SRS Uses SHARC for SRS Circle Surround® II Technology for Home Theater, PCs, Cars, Wireless Streaming
It used to be that surround-sound audio experiences were confined to movie theater settings. Then along came multi-channel encode/decode systems, which surrounded us with theater-quality sound in our own homes and tangled us in an array of wires, speakers, and amplifiers. With Circle Surround (CS) II encode/decode technology from SRS Labs, full multi-channel surround sound can be produced from media formats and A/V setups that previously could only deliver simple right/left stereo sound, without the need to purchase additional speakers/wires.
Based in Santa Ana, California, SRS develops and licenses a wide range of technology solutions for audio, voice, surround sound, and semiconductor applications. More than 500 million products have been shipped from the more than 200 licensees of SRS' technologies, including companies with household names in both electronics and software markets. The company's CS II is quickly becoming the standard for the creation, production, and broadcast of up to 6.1 discrete channels of surround sound over traditional two-channel distribution systems, including television commercials, sports broadcasting, network shows, cable and satellite transmissions, and standard music CDs.
CS decoding supports numerous product applications, including home theater, personal computers, automobile stereos, and wireless streaming, allowing people to take advantage of their multiple speaker system, including older VHS tapes, FM radio broadcasts, stereo music CDs, and computer games. To that end, SRS has partnered with leading analog and digital semiconductor companies and software providers to make the technology readily available for any product manufacturer. And, according to SRS' executive vice president (EVP) of technology and business development, Alan Kraemer, SHARC processors from Analog Devices, Inc. (ADI) are the ideal platform for CS II algorithms in both the pro audio and home entertainment markets alike.
How It Works
CS II encoding is a powerful and versatile tool for broadcasters and content providers who want to offer their audiences surround sound without making a substantial change to their infrastructure or distribution method. SRS tools for audio professionals include analog and digital processors, and plug-ins for widely used software platforms. Audio professionals can produce multi-channel audio content in CS II for distribution or storage over a standard two-channel medium such as broadcast television, radio, or regular CDs. It is also backward compatible with all playback environments, including mono, stereo, and other matrix decoders, such as Dolby Pro Logic and Dolby Pro Logic II surround systems. This flexibility assures broadcasters that their audience will receive the best sounding experience possible, subject only to the limitations of the consumer's particular decoder.
CS II Algorithms Explained
The encode algorithm works as follows. Input summing amplifiers A1 and A4 combine the main left and right signals with the center input and the low frequency effects (LFE) input (which accommodates very loud low frequency effects sounds, such as explosions). The output of the two amplifiers, which now contains the left, right, center, and LFE information, is then applied to constant phase filter banks F1 and F4 and passed to output summing amplifiers A5 and A6. Next, summing amplifiers A2 and A3 combine the surround back input with the surround left and right inputs. The output of these amplifiers is then fed to constant phase networks F2 and F3 to encode the surrounds in quadrature with the main channels (required to prevent signal cancellation).
The surround signals are then mixed antiphasically into the left/right output. In order to distinguish the left and right surround encoding, the left/right balance of the surround material is varied dynamically based on the predominance of the signal. A "surround positional bias generator" analyzes the ratio of the left and right surround signal level to produce steering signals. The steering signals are then applied to multipliers M1 and M2, which modulate the level of the surround mix into the opposing left or right output.
The CS II decoder makes use of this level imbalance in the out-of-phase surround material to "steer" the surround information left or right. Dual-band steering is utilized in the decoder to stabilize the surround steering and to minimize "pumping" effects between the surrounds. The CS II decoder algorithm also includes patented post-processing techniques that enhance the audio experience (such as bass performance) and address problems (such as dialog clarity).
Hardware manufacturers and software providers can license the CS II decoder to develop products that deliver up to 6.1 channels of surround sound from any audio material, including CS II-encoded content or mono, stereo, and other matrix surround formats. The two core versions available for license are: CS II for home theater, PCs, and wireless products; and CS Automotive, which mitigates the audio challenges that are unique to the automotive environment, including the placement of front speakers low in the door panels and rear speakers mounted facing away from listeners.
Both CS II solutions include two SRS patented post-processing techniques that enhance the surround sound experience: SRS Dialog Clarity, which improves the intelligibility of dialog, as it can often be difficult to hear it clearly over explosions, music soundtracks, and other sounds; and SRS TruBass, which works with any size speaker (without the need for a subwoofer), including headphones and earbuds, enabling listeners to perceive a heightened sensation of lower bass tones beyond the natural low frequency capabilities of the speaker itself.
SHARC Helps SRS "Multiply" Channels
Needless to say, the CS II algorithms are complex and require a processor that can handle sophisticated mathematical equations. "We needed an efficient signal processor that could implement audio filters and handle a lot of multiplication and division," says Kraemer. "ADI's 32-bit floating-point SHARC processor was an obvious choice. It's fast and efficient. A less efficient processor would get bogged down with the math. With SHARC, it was easy for us to port our patented audio algorithms. Plus we also found we could easily press the SHARC processor into service for general-purpose microprocessor functions, which it can handle in its spare time."
ADI's 32-bit floating-point SHARC processors are based on a Super Harvard architecture that balances exceptional core and memory performance with outstanding I/O throughput capabilities. In addition to satisfying the demands of the most computationally intensive, real-time signal-processing applications, SHARC processors integrate large memory arrays and application-specific peripherals designed to simplify product development and reduce time to market. The third-generation of SHARC processors, which includes SHARC ADSP-2126x and ADSP-2136x processors and the SHARC Melody, and Melody 32 platforms, offer increased performance, audio-centric peripherals, and new memory configurations that can support the latest industry-standard audio and surround-sound decoders and post-processing algorithms (which come with the processors on a factory programmed ROM).
The Right Audio Features
The SHARC processor's audio-specific peripherals, broadly described as the Digital Audio Interface (DAI), are functional blocks that may be connected to each other or to external pins via the signal routing unit (SRU). Peripherals connected through the SRU include as many as six high-performance, synchronous serial ports, SPI ports, an input data port (IDP), precision clock generators, timers, and others. The combination of the serial ports and IDP means that SHARC processors can support up to 20 stereo I2 channels, providing up to 40 channels of audio (which is important as the number of speakers and input sources is increasing in audio applications).
Additional value-added peripherals include an S/PDIF transmitter/receiver, 8-channel asynchronous sample rate converter, and hardware digital transmission content protection (DTCP) encryption/decryption block. Audio-specific peripherals such as these allow manufacturers to leverage a single hardware design for multiple products with various I/O requirements. "Architecturally, SHARC processors had all of the audio features we needed," says Kraemer. "SHARC processors support all of the standard audio in/out interfaces as well as easy analog-to-digital, digital-to-analog conversion."
VisualAudio is the new graphical audio system design and development environment that supports third-generation SHARC processors. It works as a plug-in for ADI's VisualDSP++ integrated development and debug environment, and streamlines the development of SHARC-based audio systems. System developers can reduce time-to-market, development risk, and development cost. Says Kraemer (who, as previously stated, is the EVP of technology and business development at SRS), "The SHARC platform is so easy to work with and coding is such a pleasure that I roll up my own sleeves and do some of it myself."
One of the most important reasons SRS chose ADI's SHARC processor, says Kraemer, is that it's the platform their customers want. And we're talking about leading manufacturers of professional and consumer audio equipment, such as Marantz, Kenwood, Theta Digital, and Accuphase. So whether you are a consumer who wants to hear full-bandwidth surround sound over your Windows Media Player or an audio professional looking for the most sophisticated digital surround sound broadcast encoder, SRS and ADI can provide the solution. Together, ADI's SHARC processors and CS II technology from SRS enable powerful hardware and software products that deliver multichannel surround sound over existing stereo carriers.
For more information about CS II, please visit SRS .