Introduction In an increasingly wireless world, home audio is one of the last holdouts for physical cabling. A typical home theater system may require as many as eight speaker cables, each of which has to be run somehow from the source to the speaker. The practical advantages of replacing the copper rat’s nest with a wireless solution should be obvious to anyone who has ever had to pull speaker cable through an attic, under a floor or through walls. However, up until now, wireless home audio has not delivered the HD audio quality consumers demand. This is about to change. The WiSA™ (Wireless Speaker and Audio) Association, established in 2011, fosters a new quality and interoperability standard for the wireless transmission of HD audio in a home entertainment environment. Created by a group comprised of industry leaders from across the home theater ecosystem, the association’s main charter is to certify interoperability between WiSA-compliant transmitters, such as DTVs, set top boxes, and Blu-ray players, with receivers, comprising home theater speakers from many brands. WiSA compliance starts with a common wireless speaker technology that provides high-reliability, highfidelity surround audio via the U-NII frequency spectrum for an interference-free HD audio experience of exceptional quality. To ensure that every consumer gets an easy-to-use, high quality experience in their system regardless of their purchasing decision, WiSA testing makes sure that every conforming piece of equipment, regardless of brand, interoperates without degrading the quality promised by the underlying technology. These are the subjects of this white paper. The WiSA logo on equipment stands for great audio quality, high reliability, ease of setup, scalability, and global interoperability with no compromises.
WiSA System Standards With speaker cables, consumers have simple and realistic expectations. They expect the sound to come out of the speaker with the best quality afforded by the content and the investment in their equipment. Once connected correctly, speaker cables only cause sound interruptions or noise when they have worn out – and certainly only once in a lifetime. Except in extreme circumstances, a speaker cable can connect equipment from any brand to speakers from any number of brands. Brands can even be mixed and matched. Speaker cable problems can be diagnosed just by looking at them. Wire is conceptually simple. Introducing wireless connectivity necessarily introduces complexity. Quality now relates to abstract concepts such as bandwidth, sample rate, and format – terms previously reserved for media distribution. Reliability depends on ethereal radio concepts – power, frequency bands, interference, and error Whitepaper
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handling. Adding new speakers involves networking concepts such as discovery, addressing, and protocol. These concepts must all be brought in line with what consumers expect in order to gain adoption for the wireless approach.
No Wires! Transmitter
On the other hand, wires cause a major inconvenience. With wires, the user has to dig around behind equipment, try to get the wires into those clips or binding posts without falling out, place the wires into the correct channels, and set the correct phases. Furthermore, the speaker wires must be routed to the speakers. Many times, consumers run the wires across the floor, under rugs, or over doorways. Those with more money or energy work the wires through the walls, in ceilings, or under floors. Once the wires are run, the possible speaker locations dictated by wire placement become a significant factor in placing and rearranging furniture.
Speaker Receivers With wireless, all of the disadvantages of wires disappear. The speakers need only be placed in the room, with each one approximately in the right place. The speakers assign themselves to the correct channel. Phase is correct from the factory. When it is time to rearrange the room, the speakers can simply be moved with the furniture. To summarize, consumers demand that wireless audio must sound great, perform without pops, clicks, hiss or other distracting artifacts, scale to larger (or smaller) systems, and be interoperable across brands. As a bonus, wireless is easy to set up and reconfigure.
Great Sound The quality of speaker wire is a matter of diameter based on the power to be delivered over a given length. Salespeople are generally well trained in helping consumers with this choice. Even if these parameters aren’t quite met, the resulting sound will have decent fidelity. Analog wireless is plagued by serious hiss, hum, and squelching artifacts, and has only succeeded in high-end professional systems. Good wireless speakers systems were only a dream at that point. Digital systems are able to perform exact error correction for small problems, and with larger problems, can conceal them so well that it’s very hard if not impossible to notice. All new wireless audio systems are digital. Now that the digital decision is made, how the digital data will be used becomes an issue that depends on power, bandwidth, cost, and complexity. The digital wireless game starts with frequency bands, each of which has legislated power and bandwidth limits. Furthermore, those bands are generally shared with other traffic (as is the case with WiFi and Bluetooth bands), further restricting bandwidth availability. There is little room left for audio data. To ensure some level of robustness, digital wireless audio systems compromise by reducing the sample rate or performing compression, both of which reduce quality. Whitepaper
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Reducing the sample rate rolls off high frequencies, making the content sound muffled. Compression effects the sound two ways: it introduces artifacts such as hissing or ticking and it introduces latency. The better the compression the more complex it becomes. With increased complexity comes increased computation (cost) to compress and decompress the signal. This induces latency in the system that can cause lip sync problems or frustrate game players. Furthermore, if the latency is variable, then related content playing to multiple speakers could arrive at a different time, ruining the surround experience. To be sure, audio has different requirements than information networks because of its persistent desire for constant delivery. Information networks are generally built for the highest possible bandwidth, but not for constant delivery. Maximum bandwidth is achieved by allowing a content stream to proceed with minimum interruptions for however long it takes. One of these long bursts could continue for many milliseconds, causing interruptions in audio data. To cover up these interruptions, audio is delivered in similar long bursts, but large bursts take a long time to play. The amount of latency introduced depends on how long the audio must wait for its turn. To succeed, wireless sound quality should match the content for best reproduction regardless of media, and this is where WiSA compliance draws a line:
24-bit uncompressed audio – HD Audio quality, perceptibly 50% better than CDs Sample rate that matches the content: 32, 44.1, 48, and 96k samples/sec – Realistic sound, 2 times better than CDs, HD Audio quality Rapid error detection and recovery – smooth, uninterrupted sound 5 ms fixed latency – perfect lip synch and game response Under 160ns speaker-to-speaker delay – theatre quality surround experience Amplifiers and speakers matched and balanced as a unit – same quality sound in all directions
Relative Quality High-quality Stereo MP3 Stereo CD Audio (> 6x)
Stereo HD Audio (> 18x)
WiSA compliance ensures great sound for home theater and live performance.
An interesting note is that wireless increases fidelity over wired speakers because a wireless speaker must have an integrated amplifier. This means that the wireless amplifier and speaker drivers are matched, equalized, and phase-matched by design. With wired speakers, the (pre)amplifier must compensate for speaker power and frequency response. This also means that less expensive wireless speakers can have better quality than even superior wired speakers. That a WiSA-compliant system operates with such high quality makes no difference to how content is used. Uncompressed audio is a universal format that is independent of the kind of music played. Network audio, MP3, Dolby Digital™, DTS™, CDs and other formats are played through a WiSA-compliant system with the best possible fidelity. In fact, uncompressed audio is future-proof because new audio coding approaches can always be converted seamlessly to the uncompressed format with true fidelity.
Robust Performance Wired speakers are completely robust; however, wireless audio systems must take special care to meet this important customer challenge. Wireless has the reputation for adding annoying artifacts such as Whitepaper
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drops, pops, clicks, hisses, and the like. To reverse this trend, WiSA compliance ensures that these artifacts are eliminated. When it comes to improving wireless quality, the best defense is a good offence. WiSA audio avoids the popular digital audio frequencies used by WiFi, Bluetooth, baby monitors, and microwave ovens. A set of frequencies have been opened up within the international unlicensed (U-NII) 5 GHz radio band that require Dynamic Frequency Selection (DFS) procedures. These frequencies were historically reserved for weather and military radar applications, but have recently become available as long as conflicts with these important functions are avoided. A WiSA compliant transmitter goes one step further and does its best to find a totally unoccupied channel. Further, it also looks ahead for another unoccupied channel, so in case of interference, it can jump directly to that channel without losing a single bit of audio information.
The UNII Band
The DFS channels from 52-140 go mostly unused, leaving plenty of quality space for wireless audio shown on DFS channel 56. 5GHz 802.11nWiFi traffic is shown on channels 40-48 and 153-161. The transmitter is looking ahead to find the next DFS channel for it to occupy. Because the nature of 5 GHz radio and strict DFS requirements, DFS frequencies are seldom used, and the U-NII band has up to 24 available channels, leaving plenty of room for all of the neighbors. By working in a clean radio band and using it to its fullest, almost all of the reliability problems with wireless communications are avoided. As a bonus, WiSA-compliant audio will not interfere with existing networks – no degradation of WiFi performance is experienced.
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Because of wide available bandwidth and fewer errors due to interference, low-latency and economical approaches to quality can be exercised. In case of inevitable communication errors, the system falls back on tried-and-true recovery methods, such as those used on CDs:
Forward error correction – extra data is sent to make 100% repairs Error concealment – missing (uncorrected) data is filled in a way that is unnoticeable. Play-out buffer – allows longer concealment ability Silence – avoid noisy artifacts at all cost
All WiSA compliant components are all tested in to ensure clean communications within a 30x30 foot (10x10m) area even when interference is present. Frequency selection and correction must operate quickly and free of noise.
Easy Setup and Optimization WiSA compliant ensures that components are simply easy to set-up. Just position the speakers conveniently in the room, then plug-in the transmitter unit (TV, disc player, game console, AV Receiver) and the speakers into mains power. If the speaker positions need to change, then they can simply be moved. There are no speaker cables, connection, or speaker-amplifier matching to do. Channels (e.g. Front, surround, rear, right, left, center) are assigned to speakers either automatically or by selection on a screen. This is the same for letting the system know the locations of the speakers. In less expensive systems, selection is done visually by using an on-screen display (OSD) or using a mobile app as shown below: The speakers are simply dragged to the correct relative positions in the room to assign channels and determine the distance between speakers. From there, the components correct for volume and the delay in the room. The listener position can even be changed by dragging (e.g. from the left to right side of the couch) and the system instantly adapts by again changing the volume and delay for all of the speakers.
For more fully-featured speakers, the automatic approach involves the use of ultrasonic transducers (“pingers”), for which WiSA compliance has a provision for correct interoperability over the entire room size. Each speaker contains a pinger and from one speaker, the distances are measured to all of the other speakers, much like the way whales, dolphins, and bats locate things. This serves the purpose of automatically mapping the locations of the speakers and their channel assignments just by turning on the system.
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Note that the transmitter never contains a pinger and can support both manual and automatic approaches, making WiSA compliant transmitters universal and low-cost. Listener location can still be changed manually, and the OSD or app shows the automatically derived positions from the pingers. With the addition of another pinger to a WiSA compliant remote control, the listener position is determined automatically with the touch of a button.
Scalability WiSA compliance ensures interoperability among transmitter and speaker brands. This is particularly important when it comes to scaling. When a customer buys their initial system, they may simply get a sound bar and possibly a subwoofer bundled with a TV. Later on, as they get comfortable with their home theatre setup and want more capability, they buy a set of surround speakers. They may move the system to another room or house, and can use
front speakers. They then realize that they have access to 6.1 or 7.1 titles and want to take maximum advantage and buy rear speakers and possibly a WiSA compliant AV receiver with a 7.1 decoder. A child could move out of the house and the basic system given to them, replaced with higher quality components for the now-missing pieces. Consumers’ decisions might be made due to features, quality, cost, or even color. The important point is that they have choices as they expand their system and are not limited to the decisions made by a single brand. To achieve this, the WiSA certification and testing programs ensures that all brands interact correctly. Whitepaper
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Global Interoperation The WiSA Association’s mission is to ensure that the consumer gets the best possible experience from their wireless speaker system purchases. This means that the consumer can have choices, return and improve their system, have a great out-of-the-box experience, and be comforted that their decision to go wireless was a good one. To do this, the WiSA Association produces a Certification and Test Suite (CTS) to which all equipment that bears the WiSA logo complies. The CTS specifically tests interoperation of all of the features described above for both transmitters and receivers. Simplay® Labs, LLC (the same experienced company that tests HDMI compliance) has been selected to provide WiSA compliance testing world-wide. As part of testing, they will also test equipment for compatibility to other equipment already on the market. To help vendors (ODMs, OEMs, and brands) develop products that can pass the CTS, the WiSA Association also provides not only the CTS to its members, but also white papers, application notes, and reference designs. The CTS environment can be reproduced in-house to ensure best success for final testing.
Conclusion WiSA compliance offers a compelling value proposition in home audio, home theater, and DTV applications centered on the consumer experience. It ensures that wireless audio offers performance and reliability on a par with legacy wired connections. From a usability standpoint, it allows for simple system set-up and configuration, eliminating a significant barrier to home theater adoption and making 5.1 and 7.1 surround audio easy for consumers to adopt. Most importantly, when the consumer sees the WiSA Logo, they are ensured that their wireless speakers are as universal as connecting speakers with speaker wire. Any choice of source equipment – either type or brand – can be mixed and matched with speakers from any brand. This is done without compromising, rather improving upon the wired speaker experience. For more information, please visit www.wisaassociation.org
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© 2011 WiSA, LLC. All rights reserved. Descriptions and specifications contained in this document are subject to change without notice and may differ from country to country. WiSA and the WiSA logo are a trademark, registered trademark or service mark of WiSA, LLC in the United States and/or other countries. All other trademarks and registered trademarks are the property of their respective owners in the United States and/or other countries. Product specifications are subject to change without notice. 12/2011. Whitepaper
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