FMX (broadcasting)
Encyclopedia
FMX is the name of a commercially unsuccessful noise reduction
system developed in the 1980s for FM broadcasting
in the United States.
FM stereo broadcasting is known to incur up to a 23 dB
noise
penalty over that of monophonic
FM broadcasting; this is due to the combination of the triangular FM
noise spectrum
and the wider baseband
bandwidth occupied by the stereo multiplex
signal. Developed at the CBS Technology Center
, FMX was intended to improve this characteristic for listeners in the fringe areas where the noise penalty would be worst. This improvement was achieved by adding an amplitude-compressed
version of the L−R (left-minus-right, or difference) signal modulated
in quadrature
with the stereo subcarrier
, using a version of the CX
noise-reduction system originally developed at CBS
for LP records
.
Upon his accession as Chairman of CBS, Laurence Tisch
closed the CBS labs in 1986, whereupon the FMX intellectual property
was spun off to an investment group, under the name Broadcast Technology Partners (BTP).
With about 50 stations using the technology and perhaps another 50 committed, a controversy emerged in 1989 when MIT professor and Bose Corporation CEO Amar Bose
and Bose engineer William Short released a critical study, finding the system to have the potential to "seriously degrade the quality of stereo reception whether received by FMX equipment or not." According to the study, the heavy compression of the L−R audio caused interference
in receivers under multipath conditions. A BTP spokesman rebutted the finding, saying that the Bose analysis exaggerated a "worst-case scenario", and actually employed "flawed mathematics" to attempt to prove their point. Perhaps not coincidentally, a patent
application filed earlier by Bose disclosed an invention whose implementation was incompatible with the adoption of FMX, while another – filed by Bose and Short around the time of the release of the critical study – sought to improve the performance of FMX under multipath conditions.
Despite industrial supporters in both the broadcast
and consumer electronics
industries, the system never achieved a critical mass, and faded into obscurity. However, numerous related patents have since been applied for or granted, referencing the original FMX patents.
Noise reduction
Noise reduction is the process of removing noise from a signal.All recording devices, both analogue or digital, have traits which make them susceptible to noise...
system developed in the 1980s for FM broadcasting
FM broadcasting
FM broadcasting is a broadcasting technology pioneered by Edwin Howard Armstrong which uses frequency modulation to provide high-fidelity sound over broadcast radio. The term "FM band" describes the "frequency band in which FM is used for broadcasting"...
in the United States.
FM stereo broadcasting is known to incur up to a 23 dB
Decibel
The decibel is a logarithmic unit that indicates the ratio of a physical quantity relative to a specified or implied reference level. A ratio in decibels is ten times the logarithm to base 10 of the ratio of two power quantities...
noise
Electronic noise
Electronic noise is a random fluctuation in an electrical signal, a characteristic of all electronic circuits. Noise generated by electronic devices varies greatly, as it can be produced by several different effects...
penalty over that of monophonic
Monaural
Monaural or monophonic sound reproduction is single-channel. Typically there is only one microphone, one loudspeaker, or channels are fed from a common signal path...
FM broadcasting; this is due to the combination of the triangular FM
Frequency modulation
In telecommunications and signal processing, frequency modulation conveys information over a carrier wave by varying its instantaneous frequency. This contrasts with amplitude modulation, in which the amplitude of the carrier is varied while its frequency remains constant...
noise spectrum
Spectrum
A spectrum is a condition that is not limited to a specific set of values but can vary infinitely within a continuum. The word saw its first scientific use within the field of optics to describe the rainbow of colors in visible light when separated using a prism; it has since been applied by...
and the wider baseband
Baseband
In telecommunications and signal processing, baseband is an adjective that describes signals and systems whose range of frequencies is measured from close to 0 hertz to a cut-off frequency, a maximum bandwidth or highest signal frequency; it is sometimes used as a noun for a band of frequencies...
bandwidth occupied by the stereo multiplex
Multiplexing
The multiplexed signal is transmitted over a communication channel, which may be a physical transmission medium. The multiplexing divides the capacity of the low-level communication channel into several higher-level logical channels, one for each message signal or data stream to be transferred...
signal. Developed at the CBS Technology Center
CBS Laboratories
CBS Laboratories or CBS Labs was the technology research and development organization of CBS...
, FMX was intended to improve this characteristic for listeners in the fringe areas where the noise penalty would be worst. This improvement was achieved by adding an amplitude-compressed
Audio level compression
Dynamic range compression, also called DRC or simply compression reduces the volume of loud sounds or amplifies quiet sounds by narrowing or "compressing" an audio signal's dynamic range...
version of the L−R (left-minus-right, or difference) signal modulated
Modulation
In electronics and telecommunications, modulation is the process of varying one or more properties of a high-frequency periodic waveform, called the carrier signal, with a modulating signal which typically contains information to be transmitted...
in quadrature
Quadrature amplitude modulation
Quadrature amplitude modulation is both an analog and a digital modulation scheme. It conveys two analog message signals, or two digital bit streams, by changing the amplitudes of two carrier waves, using the amplitude-shift keying digital modulation scheme or amplitude modulation analog...
with the stereo subcarrier
Subcarrier
A subcarrier is a separate analog or digital signal carried on a main radio transmission, which carries extra information such as voice or data. More technically, it is an already-modulated signal, which is then modulated into another signal of higher frequency and bandwidth...
, using a version of the CX
CX (audio)
CX is a noise reduction system for recorded analog audio. It was developed by CBS Laboratories in the early 1980s, as a competitor to other noise reduction systems such as Dolby and dbx...
noise-reduction system originally developed at CBS
CBS
CBS Broadcasting Inc. is a major US commercial broadcasting television network, which started as a radio network. The name is derived from the initials of the network's former name, Columbia Broadcasting System. The network is sometimes referred to as the "Eye Network" in reference to the shape of...
for LP records
Gramophone record
A gramophone record, commonly known as a phonograph record , vinyl record , or colloquially, a record, is an analog sound storage medium consisting of a flat disc with an inscribed, modulated spiral groove...
.
Upon his accession as Chairman of CBS, Laurence Tisch
Laurence Tisch
Laurence Alan "Larry" Tisch was an American businessman, Wall Street investor and self-made billionaire. He was the CEO of CBS television network from 1986 to 1995...
closed the CBS labs in 1986, whereupon the FMX intellectual property
Intellectual property
Intellectual property is a term referring to a number of distinct types of creations of the mind for which a set of exclusive rights are recognized—and the corresponding fields of law...
was spun off to an investment group, under the name Broadcast Technology Partners (BTP).
With about 50 stations using the technology and perhaps another 50 committed, a controversy emerged in 1989 when MIT professor and Bose Corporation CEO Amar Bose
Amar Bose
Amar Gopal Bose is an Bengali American electrical engineer, sound engineer and billionaire entrepreneur. He is the founder and chairman of Bose Corporation...
and Bose engineer William Short released a critical study, finding the system to have the potential to "seriously degrade the quality of stereo reception whether received by FMX equipment or not." According to the study, the heavy compression of the L−R audio caused interference
Interference (communication)
In communications and electronics, especially in telecommunications, interference is anything which alters, modifies, or disrupts a signal as it travels along a channel between a source and a receiver. The term typically refers to the addition of unwanted signals to a useful signal...
in receivers under multipath conditions. A BTP spokesman rebutted the finding, saying that the Bose analysis exaggerated a "worst-case scenario", and actually employed "flawed mathematics" to attempt to prove their point. Perhaps not coincidentally, a patent
Patent
A patent is a form of intellectual property. It consists of a set of exclusive rights granted by a sovereign state to an inventor or their assignee for a limited period of time in exchange for the public disclosure of an invention....
application filed earlier by Bose disclosed an invention whose implementation was incompatible with the adoption of FMX, while another – filed by Bose and Short around the time of the release of the critical study – sought to improve the performance of FMX under multipath conditions.
Despite industrial supporters in both the broadcast
Broadcast
Broadcast or Broadcasting may refer to:* Broadcasting, the transmission of audio and video signals* Broadcast, an individual television program or radio program* Broadcast , an English electronic music band...
and consumer electronics
Consumer electronics
Consumer electronics are electronic equipment intended for everyday use, most often in entertainment, communications and office productivity. Radio broadcasting in the early 20th century brought the first major consumer product, the broadcast receiver...
industries, the system never achieved a critical mass, and faded into obscurity. However, numerous related patents have since been applied for or granted, referencing the original FMX patents.