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The fundamental principle of bass management (also called LFE crossover) in surround sound replay systems is that bass content in the incoming signal, irrespective of channel, should be directed only to loudspeakers capable of reproducing it, whether the latter are the main system loudspeakers or one or more subwoofers. [1]
There are notation differences between the pre-bass-managed signal and after it has passed through the bass manager. For example, when using 5.1 surround sound:[ original research? ]
| Original | Managed |
|---|---|
| FL – Front left | FL – Front left |
| FR – Front right | FR – Front right |
| C – Center | C – Center |
| SL – Surround left | SL – Surround left |
| SR – Surround right | SR – Surround right |
| AW – Alternative woofer | N/A (incorporated into SW) |
| N/A (bass can be in any channel) | SW – Subwoofer |
As the table shows, the bass manager directs bass frequencies from all channels to one or more subwoofers, not just the content of the low-frequency effects (LFE) channel. However, when there is no subwoofer, the bass manager directs the LFE channel to the main speakers. This is the only time the LFE channel would not be sent to the subwoofer. The key concept is that the LFE channel is not the subwoofer channel. [2]
A typical configuration of a bass-managed 5.1-channel surround-sound loudspeaker system is shown in the first diagram. [3] [4]
As shown in the bass management block diagram, a 5.1-channel audio system consists of five discrete, full-range main channels (front left, center, front right, surround left, and surround right), plus a band-limited low-frequency effects (LFE) channel for added bass (this corresponds to the .1). In such a system, the use of bass management allows the redirection of low-frequency signals from any of the five main speakers to the subwoofer (SW).
The high-pass filters applied to each of the main channels are typically 12 dB/octave and use a Butterworth filter. These are complemented by a 24 dB/octave low-pass filter in the subwoofer feed, which typically uses a Linkwitz-Riley filter topology. This approach takes into account the natural low-frequency responses of the main speakers, which roll off at 12 dB/octave for sealed enclosures, and 18–24 dB/octave for vented enclosures. The aim is to have the low-pass filtered and high-pass filtered signals be −6 dB at the crossover frequency, producing what is known as an acoustical 4th-order Linkwitz-Riley alignment of reasonable accuracy. This helps to ensure that the low-frequency response of each of the main channels is extended downwards with a flat acoustical response.[ original research? ] In the diagram, a 60 Hz crossover frequency has been illustrated, but this can typically vary between 40 and 80 Hz.
The LFE channel is a separate channel that contains low frequencies only, and it was originally added to magnetic 70mm-movie soundtracks in the 1970s, to be reproduced through subwoofers. [3] It is designed to be amplified by 10 dB on playback and summed into the signal going to the subwoofer. The LFE channel for movies has a frequency range extending to 120 Hz, and some AV receivers apply a 120-Hz low-pass filter during playback, and this frequency is independent of the settings of the low-pass and high-pass filters that are applied to the main speakers. As some less expensive AV receivers offer only a fixed bass-management crossover frequency (often at 80 Hz) using one filter, Dolby 5.1-channel music mixing guidelines recommend that the LFE channel be rolled off at 80 Hz, otherwise frequency content between 80 Hz and 120 Hz could be lost. [3]
A subwoofer is a loudspeaker designed to reproduce low-pitched audio frequencies known as bass and sub-bass, lower in frequency than those which can be (optimally) generated by a woofer. The typical frequency range for a subwoofer is about 20–200 Hz for consumer products, below 100 Hz for professional live sound, and below 80 Hz in THX-certified systems. Thus one or more subwoofers are important for high quality sound reproduction as they are responsible for the lowest two to three octaves of the ten that are audible. This very low-frequency (VLF) range reproduces the natural fundamental tones of the bass drum, electric bass, double bass, grand piano, contrabassoon, tuba, in addition to thunder, gunshots, explosions, etc.
A loudspeaker is an electroacoustic transducer that converts an electrical audio signal into a corresponding sound. A speaker system, also often simply referred to as a speaker or loudspeaker, comprises one or more such speaker drivers, an enclosure, and electrical connections possibly including a crossover network. The speaker driver can be viewed as a linear motor attached to a diaphragm which couples that motor's movement to motion of air, that is, sound. An audio signal, typically from a microphone, recording, or radio broadcast, is amplified electronically to a power level capable of driving that motor in order to reproduce the sound corresponding to the original unamplified electronic signal. This is thus the opposite function to the microphone; indeed the dynamic speaker driver, by far the most common type, is a linear motor in the same basic configuration as the dynamic microphone which uses such a motor in reverse, as a generator.
A Dolby noise-reduction system, or Dolby NR, is one of a series of noise reduction systems developed by Dolby Laboratories for use in analog audio tape recording. The first was Dolby A, a professional broadband noise reduction system for recording studios in 1965, but the best-known is Dolby B, a sliding band system for the consumer market, which helped make high fidelity practical on cassette tapes, which used a relatively noisy tape size and speed. It is common on high-fidelity stereo tape players and recorders to the present day, although Dolby has as of 2016 ceased licensing the technology for new cassette decks. Of the noise reduction systems, Dolby A and Dolby SR were developed for professional use. Dolby B, C, and S were designed for the consumer market. Aside from Dolby HX, all the Dolby variants work by companding: compressing the dynamic range of the sound during recording, and expanding it during playback.
Audio crossovers are a type of electronic filter circuitry that splits an audio signal into two or more frequency ranges, so that the signals can be sent to loudspeaker drivers that are designed to operate within different frequency ranges. The crossover filters can be either active or passive. They are often described as two-way or three-way, which indicate, respectively, that the crossover splits a given signal into two frequency ranges or three frequency ranges. Crossovers are used in loudspeaker cabinets, power amplifiers in consumer electronics and pro audio and musical instrument amplifier products. For the latter two markets, crossovers are used in bass amplifiers, keyboard amplifiers, bass and keyboard speaker enclosures and sound reinforcement system equipment.
A woofer or bass speaker is a technical term for a loudspeaker driver designed to produce low frequency sounds, typically from 20 Hz up to 80 Hz. The name is from the onomatopoeic English word for a dog's bark, "woof". The most common design for a woofer is the electrodynamic driver, which typically uses a stiff paper cone, driven by a voice coil surrounded by a magnetic field.
Surround sound is a technique for enriching the fidelity and depth of sound reproduction by using multiple audio channels from speakers that surround the listener. Its first application was in movie theaters. Prior to surround sound, theater sound systems commonly had three screen channels of sound that played from three loudspeakers located in front of the audience. Surround sound adds one or more channels from loudspeakers to the side or behind the listener that are able to create the sensation of sound coming from any horizontal direction around the listener.
The low-frequency effects (LFE) channel is a band-limited audio track that is used for reproducing deep and intense low-frequency sounds in the 3–120 Hz frequency range.
Audio system measurements are a means of quantifying system performance. These measurements are made for several purposes. Designers take measurements so that they can specify the performance of a piece of equipment. Maintenance engineers make them to ensure equipment is still working to specification, or to ensure that the cumulative defects of an audio path are within limits considered acceptable. Audio system measurements often accommodate psychoacoustic principles to measure the system in a way that relates to human hearing.
Dolby Pro Logic is a surround sound processing technology developed by Dolby Laboratories, designed to decode soundtracks encoded with Dolby Surround. The terms Dolby Stereo and LtRt are also used to describe soundtracks that are encoded using this technique.
A bass reflex system is a type of loudspeaker enclosure that uses a port (hole) or vent cut into the cabinet and a section of tubing or pipe affixed to the port. This port enables the sound from the rear side of the diaphragm to increase the efficiency of the system at low frequencies as compared to a typical sealed- or closed-box loudspeaker or an infinite baffle mounting.
A tactile transducer or "bass shaker" is a device which is made on the principle that low bass frequencies can be felt as well as heard. They can be compared with a common loudspeaker, just that the diaphragm is missing. Instead, another object is used as a diaphragm. A shaker transmits low-frequency vibrations into various surfaces so that they can be felt by people. This is called tactile sound. Tactile transducers may augment or in some cases substitute for a subwoofer. One benefit of tactile transducers is they produce little or no noise, if properly installed, as compared with a subwoofer speaker enclosure.
A loudspeaker enclosure or loudspeaker cabinet is an enclosure in which speaker drivers and associated electronic hardware, such as crossover circuits and, in some cases, power amplifiers, are mounted. Enclosures may range in design from simple, homemade DIY rectangular particleboard boxes to very complex, expensive computer-designed hi-fi cabinets that incorporate composite materials, internal baffles, horns, bass reflex ports and acoustic insulation. Loudspeaker enclosures range in size from small "bookshelf" speaker cabinets with 4-inch (10 cm) woofers and small tweeters designed for listening to music with a hi-fi system in a private home to huge, heavy subwoofer enclosures with multiple 18-inch (46 cm) or even 21-inch (53 cm) speakers in huge enclosures which are designed for use in stadium concert sound reinforcement systems for rock music concerts.
Sound Blaster Live! is a PCI add-on sound card from Creative Technology Limited for PCs. Moving from ISA to PCI allowed the card to dispense with onboard memory, storing digital samples in the computer's main memory and then accessing them in real time over the bus. This allowed for a much wider selection of, and longer playing, samples. It also included higher quality sound output at all levels, quadrophonic output, and a new MIDI synthesizer with 64 sampled voices. The Live! was introduced in August 1998 and variations on the design remained Creative's primary sound card line into the early 2000's.
A Linkwitz–Riley (L-R) filter is an infinite impulse response filter used in Linkwitz–Riley audio crossovers, named after its inventors Siegfried Linkwitz and Russ Riley. This filter type was originally described in Active Crossover Networks for Noncoincident Drivers in the Journal of the Audio Engineering Society. It is also known as a Butterworth squared filter. A Linkwitz–Riley "L-R" crossover consists of a parallel combination of a low-pass and a high-pass L-R filter. The filters are usually designed by cascading two Butterworth filters, each of which has −3 dB gain at the cut-off frequency. The resulting Linkwitz–Riley filter has −6 dB gain at the cut-off frequency. This means that, upon summing the low-pass and high-pass outputs, the gain at the crossover frequency will be 0 dB, so the crossover behaves like an all-pass filter, having a flat amplitude response with a smoothly changing phase response. This is the biggest advantage of L-R crossovers compared to even-order Butterworth crossovers, whose summed output has a +3 dB peak around the crossover frequency. Since cascading two nth-order Butterworth filters will give a (2n)th-order Linkwitz–Riley filter, theoretically any (2n)th-order Linkwitz–Riley crossover can be designed. However, crossovers of order higher than 4 may have less usability due to their complexity and the increasing size of the peak in group delay around the crossover frequency.
An audio/video receiver (AVR) is a consumer electronics component used in a home theater. Its purpose is to receive audio and video signals from a number of sources, and to process them and provide power amplifiers to drive loudspeakers and route the video to displays such as a television, monitor or video projector. Inputs may come from a satellite receiver, radio, DVD players, Blu-ray Disc players, VCRs or video game consoles, among others. The AVR source selection and settings such as volume, are typically set by a remote controller.
Bi-amping and tri-amping is the practice of using two or three audio amplifiers respectively to amplify different audio frequency ranges, with the amplified signals being routed to different speaker drivers, such as woofers, subwoofers and tweeters. With bi-amping and tri-amping, an audio crossover is used to divide a sound signal into different frequency ranges, each of which is then separately amplified and routed to separate speaker drivers. In Powered speakers using bi-amping, multiple speaker drivers are in the same speaker enclosure. In some bi-amp set-ups, the drivers are in separate speaker enclosures, such as with home stereos that contain two speakers and a separate subwoofer.
The Digital Sound System 80, short DSS80, was a three-piece PC audio system co-developed by Microsoft and Philips. It debuted on the 1998 Electronic Entertainment Expo (E³) and is most likely the only speaker system ever released by the Microsoft Corporation. It also remains one of the very few featuring Philips' wOOx subwoofer technology.
Acoustic suspension is a method of loudspeaker cabinet design and utilisation that uses one or more loudspeaker drivers mounted in a sealed box or cabinet. Acoustic suspension systems reduce bass distortion that can be caused by stiff motor suspensions in conventional loudspeakers.
A stage monitor system is a set of performer-facing loudspeakers called monitor speakers, stage monitors, floor monitors, wedges, or foldbacks on stage during live music performances in which a sound reinforcement system is used to amplify a performance for the audience. The monitor system allows musicians to hear themselves and fellow band members clearly.
Equalization, or simply EQ, in sound recording and reproduction is the process of adjusting the volume of different frequency bands within an audio signal. The circuit or equipment used to achieve this is called an equalizer.
