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 for the pursuit of "home theater" experience and the development of portable electronic devices. In addition to high-definition video, high-definition audio (HD Audio) is also introduced, adding a richer audio experience to the expanding multimedia entertainment world. This article will introduce the three major areas of the high-definition audio market, namely
â— 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 units respectively. In addition, other market sectors such as A / V receivers, high-definition camcorders, IPTV and mobile phones will also grow substantially.
However, there are significant differences between standard definition and high definition audio specifications in terms of processing requirements, audio channels, bit rate and accuracy requirements. The many new requirements for high-definition audio systems not only affect all aspects of integrated circuit (IC) design, but also bring major challenges to the realization of high-quality audio for these new devices.
This article will introduce various high-definition media distribution technologies, discuss the design challenges faced by IC designers, and propose solutions and setup methods for efficiently implementing high-definition audio.
Figure 1 7.1 Placement of the speaker system
High-definition audio application opportunities
Here are three main application opportunities for high-definition audio.
1 Digital TV (DTV)
Digital television (DTV) uses discrete (digital) signals to transmit and receive moving images and sound. The conversion from analog TV to digital TV began in the late 1990s, and because it provides a full range of new business opportunities, it quickly became a high-profile technology in the television broadcasting and consumer electronics industries. In the early countries that adopted DTV, the Netherlands and Finland completed the analog-to-digital conversion in 2006 and 2007, respectively. In the United States, from June 12, 2009, all domestic television stations will only use digital mode to broadcast programs. On the other hand, the United Kingdom has begun the transition 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 converting from analog to digital broadcasting or playback is the data processing and data traffic required for high-definition audio applications. For any IC-based high-definition audio solution to be successful, this needs to be taken into account in the development and implementation stages. Another challenge for DTV is that the cost of consumers must be reduced, because the conversion to DTV is mandatory, and consumers must replace new TVs in accordance with regulations, so they are very price sensitive.
2 Set-top box (STB)
A set-top box (STB) is a device that connects a TV to an external signal source and converts the signal into content that can be displayed on the TV screen. Digital set-top boxes can help TV sets without a built-in digital tuner to receive digital TV broadcast programs. In a direct broadcast satellite system, the set-top box is an integrated receiver / decoder.
In markets such as the United States, since analog broadcasting will be terminated in 2009, audio quality has become the focus of set-top box manufacturers to ensure that the audio signal has a quality that matches the video output.
3 Blu-ray disc
A Blu-ray disc (also called "Blu-ray" or "BD") is an optical disc storage medium. The name Blu-ray comes from the fact that this disk format uses a blue laser (actually purple-blue) for reading and writing, and is mainly used for high-definition video and data storage. Since the wavelength of the light beam of the Blu-ray Disc (405nm) is much shorter than the wavelength used for standard DVD encoding (650nm), its data storage capacity is also much larger. A standard double-layer Blu-ray disc can store up to 50GB of data, which is almost 6 times more than a double-layer DVD and 10 times higher than a single-layer DVD.
In an important announcement in February 2008, Toshiba announced its withdrawal from the HD-DVD player and recorder business. At this point, the disc format war between the HD-DVD camp represented by Toshiba and the Blu-ray disc camp represented by Sony Finally the dust fell. This makes Blu-ray one of the leading multimedia high-definition recording media in one fell swoop. There are currently about 1,000 movies in various languages ​​distributed on Blu-ray discs, and after the format war between the HD-DVD and Blu-ray camps is over, the market expects this number to increase substantially.
Mandatory Blu-ray format audio codec
The Blu-ray format specification defines two sets of codecs that can be implemented in Blu-ray players. The first set is mandatory and must be used as the main audio channel for Blu-ray discs. These codecs include:
â— DTS-a multi-channel digital surround sound format for consumer applications such as commercial / theater applications and video games.
â— Dolby Digital or AC-3-a codec that can hold up to 6 discrete audio channels, with a maximum encoding bit rate of 640kb / s, while a 35mm movie film uses a fixed rate of 320kb / s, DVD Video discs are limited to 448kb / s.
â— Linear PCM-an uncompressed audio format with a sampling frequency of 48kHz or 96kHz, 16, 20 or 24 bits per sample, which can accommodate up to 8 audio channels. The maximum bit rate is 6.144MB / s.
Optional audio codec in Blu-ray format
Optional audio codecs in Blu-ray format include lossy and lossless codecs. Lossy codecs include:
â— Dolby Digital Plus-an enhanced lossy codec based on AC-3, which can support bit rates up to 6.144Mb / s and 7.1 audio channels. It can also provide more advanced encoding technology, reduce compression distortion (compression arTIfact), and be backward compatible with existing AC-3 hardware.
â— DTS high-definition high-definition audio-a lossy codec that can extend the original DTS format, supporting 7.1 channels with 96kHz and 24-bit depth resolution. DTS-HD high-resolution audio can provide a constant bit rate of up to 6.0Mb / s.
Lossless codecs are:
◠Dolby Digital TrueHD – a high-definition multi-channel audio codec mainly used for high-definition home entertainment devices (such as Blu-ray discs). The maximum coding bit rate is 18Mb / s (uncompressed rate). This has shown the high data traffic requirements of HD audio.
◠DTS-HD main audio – previously known as DTS ++ or DTS-HD, it 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 discrete channels with a sampling frequency of 192kHz and 24-bit signal resolution.
Blu-ray HD audio use case
A computationally intensive Blu-ray use case for high-definition audio includes main audio and sub audio streams, as well as an effects stream. The main audio stream can be combined with DTS-HD main audio (see the previous Blu-ray Disc section) or Dolby TrueHD 7.1 channel for playing discs. The sub-audio stream can use DTS-HD Express or Dolby Digital Plus to obtain additional data, for example, the director ’s annotation in a movie downloaded from the Internet. The audio stream is a simple PCM audio stream that adds a choice of audio effects to the on-screen menu.
The encoded stream can use DTS 5.1 encoder or Dolby Digital 5.1 encoder, and the encoding must transmit the data in a compressed format to a compatible audio / video receiver (eg via S / PDIF cable). Mixed signals may require post-processing functions before being sent to the speakers to compensate for sound mismatches in the playback environment or various audio incompleteness.
Figure 2 5.1 encoding system
High-definition audio IC design challenges
There are several factors to consider when designing high-definition audio ICs. The most important feature of high-definition audio is data traffic, because compared to traditional audio applications, high-definition audio data traffic is greatly increased. As far as I / O is concerned, this data flow may reach an input rate of 24.5Mb / s and a output rate of 96kHz & TImes; 8 & TImes; 24 bits per second at an output rate of 27.6Mb / s in some codecs. This requires a new IC design solution to ensure that these challenges are resolved, while ensuring the quality of audio.
In addition, some lossless audio codecs with a sampling frequency of 192kHz, 6 or 8 channels, and high calculation accuracy, such as DTS-HD main audio or Dolby TrueHD, have extremely high calculation requirements. If it is not improved, a single codec may consume the entire MHz budget of a traditional DSP.
Performance requirements
As mentioned above, the data processing requirements of high-definition audio implementation solutions (such as Blu-ray Disc applications) are very high. At such a high data rate, many existing single-core DSP solutions cannot guarantee high-quality data processing, so many solutions in the industry are beginning to adopt dual-core solutions that can meet the processing overhead requirements of video combined with audio.
Moreover, in the implementation of DSP solutions, in addition to mandatory and optional audio codecs, many post-processing functions are required, and these post-processing functions are the differentiating factors of many implementation solutions. When dealing with the smallest high-definition audio codec, many single-core DSPs will be overloaded, so there is little remaining capacity at all, even if it is, it is almost used for mandatory post-processing.
Chip size / power consumption considerations
Because manufacturers and designers have to deal with the challenge, all the necessary processing functions are packed into smaller and smaller chips, which puts huge pressure on existing chip sizes. Although the use of multi-core solutions can provide these processing capabilities, the trade-offs between chip size, corresponding price increases, and power required by the drive subsystem can often be prohibitive. This is especially critical when 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 device's thermal performance. Higher power consumption may require some cooling methods, which will affect the overall design of the product.
Memory swap for task switching
In high-definition audio systems, a large number of parallel tasks must be performed, so very frequent memory exchanges are required. These exchanges will inevitably overload the memory bandwidth, make the system unable to handle the increased bus traffic, and eventually reduce the sound quality quickly. In addition, because the instruction set is often written in 32-bit format, which makes the instruction larger and the interval between instructions longer, further exacerbating the problem of data overload, and the 16-bit instruction set can reduce this load. In terms of data, some high-definition audio codecs require more than 100Kb of data RAM plus a large data table, which is mandatory to use memory swap to efficiently use RAM memory.
Slow external memory access
Many audio algorithms running on DSPs traditionally access large-capacity 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 a slower external memory, such as DDR SDRAM. In addition, non-sequential access also poses a challenge to the goal of maintaining high performance. 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, this problem must be solved to achieve stable performance.
Solve problems
To solve many problems affecting the field of high-definition audio DSP, a system based on a powerful digital signal processor is needed, which should include appropriate software and peripherals. CEVA-HD-Audio is an example of such a high-definition audio system. It is a comprehensive and complete single-core DSP solution that can meet the requirements of the most demanding high-definition audio use cases.
CEVA-HD-Audio is a system based on CEVA-TeakLite-III DSP core. CEVA-TeakLite-III has local 32-bit processing power and a double multiply-accumulate (Multiply-Accumulate, MAC) architecture. It is an ideal DSP solution for high-definition audio applications that require advanced audio standards. In addition, CEVA-TeakLite-III also has a well-balanced 10-stage pipeline, so that its core operating frequency under 65nm process still exceeds 550MHz (in the worst condition and process). CEVA-HD-Audio integrates a local 32-bit SIMD DSP processor with 32-bit register files, 64-bit data storage bandwidth, 32 × 32-bit multipliers and automatic 32-bit saturation. CEVA-TeakLite-III also has a dual 16 × 16 MAC with a complete MAC instruction set, which can realize voice / VoIP and comprehensive stream processing bit operation (bit-manipulation) function, which is very useful for stream processing. In addition to the inherent 32-bit data processing with multiple precision points, the single-cycle 32-bit MAC unit also includes 72-bit MAC accumulation for lossless codecs, and unique single-precision and double-precision FFT butterfly instructions (butteRFly instruction), and a 2/4 cycle core.
Figure 3 CEVA TeakLite-III structure block diagram
The CEVA-TeakLite-III architecture embeds the CEVA-Quark instruction set, which is a comprehensive independent embedded compact instruction set architecture (ISA). This unique ISA aims to use only 16-bit instructions to reduce the size and cost of the chip, while reducing power consumption and memory access times. 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 instructions with other more advanced CEVA-TeakLite-III instructions without switching to different operating modes. This combination of features can reduce the amount of code by 4 times and the number of cycles by nearly 9 times.
High-performance HD audio using a single core
The processing efficiency mentioned above shows that CEVA-TeakLite-III can utilize a single-core DSP to easily provide complete high-definition audio support. Because it has smaller memory, it has a smaller size and higher performance, which is better than other competing solutions on the market. The single-core implementation also means that application development and integration are easier from a hardware or 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 continuously feeds in data samples and coefficients, enabling continuous processing. To meet these challenges, the CEVA-HD-Audio solution also has a complete set of audio codecs. The audio codec algorithm design uses a common DMA engine to enable data transfer and algorithm execution to proceed in parallel, helping the audio algorithm and codec process. In addition, CEVA-HD-Audio also includes a storage subsystem with instruction cache, tightly coupled memory for data and AHB / APB system interfaces (including master and slave interfaces). These features help CEVA-HD-Audio users to meet the stringent requirements of complex audio use cases, high latency of external memory access, and limited system speed. They are also easy to integrate into CPU-based SoCs, which can achieve rapid output increase of complete audio systems.
HD Audio Software Development
A complete set of software development tools including C compiler, assembler, linker, code base, debugger and emulator is also very important, because they can help users develop and integrate the system quickly and easily. A GUI-based development environment also allows programmers to easily follow different processing processes, improving the efficiency of programming, compilation, and debugging processes.
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