Mechanics Hate Us

Multi-channel audio has become mainstream and manufacturers have come up with many types of basic and more advanced technologies like wireless surround speakers, virtual surround sound to simplify the installation of home theater products. I will review the latest trends to understand which devices really work. I will also give some guidance for choosing the best components.

Historically, setting up a TV would be speedy since they would already provide built-in stereo speakers. This, though, has all changed with multi-channel sound. These days external speakers are used to create a surround sound effect. The most commonly used 5.1 surround sound format requires installing a total of 6 loudspeakers. These are one center speaker, two front side speakers, two rear speakers and a subwoofer. The more recent 7.1 standard increases this number to 8 by adding two extra side speakers.

As a result, home theater setups have turn out to be fairly complicated. Running cables to remote loudspeakers also is often undesirable because of aesthetic reasons. A number of technologies have emerged to simplify this procedure.

The first approach is building so-called virtual speakers by applying signal-processing to the audio and introducing phase shifts and special cues to those audio components that would ordinarily be broadcast by the remote loudspeakers. The signal processing is engineered based on how the human hearing determines the location of a sound. The audio signal is then broadcast by the front loudspeakers. Due to the signal processing, the viewer is deceived into thinking the sound is originating from virtual remote surround speakers.

Virtual surround eliminates the remote speakers and simplifies the setup and also avoids long speaker cord runs. On the other hand, it also has a drawback. The form of each human’s ear is slightly dissimilar. For that reason everybody processes sound in a different way. The signal processing is based on measurements which are done using a standard human ear model. If the shape of the ear changes, sound will travel differently. For that reason virtual surround will not function equally well for every person.

One more method for simplifying home theater setups and avoiding long speaker cord runs is to employ wireless surround sound devices or wireless speakers. A wireless solution will normally incorporate a transmitter module that connects to the TV or source and wireless amplifiers that will be connected to the remote loudspeakers. The transmitter will normally have amplified speaker inputs as well as line-level inputs and come with a volume control to adjust it to the source audio level.

Some wireless speaker products are designed to connect 2 loudspeakers per wireless amplifier. A better solution would provide a wireless amplifier for each remote speaker to avoid the cord runs between each of the 2 remote loudspeakers. The most basic wireless systems utilize FM transmission. FM transmission is susceptible to noise and audio distortion. More sophisticated devices make use of digital audio transmission to completely preserve the original audio. To make certain that all speakers are in sync in a multi-channel application, make certain that you pick a wireless system that has an audio latency of just a few milliseconds at most. If the latency is higher than 10 ms then there will be an echo effect which will deteriorate the surround sound. Wireless kits frequently use the 900 MHz or 2.4 GHz frequency band. Some products also use the 5.8 GHz band. These products have less competition from other wireless gadgets than products utilizing the crowded 900 MHz or 2.4 GHz bands.

Another solution are side-reflecting speakers. These kits are also known as sound bars. There are additional loudspeakers positioned at the front which broadcast the sound for the remote loudspeakers from the front at an angle. The audio is then reflected by walls and seems to be coming from besides or behind the viewer. The effect by and large depends on the shape of the room and interior design and not work well in a lot of real-world scenarios due to different room shapes and obstacles in the room.

Latest wireless audio gadgets such as iPods, wireless headphones and cell phones support latest wireless protocols. These protocols are supposed to cut the cord and deliver perfect high-fidelity audio. We will look at some of the newest devices to discover which applications they work for.

These devices fall into 2 categories. The first category of products already has wireless built in. Second-category products, including a few streaming audio products, have optional wireless capability. Normally they have a slot to add a wireless LAN card. Latest generation iPods and cell phones already come with built-in WiFi and Bluetooth support.

The Bluetooth protocol is a relatively low-cost solution. Yet, its limitations have an influence on high-quality audio applications and are often overlooked.

1) Inadequate operating range

Bluetooth devices typically merely have a 30-foot range which confines Bluetooth to single-room applications.

2) Audio compression because of restricted data rate

Bluetooth offers a maximum reliable data rate of roughly 1 Mbps only. This rate is not large enough to send uncompressed CD-quality audio. Consequently Bluetooth wireless devices use audio compression. This is less critical though for compressed audio such as MP3 audio but excludes Bluetooth from use in high-quality audio applications.

3) Signal latency

As a consequence of audio compression, Bluetooth will introduce a signal delay of no less than 10 ms which will cause the audio to be somewhat out of sync in case of video and real-time applications. This is again less of a dilemma for MP3 players.

4) No multiple headphone support

Bluetooth cannot stream to numerous headphones at the same time. This may be a problem in cases where a number of people like to listen to the same Bluetooth transmitter.

Uncompressed audio streaming is supported by WiFi. WiFi is a very common protocol. Yet, WiFi also has limitations in regard to simultaneous transmission to a number of receivers. Because of the fairly high power consumption it is rarely used in wireless headphones though. WiFi is suitable for streaming audio from a PC however because nearly all PCs have WiFi access.

Wireless speakers and wireless amplifier products for home theater speakers typically utilize their own proprietary protocol. Entry-level wireless headphones and speakers generally still utilize FM transmission which offers low cost but is prone to noise and audio degradation.

More recent wireless audio protocols are based on digital transmission. This avoids audio degradation. A number of protocols also incorporate error correction to cope with interference from other wireless products.

Newest-generation wireless amplifiers permit streaming to an infinite number of receivers and support uncompressed audio transmission.

The audio latency ranges from below 1 ms to up to 20 ms. A small latency is vital for wireless surround sound applications. These wireless audio transmitters typically work at 2.4 GHz. There are also some devices such as Amphony’s line of wireless audio devices which work at 5.8 GHz. Products that work at 5.8 GHz have less competition from other wireless devices than those using the crowded 2.4 GHz frequency band.

Wireless amplifiers are available with different levels of audio quality, power consumption and standby power. Getting a high-quality low-distortion amplifier is vital for good sound quality. Wireless Class-D amplifiers typically have standby power of 5 Watts or less and a power efficiency of larger than 80% but sometimes high audio distortion. It is vital to select a wireless amplifier with low audio distortion. This will guarantee good sound quality. High-quality amplifiers have audio distortion of 0.05% or less.

Multi-channel audio has become mainstream and manufacturers have come up with many types of basic and more advanced technologies like wireless surround speakers, virtual surround sound to simplify the installation of home theater products. I will review the latest trends to understand which devices really work. I will also give some guidance for choosing the best components.

Historically, setting up a TV would be speedy since they would already provide built-in stereo speakers. This, though, has all changed with multi-channel sound. These days external speakers are used to create a surround sound effect. The most commonly used 5.1 surround sound format requires installing a total of 6 loudspeakers. These are one center speaker, two front side speakers, two rear speakers and a subwoofer. The more recent 7.1 standard increases this number to 8 by adding two extra side speakers.

As a result, home theater setups have turn out to be fairly complicated. Running cables to remote loudspeakers also is often undesirable because of aesthetic reasons. A number of technologies have emerged to simplify this procedure.

The first approach is building so-called virtual speakers by applying signal-processing to the audio and introducing phase shifts and special cues to those audio components that would ordinarily be broadcast by the remote loudspeakers. The signal processing is engineered based on how the human hearing determines the location of a sound. The audio signal is then broadcast by the front loudspeakers. Due to the signal processing, the viewer is deceived into thinking the sound is originating from virtual remote surround speakers.

Virtual surround eliminates the remote speakers and simplifies the setup and also avoids long speaker cord runs. On the other hand, it also has a drawback. The form of each human’s ear is slightly dissimilar. For that reason everybody processes sound in a different way. The signal processing is based on measurements which are done using a standard human ear model. If the shape of the ear changes, sound will travel differently. For that reason virtual surround will not function equally well for every person.

One more method for simplifying home theater setups and avoiding long speaker cord runs is to employ wireless surround sound devices or wireless speakers. A wireless solution will normally incorporate a transmitter module that connects to the TV or source and wireless amplifiers that will be connected to the remote loudspeakers. The transmitter will normally have amplified speaker inputs as well as line-level inputs and come with a volume control to adjust it to the source audio level.

Some wireless speaker products are designed to connect 2 loudspeakers per wireless amplifier. A better solution would provide a wireless amplifier for each remote speaker to avoid the cord runs between each of the 2 remote loudspeakers. The most basic wireless systems utilize FM transmission. FM transmission is susceptible to noise and audio distortion. More sophisticated devices make use of digital audio transmission to completely preserve the original audio. To make certain that all speakers are in sync in a multi-channel application, make certain that you pick a wireless system that has an audio latency of just a few milliseconds at most. If the latency is higher than 10 ms then there will be an echo effect which will deteriorate the surround sound. Wireless kits frequently use the 900 MHz or 2.4 GHz frequency band. Some products also use the 5.8 GHz band. These products have less competition from other wireless gadgets than products utilizing the crowded 900 MHz or 2.4 GHz bands.

Another solution are side-reflecting speakers. These kits are also known as sound bars. There are additional loudspeakers positioned at the front which broadcast the sound for the remote loudspeakers from the front at an angle. The audio is then reflected by walls and seems to be coming from besides or behind the viewer. The effect by and large depends on the shape of the room and interior design and not work well in a lot of real-world scenarios due to different room shapes and obstacles in the room.

Latest wireless audio gadgets such as iPods, wireless headphones and cell phones support latest wireless protocols. These protocols are supposed to cut the cord and deliver perfect high-fidelity audio. We will look at some of the newest devices to discover which applications they work for.

These devices fall into 2 categories. The first category of products already has wireless built in. Second-category products, including a few streaming audio products, have optional wireless capability. Normally they have a slot to add a wireless LAN card. Latest generation iPods and cell phones already come with built-in WiFi and Bluetooth support.

The Bluetooth protocol is a relatively low-cost solution. Yet, its limitations have an influence on high-quality audio applications and are often overlooked.

1) Inadequate operating range

Bluetooth devices typically merely have a 30-foot range which confines Bluetooth to single-room applications.

2) Audio compression because of restricted data rate

Bluetooth offers a maximum reliable data rate of roughly 1 Mbps only. This rate is not large enough to send uncompressed CD-quality audio. Consequently Bluetooth wireless devices use audio compression. This is less critical though for compressed audio such as MP3 audio but excludes Bluetooth from use in high-quality audio applications.

3) Signal latency

As a consequence of audio compression, Bluetooth will introduce a signal delay of no less than 10 ms which will cause the audio to be somewhat out of sync in case of video and real-time applications. This is again less of a dilemma for MP3 players.

4) No multiple headphone support

Bluetooth cannot stream to numerous headphones at the same time. This may be a problem in cases where a number of people like to listen to the same Bluetooth transmitter.

Uncompressed audio streaming is supported by WiFi. WiFi is a very common protocol. Yet, WiFi also has limitations in regard to simultaneous transmission to a number of receivers. Because of the fairly high power consumption it is rarely used in wireless headphones though. WiFi is suitable for streaming audio from a PC however because nearly all PCs have WiFi access.

Wireless speakers and wireless amplifier products for home theater speakers typically utilize their own proprietary protocol. Entry-level wireless headphones and speakers generally still utilize FM transmission which offers low cost but is prone to noise and audio degradation.

More recent wireless audio protocols are based on digital transmission. This avoids audio degradation. A number of protocols also incorporate error correction to cope with interference from other wireless products.

Newest-generation wireless amplifiers permit streaming to an infinite number of receivers and support uncompressed audio transmission.

The audio latency ranges from below 1 ms to up to 20 ms. A small latency is vital for wireless surround sound applications. These wireless audio transmitters typically work at 2.4 GHz. There are also some devices such as Amphony’s line of wireless audio devices which work at 5.8 GHz. Products that work at 5.8 GHz have less competition from other wireless devices than those using the crowded 2.4 GHz frequency band.

Wireless amplifiers are available with different levels of audio quality, power consumption and standby power. Getting a high-quality low-distortion amplifier is vital for good sound quality. Wireless Class-D amplifiers typically have standby power of 5 Watts or less and a power efficiency of larger than 80% but sometimes high audio distortion. It is vital to select a wireless amplifier with low audio distortion. This will guarantee good sound quality. High-quality amplifiers have audio distortion of 0.05% or less.

Avoiding the big clutter of cables has lead to a multitude of wireless audio transmitter products over the years which claim to untie your home audio equipment. Can these devices make good on their promise to eliminate the cable clutter? What influence has changing technology had on their performance?

Wireless transmission of music has started with the launch of commercial radio broadcasts several decades ago. While still being popular today, FM radio is now being substituted by new technologies such as HD radio, satellite radio and DAB broadcasts. Today a variety of consumer devices exist such as wireless microphones, wireless surround sound kits, Bluetooth audio transmitters, baby monitors etc which cut the cord by transmitting audio wirelessly.

Many homes which are not wired for audio are perfect for using wireless audio to distribute music all through the home. The technologies used today all have pros and cons as we will examine.

One of the most traditional technologies is FM broadcasting. Audio is sent via a radio-frequency signal which is modulated (changed in frequency) with an audio signal. The technology, which is known as frequency modulation (FM), is fairly straightforward and cost-effective to build and offers high range. Most of today’s wireless consumer products utilize FM transmission. FM, however, has serious drawbacks compared with newer technologies.

The first problem is the fact that the broadcast will pick up noise and thus there will be some hiss or static. The amount of noise will in fact vary based on the location of the radio or receiver. This is due to the fact that the radio signal is bouncing off walls and will cancel itself out at different locations. This phenomenon is called multi-path fading. Using two antennae is one approach some devices utilize to cope with this difficulty (diversity receivers). Another difficulty is that FM radios easily pick up interference from competing wireless transmitters.

Bluetooth has gained popularity lately for wireless audio transmission even though this protocol was primarily designed to connect computer peripherals. Before the signal is sent, Bluetooth transmitters will convert the audio into a digital format. While offering high robustness against wireless interference, Bluetooth has several problems in regard to audio transmission since it was never designed with the purpose of transmitting audio. The range of the transmission is only 30 ft or less. Moreover, Bluetooth does not have enough space to transmit an uncompressed CD-quality audio signal. Consequently the audio is compressed prior to the transmission. Due to the compression, the audio quality will be degraded compared to the original. The final drawback is the fact that Bluetooth will cause a delay in the signal (also called latency) which is a problem when used together with video because the audio will be out of sync or if used in a surround sound setup where some of the loudspeakers would be out of sync with the hard-wired speakers.

Terrestrial digital and satellite radio technologies offer high range but use extensive audio compression and have an audio delay of up to several seconds.

The technology used in Amphony’s wireless audio transmitters sends audio in a digital format without audio compression. The audio signal will keep CD quality because no audio compression is used. The audio latency of these products is less than 1 ms and as a result this technology is also used in wireless speaker kits for home theater setups.

This technology is fairly robust against radio interference from other wireless transmitters by employing a method called forward error correction. Rather than using the crowded 900 MHz and 2.4 GHz frequency bands, Amphony products operate at 5.8 GHz and thus offer high robustness. An advantage over Bluetooth is the ability to send audio to any number of wireless receivers from a single transmitter. This is important for distributing audio to several rooms in the residence.