Advantages of the latest audio formats are apparent for silicon, software, and technology providers; system manufacturers; and media producers. But benefits for consumers are less obvious. Couple that with the formats' diversity and incompatibility, and they all may end up as niches. Listen up.

With high-resolution formats (those with sample sizes larger than 16 bits, sample rates higher than 48 kHz, or both), the audio industry hopes it's concocted the secret sauce that'll get consumers buying again. The pitches sure sound alluring: 24-bit samples, 192-kHz and 2.822-MHz sampling rates, and the like. The PC industry has historically used an analogous bigger-numbers-are-better pitch to sell (and upsell) consumers on its latest and greatest, most expensive microprocessors and the computers containing them. But, as the PC industry has lately discovered, there's an upper-end price threshold beyond which, especially in the absence of compelling applications, customers aren't willing to travel.

Will music aficionados refresh their collections with high-resolution versions and purchase the more expensive (and not coincidentally, copy-protected) high-resolution variants of new tunes they acquire, if their ears and brains can't discern a significant-enough difference from good, old Red Book audio CDs? (See sidebar "Signal to noise: calculating the high-res-audio reality-to-hype ratio.") And will they rush out to buy new players, receivers, and speakers if surround sound, not ultrasonic sound, is the compelling new feature, and their existing gear will therefore suit them just fine? Ironically, these questions come just a few months past the 20th anniversary of the first CD-player sales in Japan. Recent trends don't give encouraging answers.

Warner Brothers recently announced plans to lower its DVD-Audio disc prices to CD-like levels. Do you think the company planned to make this drastic a price cut this soon, when it first decided to enter the DVD-Audio market years ago? DVD-Audio player prices, near $1000 just one year ago, are now less than $150 at retail. Granted, for suppliers, this situation is an improvement over the $50 DVD-Video players crowding store shelves. But who thought DVD-Video players would be at $50 this quickly? DVD-Audio isn't the only victim; SACDs (Super Audio CDs) and their players are close behind in price, and hybrid SACD-plus-DVD-Audio players have already dipped below $500 (see sidebar "Seeking soothing sounds").

Anticipated customer acceptance and the price at which you'll achieve that acceptance are important issues to consider when designing your next audio-augmented system. Extra features invariably add cost, but if you can't recover that cost (and, ideally, earn a profit) with a higher price tag, you're in trouble. Which of the format contenders have the greatest chance for commercial success and why? When will that success happen and in which applications will it occur—professional audio, high-end or mainstream home audio, car audio, or portable audio? The auditions are open, and the contestants have arrived. Let's listen in and rate their performances.

Pacific Microsonics was perhaps the first company to develop a high-resolution audio technology that achieved broad industry adoption. HDCD (High Density Compatible Digital) audio builds on industry-standard audio-CD and -DVD foundations (Figure 1). By embedding control information within the altered LSBs (least significant bits) of, on average, less than 5% of the formats' stored audio samples, the developers claim that HDCD can dramatically expand the audio's dynamic range if the playback device contains an HDCD-aware decoder. Otherwise, the altered LSBs take the form of uncorrelated noise, analogous to dither and are effectively inaudible.

The substance behind HDCD's "20-bit" marketing sizzle takes three primary forms. First, HDCD encoding dynamically selects, as music characteristics vary over time among four anti-alias FIR (finite-impulse-response) filters with different characteristics between 16 and 22 kHz. The intent, in balancing frequency rejection and transient response, is to make the filter act as sonically neutral as possible over a wide range of possible audio conditions. Some of the LSB control bits drive a corresponding configurable filter array at the HDCD decoder.

Other HDCD control bits extend peak levels as much as 6 dB beyond the normal 16-bit audio limits, via a compress-on-encode-and-expand-on-decode mechanism that conceptually works similarly to Dolby and other noise-reduction systems. Likewise, the remaining HDCD control bits extend low levels as much as 7.5 dB below an audio CD's dynamic-range bottom end. After reading the company's documentation and applying the 6.02-dB-per-bit rule of thumb, it's still unclear how HDCD marketers can claim 20-bit results, versus the slightly more than 18-bit dynamic range that peak- and low-level extension would imply.

When considering the DVD-Video format as a high-resolution audio-storage platform, some folks forget that they don't necessarily need to resort to lossy-compression schemes, such as Dolby Digital or DTS (Digital Theater Systems). It's possible to shoehorn at least two, and as many as six, high-resolution audio channels within DVD-Video's 6.144-Mbps maximum-allowable audio bit rate (Table 1). Given, though, that most DVD-Video discs (as the name implies) hold image-plus-sound presentations, that high video bit rates are critical to acceptable image quality, and that both filmmakers and viewers value the flexibility of multiple audio-track options within the stream (representing different languages, audio formats, and other qualities), lossy audio compression dominates the DVD-Video scene.

Dolby Digital compression delivers a 48-kHz sample rate, a "claimed" 20-bit dynamic range, and a 5.1-channel (five full-range and one for low-frequency effects) audio presentation via a 384- to 448-kbps bit rate (Reference 1). Because many of the formats that this article discusses from this point on are "lossy" (perceptual) in nature, perhaps it's time to elaborate on the "claimed" qualifier in the preceding sentence, which applies not only to Dolby Digital. A perceptual encoder might accept, for example, a 24-bit, 192-kHz sampled input, and its corresponding decoder might spit back out a 24-bit, 192-kHz stream. But who's to say what audio information the intermediary compressed file has preserved?

Perceptual encoders will, after all, discard audio information they judge to be inaudible to listeners (references 2 to 4). An encoder could decide, to achieve a certain overall level of quality at a target bit rate, to throw away the dynamic range potential beyond 16 bits (96 dB, or 93 dB if LSB-dithered) or to filter out the two octaves' worth of information beyond 48 kHz, because "nobody can hear it anyway." This decision is pragmatic and by no means an inappropriate trade-off, especially at aggressive bit-rate targets.

DTS's Coherent Acoustics lossy-compression scheme, Dolby's primary surround-sound competitor on DVD-Video, creates a 1.5-Mbps or 768-kbps compressed bit stream with a claimed 24-bit dynamic range at a 48-kHz sampling rate. DTS compression also appears on audio CDs at 1.234 Mbps, with 20- or 24-bit dynamic range and a 44.1-kHz sampling rate. Unlike HDCD, DTS audio CDs aren't backward-compatible with the Red Book audio-CD format, so decoders that aren't DTS-aware will output audio that sounds like the hiss of random noise.

The DTS bit-stream format was, from the very beginning, designed for future extensibility, with corresponding backward compatibility to prior-generation decoders. The company, for example, uses this extension mechanism to add another channel's worth of data in the DTS-ES Discrete 6.1 format. It also finds use in storing the extra octave's worth of frequency information in the DTS 96/24 format. The first number in the name suggests a 96-kHz sampling rate. DTS 96/24 takes the difference between the 48- and 96-kHz signals, compresses it, and sends it in an optional field, which a first-generation decoder ignores (Figure 2). DTS 96/24-aware decoders sum the fields to recreate a semblance of the original audio.

With DVD-Audio, the entire 9.6-Mbps bit stream is available, if desired, for audio information. This higher bit rate enables the media to store two channels of 24-bit, 192-kHz uncompressed audio. The bit rate is not, however, high enough to enable the uncompressed transfer of six channels' worth of 24-bit, 192-kHz or, for that matter, even 96-kHz surround audio. Numerous ways to get around this limitation exist. You could reduce the sampling rate or sample size of all channels. Thanks to the flexibility built into the DVD-Audio specification, you can also selectively reduce the sampling rate or sample size of only some of the channels; they need not all have the same characteristics. Consider, for example, a channel carrying primarily vocals (center), reverberation effects (surrounds), or low-frequency information (subwoofer), and the bit-slimming techniques possible in such cases.

The third option involves the use of MLP (Meridian Lossless Packing), which as its name implies was developed by Meridian Audio. Unlike most other high-resolution audio-compression algorithms this article discusses, MLP is lossless (Reference 5). In most cases, MLP in conjunction with buffering will enable six-channel, 24-bit, 96-kHz audio storage (normally requiring a 13.8-Mbit bit rate) to fit within DVD-Audio's peak transfer-rate envelope (Table 2). Lossless-compression ratios depend on the source-media entropy characteristics, though, so there are no guarantees—you'll need to test the process yourself.

MLP also provides a means by which you can extend the per-disc playback time (Table 3). Its use on DVD-Audio discs is optional, but its presence on DVD-Audio bit-stream decoders is required. DVD-Audio format standardization is by no means complete; the DVD Forum is, for example, finalizing specifications for DVD-AR (DVD-Audio Recordable). DVD-AR reportedly comprehends not only linear and packed (MLP-encoded) PCM (pulse-code-modulated) audio, but also six lossy formats: Dolby Digital, DTS, MPEG-1 (and MPEG-2) Layer II, ATRAC-3, MP3PRO (a backward-compatible superset of MP3), and MPEG-2 AAC (Advanced Audio Coding).

Because DVD-Audio discs can contain DVD-Video partitions, many record labels also put Dolby Digital- or DTS-encoded versions of the audio in these partitions for backward compatibility with legacy players. Many record labels also embed Verance-developed watermarking information within the otherwise-pristine DVD-Audio data, using a perceptual technique analogous to the one that lossy compression employs. Although the watermarking is not so invasive as to create objectionable audio, ABX comparative testing reveals that it is audible under some circumstances (Reference 6).

Watermarking differences are among the least significant of the variations between DVD-Audio and SACD. The brainchild of CD pioneers Philips and Sony, SACD employs a physical, rather than perceptual, watermark that therefore doesn't alter the audio characteristics. Although many first-generation SACDs delivered only two-channel audio, an increasing number of discs contain surround-sound mixes, and many SACDs are multilayer hybrids that also work on CD players—albeit in a 16-bit, 44.1-kHz two-channel fashion (Figure 3).

Whereas DVD-Audio builds on the multibit PCM data-storage approach first employed on CDs, SACD switches to a single-bit 2.822-MHz-sampled PDM (pulse-density-modulation) scheme called DSD (direct stream digital), which works in conjunction with MLP-like lossless compression. Philips and Sony claim that, by bypassing the decimate-while-recording and oversample-during-playback stages in PCM-based audio, SACD delivers a higher quality result. Ironically, though, SACD still employs multibit PCM-like techniques during the mixing and mastering stages of most discs' creation process. This decision was probably driven by a desire for compatibility with today's computing hardware and software that, after all, best handles information when it's clustered in multibit groups.

The last several AES (Audio Engineering Society) conventions have been jam-packed with papers debating both the absolute and the relative merits of DVD-Audio and SACD. Predictably, many of the presentations come from company representatives with vested interests in the formats, such as those of Derk Reefman, who works for Philips Research Laboratories. Some of them, though, derive from independent, usually academic, sources, such as Professor Malcolm Hawksford from the University of Essex, UK, and Professors Stanley Lipshitz and John Vanderkooy from the University of Waterloo, Canada.

These AES presentations are overwhelmingly critical of SACD, noting shortcomings such as its inability to dither the single-bit data stream, the nonlinearities that DSD subsequently creates, and the incapacity of noise shaping to fully move these artifacts out of the 20- to 20,000-Hz frequency range. Although the presenters acknowledge that the levels of these distortions are likely so low as to make them inaudible, they point out that similar distortions do not exist with the alternative PCM approach. The counterarguments offered by SACD proponents, such as Professor James Angus of the University of Salford, UK, are, in my estimation, insubstantial in comparison.

If SACD is an inferior high-resolution format, as these and other audio pundits claim, then why did the Sony/Philips alliance introduce it instead of joining the rest of the industry in supporting DVD-Audio? The answer, in a word, is money. Philips and Sony have greatly benefited from the success of the CD format and the licensing revenues that this success has generated. In DVD, they saw the seeds of CDs' likely eventual demise, and they therefore created SACD as a proprietary competitor, fueled by both companies' considerable consumer electronics muscle and by Sony's synergistic status as a music producer. Ironically, at least for the moment, SACD is the healthier of the two formats, thanks to the aggressive media rollout strategy that Sony Music and its affiliate labels employ. When any of the format alternatives is "good enough," consumers will buy whichever one delivers the artists they prefer.

Turning your attention to streaming media, you should first be aware of the 24-bit MP3 decoders L3Dec and MAD (MPEG Audio Decoder). They claim to reduce the distortion caused by rounding approximations in traditional 16-bit MP3 decoders, and you can either play the results unaltered on a 24-bit-capable sound system or dither them down to 16-bit versions. The MAD plug-in for Winamp is perhaps the easiest way to explore the concept for yourself; a HEX-to-WAV transcoder for L3Dec is also available. Mindful of the diverse sample sizes and sampling rates that the heir-apparent AAC specification encompasses, the Fraunhofer Institute presented a paper on 24-bit, 96-kHz AAC compression at the December 2001 AES Convention in New York City.

Microsoft's WMA (Windows Media Audio) Professional is the new kid on the block in high-resolution audio. The company adapted its base WMA codec to handle as many as eight audio channels along with larger-than-16-bit sample sizes and greater-than-48 kHz sampling rates. WMA has undergone numerous quality-improving revisions during its brief life and is currently at version 9. Two-channel WMA (WMA Consumer) encoders create bit streams compatible with decoders stretching all the way back to version 2. Similarly, Microsoft hopes to "freeze" the WMA Professional bit stream at this initial version, so consumer-electronics customers can embed the necessary decoding hardware and software without fear of future obsolescence.

Just how large a bit stream WMA Professional requires is a matter of some ambiguity. The documentation Microsoft initially sent me suggested an encode bit rate of 384 to 700 kbps. When, not realizing that the literature already answered my bit-rate question, I again asked Microsoft for the information, the company provided the same 128-kbps-minimum-bit-rate response that it recommends for 16-bit, 44.1-kHz surround material. Asking the question a third time, for clarification, I learned that whereas 128 kbps would deliver six channels of audio, the quality for all but the least demanding material would be subpar compared with DVD-Audio or SACD.

Amir Majidimehr, Microsoft's General Manager for Digital Media comments, "It is generally true that as you increase the sample rate, the data rate should also go up to maintain the same level of distortion. However, this trend is usually for sample rates [of] less than or equal to CD's 44.1 kHz. It is unclear that distortion above 22.05 kHz is very audible. That is, as [you] go up to 96 kHz at the same data rate, there is bound to be more distortion at ultrasonic frequencies. But it appears, in [Microsoft's] testing, anyway, that such distortion is not as audible as the distortion created, say, when going from 22.05-kHz sampling to 44.1 kHz."

"The same is also true when you go from 16-bit to 24-bit [audio]," he continued. "Few systems, if any, can reproduce signals more accurately than 20 bits. So again, distortions in the least significant 4 bits may not be audible, and in fact they might even help to dither the DACs. The other key thing to consider is that one of the main benefits of using higher sampling rates is to encode the original high-quality digital master without resampling, not necessarily to preserve high-frequency information that people may or may not hear."

For most music, 192-kbps (variable-bit-rate) or 256-kbps (constant-bit-rate) encoding is sufficient, according to Microsoft. And for critical listening tests on challenging audio sources, the originally submitted estimates should suffice. Even 384 kbps is impressive, though, when you consider that it's half the bit rate of the lowest of the two DTS 24-bit, 48-kHz, 5.1-channel encode options, and roughly one-fourth the bit rate of a two-channel, 16-bit, 44.1-kHz Red Book audio CD's PCM stream. WMA Professional has obvious application in streaming-media delivery environments, but when you pair it with Microsoft's version 9 video codec, it also opens the door to intriguing digital-cinema and red-laser-friendly high-resolution DVD scenarios (references 7 and 8). Microsoft acquired Pacific Microsonic's HDCD technology in late 2000, adding yet another weapon to its high-resolution-audio arsenal.

Audio, like any other human-sensory-input mechanism, is inherently an analog medium, both as it travels toward microphones during capture and as it travels out of transducers during playback. But, with the exception of the enduring cassette tape, all of today's prevalent audio-storage and -distribution mediums are digital: CDs and DVDs, DAT (digital audio tape) and Minidiscs, along with AAC, MP3, RealAudio, WAV, WMA, and other file formats. Clearly, some conversion is going on, both to (with ADCs) and from (with DACs) the digital domain, as well as within (with SRCs, or sample rate converters) to bring all of the incoming digital data to a common sample rate prior to tackling mixing and other audio-processing functions.

Peruse the myriad ADC, DAC, ADC-plus-DAC (codec), and SRC options available from companies such as AKM Semiconductor, Analog Devices, Cirrus Logic, Texas Instruments, and Wolfson Microelectronics, and you may walk away with a severe headache. A tremendous diversity of alternatives exists; one obvious differentiator is the number of integrated channels. You'll also discover that a few decibels' difference in claimed dynamic range or THD (total harmonic distortion) plus noise, both inside and outside the audible frequency range, can significantly affect the price you'll pay (Figure 4). First, though, you'll need to ask yourself if you even believe the vendors' specs (references 9 and 10).

An ADC might integrate one or multiple S/PDIF (Sony/Philips Digital Interface) transmitters. A DAC might include S/PDIF receivers, global or per-channel digital volume control, or the capability to directly interact with both multibit PCM and single-bit (SACD) inputs. A direct path from the SACD decoder to the DAC saves you from the added expense; the additional board space; and the audiophile purists' wrath that a separate SACD-to-PCM transcode chip, such as Nippon Precision Circuits' SM5816AF would create. Keep in mind when evaluating your options that for DVD-Audio, only two channels have to support 192-kHz sampling rates.

For practical purposes, ask yourself just how wide the dynamic range and how low the THD plus noise really need to be, given that the codec is just one piece of an audio-processing chain that's constrained by its weakest link. How high is the quality of the speakers that consumers will likely hook up, directly or indirectly, to this piece of equipment? How much degradation will occur through equipment interconnect? What kind of music will the average user listen to? And, perhaps most importantly, what are the characteristics of the anticipated listening environment?

Will your target customer be auditioning audio while sitting still in a pin-drop quiet anechoic chamber, or inside his or her car in the garage late at night with the engine off? Or will the system you design be playing background music at dinner parties with attendees milling about, be reproducing mostly dialogue and explosions for home theater, compete with an open window and jabbering front- and back-seat passengers on the open road, or inhabit the hazardous environment endured by a PC internal sound system?

Some examples from recent Cirrus Logic press releases may enlighten you to the many trade-offs you face. In October 2001, Cirrus quoted the CS4362 six-channel DAC at $5.35 (10,000), and priced the CS4382 8-channel DAC at $6.50. In May 2002, Cirrus priced the CS5361 ADC, with differential inputs, 114-dB dynamic range, and 105-dB THD plus noise at $4.95 (10,000). The pin-compatible CS5351, with single-ended inputs, 108-dB dynamic range, and 100-dB THD noise was $3.95. Combine channel and spec choices, and the decision becomes even more complicated, as Cirrus's latest product-family announcement reveals (Table 4). All of the vendors slice and dice their product lines in a similar manner. It's up to you to balance trade-offs and pick an option that works best in your situation.

Larger chunks of audio data, flowing into and out of the system at faster rates, make correspondingly greater demands on the processing subsystem. Estimates of the number-crunching needed to decode DTS 96/24, for example, start at 25 MIPS (according to DTS, on the Analog Devices 21065L 32-bit floating-point SHARC DSP) and can rise far above that figure, reflecting DSP-architecture variations (such as the 32-bit integer processing in Analog Devices' Melody 32 DSPs), the use of high-level, inefficient languages to code the algorithms, and other factors. Factors other than a DSP's clock rate are also critical in determining its performance; the amount of embedded memory, for example, is also key. Every time the DSP exceeds the capacities of internal RAM and ROM and must access much slower external memory, sustained performance will suffer.

The emergence of 24-bit audio has fueled the long-running debate over 24- versus 32-bit processors. Pragmatically, as long as you have enough time to do the necessary multipass calculations and enough memory to hold interim data, any processor data width will adequately perform the job you require of it without creating an adverse amount of truncation- and overflow-caused rounding error. Time, though, is of course the limiting factor; listeners won't long tolerate nonreal-time audio processing! The wider the internal data path (extending to the adoption of floating-point capability), the fewer the passes the algorithm must make through the DSP. Similarly, the greater the amount of onboard hardware acceleration, the more work the processor can do in each clock.

This trend reaches its peak (of impressiveness or ludicrousness—take your pick) with Texas Instruments' TMS320DA610 audio DSP, the first member in the company's Aureus line. TI claims that the DA610, which runs at 225 MHz, delivers a mind-boggling 1800 MIPS and 1350 Mflops of performance. How did TI come up with those astronomical numbers? Under certain conditions, the DA610 can execute as many as eight instructions within a single clock. TI doesn't have an exclusive on this feature, though. As one of its competitors points out, it's possible for many vendors' DSPs to simultaneously execute multiple operations. For example, the following three parallel operations:

1. mac x0,y0,b
2. x:(r0)+,x0
3. y:(r4)+,y1

break down into the following seven "atomic" instructions:

1. multiply x0 and y0
2. add result to b
3. move x:(r0) to x0
4. increment r0
5. move y:(r4) to y1
6. increment r4
7. round result of multiplication

Will you always achieve 1800-MIPS performance in the DA610? Of course not. You probably won't even consistently achieve 225 MIPS of processing muscle, for reasons such as the earlier-described external memory bottleneck. Regardless of the vendors' claims, you need to make sure there's always enough overhead to handle not only the audio-decoding functions but also various postprocessing tasks, including bass management and other types of speaker compensation, THX adjustments, and surround-sound speaker virtualization. If you run out of gas and you're using a traditional single-core DSP architecture, such as Analog Devices' SHARC line, Motorola's DSP5636x DSPs, or TI's DA610, you'll need to incorporate a second DSP in your design and allocate functions between the two processors, which is never a simple task.

Alternatively, Cirrus Logic's CS49400 is, all by itself, a dual-core DSP. The CS49400 walks a middle path in the 24- versus 32-bit debate. A 24-bit processor handles decoding, a separate 32-bit DSP handles post-decode functions, and the partitioned DTS 96/24 algorithm splits between the two processors. Motorola recommends the DSP56311 or DSP56321, with their EFCOP (Enhanced Filter Coprocessor) cores, as companion chips for its main DSP5636x audio DSPs. An upcoming revision of the DSP56367, code-named Onyx, will boost both the amount of on-chip memory and the clock speed of today's Motorola chips, the latter to a 180-MHz target. Motorola also plans to increase the speed of its EFCOP-inclusive DSPs to 180 MHz.

All of the aforementioned processors tend to find homes in home-theater receivers and other high-end gear. Eventually, these DSPs will probably be directly decoding DVD-Audio and SACD bit streams, just as they decode Dolby Digital and DTS streams today. Until the interconnect quagmire—which this article will later explore—gets straightened out, though, the optical disc players are responsible for this task. DVD chip sets from companies such as Cirrus Logic, STMicroelectronics, and Zoran are already handling DVD-Audio-targeted functions, such as watermark detection, digital-rights-management decryption, and MLP decoding. SACD processing currently takes place in a separate Sony-sourced chip. But if the format achieves widespread popularity, and the IC vendors obtain licenses from Philips and Sony, SACD functions will also become integrated as another in a long line of simplification steps so critical in cost-sensitive, consumer-electronics applications.

High-resolution audio support is increasingly appearing in mainstream PCs, not just in high-end machines for professional use. Until the AC'97 specification and silicon undergo another revision, 20-bit, 48-kHz, six-channel audio and 20-bit, 96-kHz, two-channel audio define the upper-end limit for codecs, such as those by SigmaTel. Higher bandwidth PCI-, USB-, and IEEE-1394-based boards and external peripherals fulfill today's ultrasonic audio needs. Creative Labs' THX-certified Audigy 2 line, based on the company's Emu processors, handles the generation of 6.1-channel audio (DTS-ES, Dolby Digital EX, and others); the decoding of DVD-Audio's full range of sample sizes and rates; and recording at 24-bit, 96-kHz quality.

Via Technologies' acquisition of IC Ensemble in late 2000 gave it 24-bit, 96-kHz (with the Envy24 processor) and 24-bit, 192-kHz (with Envy24HT) capability, of which numerous third-party sound-card manufacturers are taking advantage. Note that while 6× and faster DVD-ROM drives will play DVD-Audio discs when partnered with an appropriate audio subsystem and software, such as InterVideo's upcoming upgrade of Win-DVD 4, no solution currently exists for playing SACDs on the PC, aside from the legacy audio-CD layer on "hybrid" discs. Perhaps that topic will be the next one that Project Bar-B-Q tackles (www.projectbarbq.com).

Clarifying connections

At the moment, six-channel analog interfaces are the only means of connecting most DVD-Audio and SACD players to home-theater receivers. This low-tech reflection of record-label demands for copy protection burdens the system with disabled bass management and other consumer-unfriendly implementation quirks (references 11 and 12 ). If a player’s S/PDIF output is active when reading a DVD-Audio disc or SACD, the player likely also downmixes and down-
samples the audio to two-channel, 16-bit, 44.1-kHz quality. Even the Audigy 2, operating in the notoriously open PC environment, behaves and disables its S/PDIF outputs when playing DVD-Audio discs. Meridian Audio offers a proprietary digital player-to-receiver high-resolution audio interconnect it calls MHR (Meridian High Resolution) Smart Link; Denon’s Digital Link incorporates the “4C” CPPM (Content Protection for Prerecorded Media) and CPRM (Content Protection for Recordable Media) schemes and employs RJ-45-connector-based cabling.

DTCP (Digital Transmission Content Protection), the so-called “5C”-enhanced IEEE-1394A interconnect, which receives support from chips such as Texas Instruments’ TSC43CA43A, is an emerging industry-standard means of digitally, bidirectionally transporting high-resolution audio between devices. The TSC43CA43A integrates a three-port PHY and supports multiple audio formats (IEC 60958, IEC 61937, multibit linear raw audio, DVD-Audio, and SACD) and multiple audio interfaces (S/PDIF, I²S, and adaptive PCM). IEEE-1394A enables interdevice control and communication in addition to raw data transfer, and 400-Mbps bandwidth is sufficient to carry both high-resolution audio and compressed video, for subsequent decoding at the destination. Pioneer showcases the TSC43CA43A in its latest DVD-plus-SACD “hybrid” player.

IEEE-1394A, though, delivers insufficient bandwidth to handle uncompressed video, especially in the emerging DTV era (references 13 and 14). Home-theater receivers commonly tackle audio-decoding tasks. By centralizing this function, you can eliminate redundant DACs and ADCs (and the quality losses associated with interim analog transformations) and reduce the processing complexity and therefore the cost of connected peripherals. However, asking A/V receivers to also take on multiformat video decoding, a much more strenuous task than the simple switching among various video inputs that they already do, may be unrealistic. The first iteration of IEEE-1394B, at 800 Mbps, still doesn’t deliver enough bandwidth for multichannel high-resolution audio plus uncompressed high-definition video, although future 1.6- and 3.2-Gbps IEEE-1394 variants will fit the bill. For the near term, therefore, IEEE-1394 might reduce the amount of cabling in a system over analog-centric approaches, but it doesn’t take cabling to its bare minimum.

Enter DVI. This 5-Gbps per-link unidirectional protocol, originally developed as a digital video interconnect between PCs and displays, encompasses limited bidirectional communication and control through the integrated DDC (Display Data Channel) interface. It has been enhanced in several key areas to broaden its functions and, therefore, possible applications. First, the DDWG (Digital Display Working Group) added copy-protection capabilities in the Hollywood-blessed form of HDCP (High-bandwidth Digital Content Protection). More recently, several competing schemes for securely appending audio to the copy-protected video stream have been unveiled: DVI-HDMI (High Definition Multimedia Interface), formerly known as PanelLink A/V from Silicon Image, and an alternative proposal from Broadcom, Genesis Microchip, and Texas Instruments.

Silicon Image’s original PanelLink A/V scheme modulated audio data on the DVI clock; the competitive proposal instead broadcasts audio data on the existing serial-video data pins during horizontal and vertical blanking intervals, and Silicon Image has moved to a conceptually similar approach with HDMI. None of the approaches have yet secured DDWG formal approval, but Silicon Image is pushing forward with transmitter and receiver chips, and the company has cultivated working-group alliances with companies such as Hitachi, Matsushita/Panasonic, Philips, Sony, Thomson/RCA and Toshiba. The HDMI working group released its version 1.0 specification in early December.

With analog interconnect currently the plan of record, with music labels loath to support “in-the-clear” high-resolution digital audio interconnect, and with several copy-protected digital-interconnect proposals competing for your share of mind, why are companies, such as Cirrus Logic with its CS8406 and CS8416, introducing S/PDIF- and AES/EBU (European Broadcasting Union)-compatible, therefore copy-protection-lacking, digital audio transmitters and receivers? Part of the answer lies in the chips’ appropriateness in professional audio applications, such as recording gear, mixing boards, and editing workstations, for which copy protection is less of a concern. In the broader consumer-electronics arena, their inclusion is simply an insurance policy.

What does “insurance policy” mean? Well, what happens if consumers revolt against all of the copy-protection schemes being rolled out and drastically curtail their music purchases in protest? The record labels will be forced to backpedal, strip out watermarking and digital rights management, and find some other way of extricating cash out of folks’ wallets. Consumer-electronics manufacturers should therefore consider building in the ability to turn “on” unprotected high-resolution audio S/PDIF via a firmware upgrade, front-panel button sequence, or some other means, just in case copy protection fails—lest they face customer backlash of their own.k

Author Information

Technical editor Brian Dipert's auditory system may be unable to detect ultrasonic jams, but he's sure his four dogs and three cats have keen-enough hearing, and that they would want their tunes to be as high quality as possible. Do you think his pet-sensitive argument will secure spousal approval for the equipment he's always eyeing? Send other suggestions for how to persuade her to 1-916-454-5242, fax 1-916-454-5101, bdipert@edn.com.