High quality audio for low-power in-car portable applications
All this content is networked together and different people in the car can choose to listen to different audio sources, whether through the car's speakers or through headphones that enable individualized enjoyment of the various programs available.
Wireless audio has been around for some time. You can put on a headset without having to be physically tethered to the audio source. However, for portable applications, there has always been a challenge to find a solution that is both low power and can also transmit full CD-quality audio.
There are two options to transmit audio wirelessly: infrared and radio frequencies (RF). Infrared has heretofore been the most widely used due to low cost and high fidelity. However, is severely limited by line of sight issues since there can be no obstruction between the sender and the receiver. It is also susceptible to the heat of the sun on the dashboard. Any heat source can be a source of infrared interference. RF is more versatile. Some solutions operate on the FM band, but that limits their audio quality. Most higher quality solutions operate in what is called the Industrial, Scientific and Medical band (ISM band), because it is largely unregulated and doesn't require specific licensing. There are rules for how much power can be radiated, and the like, so there are some compliance requirements, but a provider does not need to apply for licenses to get spectrum allocated.
Technologies such as WiFi and Bluetooth operate in this band. They can also be used to transmit wireless audio, but there are some issues in terms of battery life and coexistence when there are several devices operating in close proximity.
Kleer technology, from SMSC, was developed with a goal to consume only small amounts of power to optimize portable, battery-powered operation, and to use a very narrow band in order not to interfere with or be affected by other devices in the ISM band. All this while transmitting full CD-quality lossless audio.
Kleer Technology provides one of the most power-efficient mechanisms to stream high-quality digital audio. A complete Kleer system only consumes about 30 mW of power, resulting in long battery life and the ability to use smaller power sources. This is also important even for line powered applications in today’s “green” world.
For example, there are untethered earbuds using Kleer technology that operate on very small 40 mAHr lithium ions coin cells for over 5 hours of playtime. Slightly larger 110 mAHr lithium polymers batteries are used in earbuds that play for 12 hours between charges; and 600 mAHr batteries are used in full-size headphones with extended range that can play music for 24 hours.
Other wireless technologies used for audio transmission often consume several multiples of the power that Kleer uses. For example, WiFi/WLAN radios typically consume on the order of 500-700 mW or more while they are transmitting. Bluetooth radios use on the order of 100-150 mW while streaming, and Bluetooth uses lossy compression so the signal is not even CD quality. Bluetooth 3.0 will offer more bandwidth, but it will use WiFi radios, further increasing power consumption. These solutions often require an extensive network management software stack running on external controllers, so the overall system ends up needing even more power. Kleer only needs a digital audio stream coming in at the source or going out to a D/A converter at the sink. Very simple devices are possible that require little more than the Kleer module.
Kleer technology transmits full 16 bit audio from a source to one or more sinks. The full bandwidth of the majority of today’s music content is available to be played back to the listener. The transmission is lossless and intelligent buffer management is used so interference from other radio frequency sources doesn’t interrupt the flow of sound. The result is sound that is as good at the remote receiver as it is at the source where it is being taken off a CD.
The figure below shows a test run by SMSC that compares the audio quality of Bluetooth (in red) and Kleer (in pink). There is about a 40 dB difference in the noise floor that can be attributed to the lossy compression used for Bluetooth audio.
In addition to superior audio quality, up to 4 sinks can be connected to each Kleer source so several people can listen to the same program. Bluetooth audio transmissions are essentially point-to-point, as typically only one sink is paired to one source for audio playback.
Coexisting in a Crowded World
Many wireless applications use the 2.4 GHz ISM band because. A few of the better known residents include WiFi/WLAN, microwaves, wireless phones, and Bluetooth, among many others.
The nature of the ISM band is such that devices often interfere with each other. A strong microwave signal can bring down a WiFi network or make it slow down to a crawl. Kleer technology has been specifically designed to both be less prone to interference from other devices and to be less susceptible to disturbances caused by other components that share the frequency spectrum in the ISM band.
In the case of WiFi, each channel takes up a 20-40 MHz spectral footprint.
Bluetooth uses twenty 1 MHz channels to transmit. It needs to hop over these channels, again taking up about 20 MHz of spectrum.
Kleer, on the other hand, uses a single 3 Mhz channel that can be placed adjacent to the WiFi channels.
This small spectral footprint enables Kleer to be more resistant to interference from other sources while at the same time producing little interference itself, so as not to disrupt other services.
Kleer products are designed to operate with each other. Any Kleer audio source on the market today can play over any other Kleer headphone or speaker.
Interoperability is an important feature as consumers can use their favorite headset with whatever Kleer source they come in contact with, whether their own or one that belongs to someone else.
Kleer in the Automobile
For the car, cutting loose from wires brings freedom, control and increased safety. Kleer technology makes long and potentially dangerous wires from headphone jacks to the headphones obsolete. The risk of getting entangled in these wires, particularly for children, is eliminated. In emergency situations, this may save important time.
For pure listening pleasure, the freedom to conveniently choose multimedia content and to quickly adjust audio parameters is crucial. Although car designers try to arrange controls for rear seat entertainment systems in ergonomically favorable positions, wireless remote controls have advantages over fixed panels. Kleer technology uses RF signals and can transmit data beyond just digital audio streams. The same technology that brings excellent sound to the passengers in the car also allows building remote controls which do not use infrared technology that can be blinded by sunlight, or needs aiming at IR receivers. Kleer technology is able to transport data and control signals in parallel with high-quality digital audio streams.
Kleer technology is a wireless audio technology optimized for low–power, portable applications. It transmits full CD-quality audio over the ISM band, without loss of fidelity. It has been designed to offer good coexistence with other technologies that use the same RF band. In addition, Kleer products interoperate with each other to provide flexibility to the consumer.
About the Author:
Henry Muyshondt is Senior Director of Business Development at SMSC. Mr. Muyshondt holds a Bachelor of Science in Electrical Engineering from the University of Florida as well as a Masters of Business Administration from the University of North Carolina at Charlotte. He holds 9 US patents.
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