Advances in video streaming and image rendering technology have greatly improved the quality of high definition (HD) moving images. Coupled with the growing popularity of home entertainment centers, these factors have become an important driving force in the pursuit of "home theater" experiences and the development of portable electronic devices. In addition to high-definition video, high-definition audio (HD Audio) has also been introduced to add a richer audio experience to the expanding multimedia entertainment world. This article will introduce the three major areas of the HD audio market, namely
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◠Digital TV – DTV
◠Set-top box – STB
â— Blu-ray DVD
According to the latest report, it is estimated that by 2011, the sales volume of DTV, set-top box and Blu-ray DVD will reach 187 million, 160 million and 116 million respectively. In addition, other market segments such as A/V receivers, HD camcorders, IPTV and mobile phones will also grow significantly.
However, there are significant differences between SD and HD audio specifications in terms of processing requirements, audio channels, bit rate and accuracy requirements. The many new requirements of high-definition audio systems not only affect all aspects of integrated circuit (IC) design, but also pose significant challenges for these new devices to achieve high-quality audio.
This article introduces a variety of high-definition media distribution technologies, explores the design challenges faced by IC designers, and proposes solutions and setup methods for efficiently implementing high-definition audio.
Figure 1 7.1 placement of the speaker system
HD Audio Application Opportunities The following are three major application opportunities for HD audio.
1 Digital TV (DTV)
Digital television (DTV) uses discrete (digital) signals to transmit and receive moving images and sound. The transition from analog TV to digital TV began in the late 1990s, and because it offered a full range of new business opportunities, it quickly became a high-profile technology in the television broadcast and consumer electronics industries. In the early countries adopting DTV, the Netherlands and Finland completed the analog-to-digital conversion in 2006 and 2007 respectively; and from June 12, 2009, all domestic TV stations will only use digital mode to broadcast programs. On the other hand, the UK has begun to convert to DTV and is scheduled to fully implement DTV broadcasting in 2012. The Chinese side plans to complete the conversion to DTV broadcasting by 2015.
A major challenge in the transition from analog to digital broadcasting or playback is the data processing and data traffic required for high-definition audio applications. For any IC-based HD audio solution to be successful, this needs to be taken into account during the development and implementation phases. Another challenge for DTV is the need to reduce the cost of the consumer, because the transition to DTV is mandatory, and consumers must replace the new TV with regulatory decisions, so they are very price sensitive.
2 set-top box (STB)
A set-top box (STB) is a device that connects a television to an external source and converts the signal into content that can be displayed on the TV screen. Digital set-top boxes can help digital TV broadcasts without the built-in digital tuner. In direct broadcast satellite systems, the set top box is an integrated receiver/decoder.
In markets such as the US, as analog broadcasting will end in 2009, audio quality is a focus of set-top box manufacturers to ensure that audio signals have quality that matches the video output.
3 Blu-ray Disc Blu-ray Disc (also known as "Blu-ray" or "BD") is an optical disc storage medium. The name Blu-ray comes from the fact that this disk format uses blue laser (actually purple-blue) for reading and writing, mainly for high-definition video and data storage. Since the beam wavelength (405 nm) of a Blu-ray disc is much shorter than the wavelength (650 nm) used for standard DVD encoding, its data storage amount is much larger. A standard dual-layer Blu-ray disc can store up to 50GB of data, which is almost 6 times more than a dual-layer DVD and 10 times higher than a single-layer DVD.
In an important announcement in February 2008, Toshiba indicated that it has withdrawn from the HD-DVD player and video recorder business. So far, the CD format between the HD-DVD camp represented by Toshiba and the Blu-ray disc camp represented by Sony has been fought. Finally the dust fell. This makes Blu-ray a leading multimedia HD recording medium. There are currently about 1,000 movies in various languages ​​distributed on Blu-ray Disc, and after the format war between HD-DVD and Blu-ray camps, the market expects this number to increase significantly.
The mandatory Blu-ray format audio codec Blu-ray format specification defines two sets of codecs that can be implemented in a Blu-ray player. The first of these is mandatory and must be used as the primary audio channel for Blu-ray Discs. These codecs include:
◠DTS – a multi-channel digital surround sound format for consumer applications such as commercial/cinema applications and video games.
◠Dolby Digital or AC-3 – a codec that can hold up to six discrete audio channels with a maximum encoding bit rate of 640kb/s, while 35mm motion picture film uses a fixed rate of 320kb/s, DVD Video discs are limited to 448 kb/s.
◠Linear PCM – an uncompressed audio format with a sampling frequency of 48 kHz or 96 kHz, 16, 20 or 24 bits per sample, for up to 8 audio channels. The maximum bit rate is 6.144MB/s.
Optional Audio Codec for Blu-ray Format The optional audio codec for Blu-ray format includes lossy and lossless codecs. Lossy codecs include:
◠Dolby Digital Plus – an AC-3 based enhanced lossy codec that supports bit rates up to 6.144 Mb/s and 7.1 audio channels. It also provides more advanced coding techniques, reduces compression artifacts, and is backward compatible with existing AC-3 hardware.
◠DTS HD High Resolution Audio – a lossy codec that extends the original DTS format and supports 7.1 channels at 96 kHz and 24-bit depth resolution. DTS-HD high-resolution audio provides a constant bit rate of up to 6.0Mb/s.
Lossless codecs are available:
◠Dolby Digital TrueHD – an HD multi-channel audio codec primarily used in high-definition home entertainment devices such as Blu-ray Disc. The maximum coding bit rate is 18 Mb/s (uncompressed rate). This has shown the high data traffic requirements for HD audio.
◠DTS-HD Master Audio – formerly known as DTS++ or DTS-HD, is an extended version of the original DTS codec. This is a lossless audio with a variable bit rate of up to 24.5Mb/s and supports 7.1 kHz discrete channels with 192kHz sampling frequency and 24-bit signal resolution.
Blu-ray HD Audio Use Case A computationally intensive Blu-ray use case for HD audio consists of main audio and sub audio streams, and an effects stream. The main audio stream can be combined with DTS-HD main audio (see the Blu-ray Disc section above) or Dolby TrueHD 7.1 channel for playing discs. The sub-audio stream can be DTS-HD Express or Dolby Digital Plus for additional data, such as a director's raise in a movie downloaded from the Internet. The sound stream is a simple PCM audio stream that adds sound to the on-screen menu.
The encoded stream can use a DTS 5.1 encoder or a Dolby Digital 5.1 encoder, and the encoding must transmit the data in a compressed format to a compatible audio/video receiver (such as via an S/PDIF cable). The mixed signal may require post-processing functions before being sent to the speaker to compensate for the sound mismatched playback environment or various audio incompleteness.
Figure 2 5.1 coding system
Design Challenges for HD Audio ICs There are several factors to consider when designing HD audio ICs. The most important feature of HD audio is data traffic, because HD audio data traffic is greatly improved compared to traditional audio applications. For I/O only, this data traffic can reach an input rate of 24.5 Mb/s at some codecs and 96 kHz x 8 x 24 bits per second at an output rate of 27.6 Mb/s. This requires a new IC design to ensure that these challenges are addressed while maintaining the quality of the audio.
In addition, some lossless audio codecs with a sampling frequency of 192 kHz, with 6 or 8 channels and high precision, such as DTS-HD main audio or Dolby TrueHD, are extremely computationally demanding. If not improved, a single codec may consume the full MHz budget of a traditional DSP.
Performance Requirements As mentioned above, high-definition audio implementations (such as Blu-ray Disc applications) require very high data processing. At such high data rates, many existing single-core DSP solutions cannot guarantee high-quality data processing. Therefore, many solutions in the industry have begun to adopt a dual-core solution that can meet the processing overhead requirements of video-combined audio.
Moreover, in the implementation of DSP solutions, in addition to mandatory and optional audio codecs, a lot of post-processing functions are required, and these post-processing functions are the differentiating factors of many implementations. Since many single-core DSPs are overloaded when dealing with the smallest HD audio codecs, there is little residual capacity, and even if they are, they are almost all used for mandatory post-processing.
Chip Size/Power Considerations As manufacturers and designers have to deal with the challenge, all the necessary processing functions are plugged into smaller and smaller chips, which puts enormous pressure on existing chip sizes. While multi-core solutions can provide these processing capabilities, the trade-offs between chip size, corresponding price increases, and the power required to drive subsystems can often be prohibitive. This is especially critical when it comes to meeting the requirements of high-definition devices (such as portable game consoles) with special power and form factor limitations.
Even for non-mobile devices, power consumption is an important consideration because it affects the thermal performance of the device. Higher power consumption may require some cooling means, which affects the overall design of the product.
Task-switched memory switching High-definition audio systems must perform a large number of parallel tasks, requiring very frequent memory swaps. These exchanges inevitably overload the memory bandwidth, making the system unable to handle the increased bus traffic and ultimately reducing the sound quality. In addition, because the instruction set is often written in a 32-bit format, which in turn makes the instructions larger and the intervals between instructions longer, further exacerbating the data overload problem, and the 16-bit instruction set can alleviate this load. In terms of data, some HD audio codecs require more than 100Kb of data RAM plus a fairly large data table, which is mandatory to use memory swapping to efficiently utilize RAM memory.
Slow External Memory Access Many audio algorithms running on DSPs have traditionally accessed large buffers in a non-sequential manner. In general, these caches are too large to reside in the on-chip memory of the processor, so they must be placed in slower external memory, such as DDR SDRAM. In addition, non-sequence access also poses a challenge to maintaining high performance goals. Since audio decoders often compete with video decoders for data bus throughput, memory access efficiency is very important. To provide a high-quality audio experience, you must solve this problem to achieve stable performance.
Solving the Problem To solve many of the problems affecting the high-definition audio DSP field, a system based on a powerful digital signal processor should be included, which should include appropriate software and peripherals. CEVA-HD-Audio is an example of this high-definition audio system, a comprehensive single-core DSP solution that meets the most demanding HD audio use cases.
CEVA-HD-Audio is a system based on the CEVA-TeakLite-III DSP core. The CEVA-TeakLite-III has native 32-bit processing power and a Multiply-Accumulate (MAC) architecture, making it an ideal DSP solution for high-definition audio applications requiring advanced audio standards. In addition, CEVA-TeakLite-III also has a well-balanced 10-stage pipeline, allowing its core to operate at frequencies exceeding 550MHz in 65nm process (under worst-case conditions and processes). CEVA-HD-Audio integrates a native 32-bit SIMD DSP processor with a 32-bit register file, 64-bit data storage bandwidth, 32 x 32-bit multiplier, and automatic 32-bit saturation. CEVA-TeakLite-III also features a dual 16 x 16 MAC with a complete MAC instruction set for voice/VoIP and full stream-manipulation, which is useful for stream processing. In addition to the inherent 32-bit data processing with multiple precision points, the single-cycle 32-bit MAC unit includes 72-bit MAC accumulation for lossless codecs, and unique single-precision and double-precision FFT butterfly instructions (butterfly) Instruction), as well as a 2/4 cycle kernel.
Figure 3 CEVA TeakLite-III block diagram
The CEVA-TeakLite-III architecture embeds the CEVA-Quark instruction set and is a comprehensive stand-alone embedded compact instruction set architecture (ISA). This unique ISA is designed to reduce chip size and cost with only 16-bit instructions while reducing power consumption and reducing memory accesses. The CEVA-Quark ISA is a complete set of instructions, including memory access, arithmetic and multiplication operations, logic, shift and stream processing bit manipulation instructions, and control operations. Application developers can also mix CEVA-Quark commands with other more advanced CEVA-TeakLite-III commands without having to switch to different modes of operation. This combination of features reduces code size by a factor of four and reduces the number of cycles by a factor of nine.
Using a single core to achieve high-performance HD audio processing efficiency mentioned above, CEVA-TeakLite-III can easily provide complete HD audio support with a single-core DSP. Because it has smaller memory, it is smaller in size and higher in performance, and is superior to other competing solutions on the market. The single-core implementation also means that application development and integration is easier, both from a hardware and software perspective.
Local audio processing
CEVA-HD-Audio has 32-bit local processing capability, so it can provide high precision for high-definition audio algorithms. In addition, the 64-bit data memory bandwidth ensures that the DSP continues to have data samples and coefficients fed in for continuous processing. To meet these challenges, the CEVA-HD-Audio solution also comes with a complete audio codec. The audio codec algorithm is designed using a common DMA engine that enables data transfer and algorithm execution to be performed in parallel, facilitating audio algorithms and codec processes. In addition, CEVA-HD-Audio includes a storage subsystem with instruction cache, tightly coupled memory for data, and AHB/APB system interfaces (both primary and secondary). These features help CEVA-HD-Audio users meet the stringent requirements of complex audio use cases, high latency for external memory access, and limited system speed. They are also easy to integrate into CPU-based SoCs for fast throughput improvements in complete audio systems.
High-definition audio software development A complete set of software development tools including C compilers, assemblers, linkers, code libraries, debuggers, and emulators is also important because they help users quickly and easily develop systems and integrated. A GUI-based development environment also allows programmers to easily follow different processing flows and improve the efficiency of programming, compiling, and debugging processes.
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