It’s a trend happening everywhere today: devices are going wireless and connecting to the Internet. And not just the ubiquitous smartphones, tablets and the smart TV either; add to this a growing list of consumer electronics products: refrigerators, ovens, games consoles, central heating systems, weather stations, radios and home stereo systems.
Indeed the simple home stereo is struggling in the digital world. Countless inputs and control methods, incompatible interfaces, and way too many wires have created a home entertainment headache.
The dream of going wireless
Now that wireless connectivity is becoming more popular the next logical step is to incorporate wireless technology into the speakers themselves, creating an untethered audio experience to be enjoyed anywhere within the home. In turn these can build into fantastic multi-room systems enabling the music to follow the listener wherever they might be; unfortunately this is where many fall short.
Many high-end stereo systems offer “party mode” where several devices are linked together to play the same audio stream to create a multi-room experience. However sometimes the network is unreliable: perhaps the environmental conditions are unfavourable, or the location of the transmitter is unsuitable. Networked audio devices rely upon a master clock to keep them all synchronised; if that clock signal is lost or delayed due to poor bandwidth or intermittent network communications then “party mode” quickly becomes a jumbled cacophony of sound.
The problem of synchronicity and why synchronisation matters
One of the main difficulties in synchronising streams over TCP/IP networks is that they employ “best effort” methods to deliver IP packets: there’s no guarantee of delivery and packets arrive randomly, albeit within a reasonably predicable timeframe. Even using time-stamped multicast streams, clients will drift out of synchronisation and need to be periodically corrected. In the case of audio-visual stream delivery, the inherent latency within the network is often too large and unpredictable to reliably synchronise streams between more than a handful of client devices. Whilst it’s true that software time-stamping protocols running over TCP/IP provide some degree of synchronicity between pairs of devices, these methods have to factor in network latency, round-trip packet times plus have to account for buffering. This is sufficient for multi-room configurations but these methods are not fine-grained enough for channel-based audio, especially when maintaining separation between left and right stereo audio channels or recreating perfect 5.1 surround sound across wireless speakers.
Humans have evolved a highly accurate perception of sound spatial location, created by the brain analysing the minute variances in apparent amplitude and inter-aural time difference between sound sources. This occurs because the sound must travel slightly different distances to each ear. Studies have shown that fractions of milliseconds between sound waves arriving via left and right auditory pathways are sufficient for humans to accurately determine the direction of an audio source. In fact the human auditory system is so acutely sensitive that it is possible for us to distinguish sounds from two different locations where the angle between sources is as little as three degrees.
For products such as wireless speakers, therefore, a very tight synchronisation must be maintained between each in order to faithfully reproduce the spatial dynamics of the audio environment.
So how does Imagination’s Caskeid IP differ?
Whereas competitive solutions rely on proprietary technologies or software timing methods, Caskeid is unique in that it exploits timing signals intrinsic to the existing Wi-Fi infrastructure in order to guarantee devices are synchronised. The beauty of this approach means that Caskeid is immune from latency within the network; it also minimises clock drift, which would otherwise propagate across clients.
The figure above charts the deviation of a stereo (left-right) audio source between speakers over time, measured in milliseconds; zero deviation shows audio is perfectly synchronised, and any deviation (plus or minus) from the centreline means the stereo image is biased towards one of the two speakers, skewed either to the left or to the right.
The green line illustrates Caskeid’s performance in maintaining synchronisation between Wi-Fi connected stereo speakers. Caskeid is capable of guaranteeing a deviation of only 20µS between speakers with absolutely no drift and therefore no resultant shift in stereo image.
The figure below shows a comparison of the results obtained from Caskeid with three leading competitive technologies for wireless multi-room and stereo audio systems.
Competitor A illustrates the problems associated with poor synchronisation: the measured maximum deviation of 1.8mS (=1,800µS) coupled with the high rate of change between left and right channels means that accurate stereo reproduction is impossible. The listener will experience the sound field moving between speakers.
Competitor B’s solution attempts to maintain a constant synchronisation offset between speakers, which lessens the perception of the stereo image migrating across the sound stage. However during tests this technology needed an average of 25 minutes to converge in order to create a fully synchronised stereo pair. Contrast this with Caskeid’s ability to lock synchronisation between devices immediately and maintain synchronous operation indefinitely.
And finally, Competitor C provided the closest results to Caskeid. During our testing the technology exhibited a maximum 160µS deviation between speakers but required an average of 20 minutes to converge towards optimum synchronisation for stereo. Again compare this with Caskeid which, under identical conditions, is eight times more accurate in synchronisation from the outset.
Overall the competitive technology exhibits slow synchronisation, large drift between devices and therefore results in a shifting stereo image. Caskeid is proven to have class-leading performance with guaranteed microsecond accuracy of synchronisation across all wireless speakers to deliver an accurate and static stereo image, and faithful reproduction of the sound stage.
A real world implementation in Jongo wireless audio systems and Flow connected radios
It all sounds like good theory but how about a real world example? Fortunately Imagination doesn’t just license the IP; we also build products to prove the concepts and further refine the technology.
Imagination’s consumer electronics division, Pure, utilise Caskeid IP within their Jongo wireless speaker systems and Flow connected hybrid radios. All Jongo-enabled products are connected via Wi-Fi and Caskeid patented technology synchronises all radios and speakers connected via the access point.
Caskeid-enabled products are proven to yield microsecond precision between devices, capable of accurately reproducing left/right stereo channel separation and timing, or replicating surround sound systems wirelessly over standard IEEE 802.11n Wi-Fi. They achieve this because Imagination’s Ensigma communications IP uniquely maintains privileged access to the different network layers, affording the fine degree of control necessary to sustain synchronicity.
Add to this Imagination’s Flow technology for cloud-based services and device management and you have a fully featured, end-to-end solution for connected, synchronous and completely wireless audio.
Pure Connect: There’s an app for that!
As part of Caskeid Imagination also supplies the software framework and services necessary to build applications to control multi-room audio. Examples exist for both Android and iOS devices, using Imagination’s Flow APIs to access cloud-based music services and control wireless speakers and radios that form the multi-room audio solution.
The application provides a full Internet radio service, called FlowRadio, with instant access to over 20,000 stations worldwide, in addition to “listen again” services and approximately 270,000 podcast episodes online. To complement Internet radio, FlowMusic technology provides subscribers with a full streaming music service and offers the ability to purchase music tracks directly from any Flow-enabled audio device.
The entire package, including the APIs to interact with devices and the backend management tools, is available as a white-label service to our customers, providing a comprehensive suite of connected audio services with full back office support for account management, portal hosting and processing of online payments. Overall it’s a perfect complement to Caskeid-enabled connected audio products.
Want to know more? For further information on Caskeid, Flow and Ensigma IP, please go to our website at http://www.imgtec.com/ where you will be able to soon read the complete whitepaper.