a design platform with sufficient capability and flexibility to be used for today's consumer products.