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Stereophonic systems (information storage on discs or tapes G11B; broadcast systems for the distribution of stereophonic information H04H 20/88; multiplex systems in general H04J)
Definition statement
This subclass/group covers:

Signal processing or circuitry for stereophonic sound reproduction, using loudspeakers or headphones, or for stereophonic sound capturing.

References relevant to classification in this subclass
This subclass/group does not cover:
Speech or audio signal analysis-synthesis techniques for redundancy reduction, e.g. in vocoders ; Coding or decoding of speech or audio signals, e.g. for compression or expansion, source-filter models or psychoacoustic analysis
Multi-channel audio coding and decoding using interchannel correlation to reduce redundancies
G10L19/00M
Informative references
Attention is drawn to the following places, which may be of interest for search:
Information storage on discs or tapes
Low frequency amplifiers, e.g. audio preamplifiers
Power amplifiers using a combination of several semiconductor amplifiers
Combinations of amplifiers using coupling networks with distributed constants
Combinations of amplifiers, e.g. multi-channel amplifiers for stereophonics
Remote control of amplification, tone, or bandwidth
Gain control
Tone control and equalizers
Compression or expansion
Combination of types of control
Broadcast systems for the distribution of stereophonic information
Multiplex systems in general
Stereophonic arrangements of loudspeakers, microphones or headphones
Sound processing hardware for games using an electronically generated display having two or more dimensions
Special rules of classification within this subclass

Classification of invention information and additional information is obligatory.

Further detail not provided for in any of the main groups is provided for in the subgroups of Indexing Code groups H04S 2400/00 and H04S 2420/00. Classification is obligatory.

Indexing Code symbols of the type H04S4xx should be used to classify information relevant for the invention, although it need not be invention information.

Indexing Code groups H04S 2400/00 and H04S 2420/00 should not be used for classification.

Two-channel systems (H04S 5/00, H04S 7/00 take precedence)
Definition statement
This subclass/group covers:

Non-adaptive circuits, i.e. manually adjustable or static, signal processing, e.g. for enhancing the sound image or the spatial distribution, or for sound capture in two-channel systems.

References relevant to classification in this group
This subclass/group does not cover:
Pseudo-stereophonic systems
Indicating arrangements of stereophonic systems; Control arrangements, e.g. balance control of stereophonic systems
Special rules of classification within this group

Multi-channel, i.e. more than two input channels, sound reproduction with two speakers wherein the multi-channel information is substantially preserved is not to be classified under H04S 1/00 but under H04S 3/00, H04S 5/00 or H04S 7/00 using the Indexing Code H04S 2400/01.

Further detail is covered by the subgroups of Indexing Code group H04S 2400/00 and H04S 2420/00. Classification is obligatory.

[N: Non-adaptive circuits, e.g. manually adjustable or static, for enhancing the sound image or the spatial distribution (control circuits for electronic adaptation of the sound field H04S 7/30)]
Definition statement
This subclass/group covers:

Electronic sound processing for enhancing the sound image or the spatial distribution, wherein the processing itself is independent on the input signal or its properties.

See for example: WO2005009078

References relevant to classification in this subgroup
This subclass/group does not cover:
Control circuits for electronic adaptation of the sound field, i.e. electronic sound processing automatically adaptable in dependence of the input signal or some of its properties, e.g. by using an adaptive circuit or a look-up table, for changing the sound field, e.g. the spatial distribution
[N: in which the audio signals are in digital form (data reduction aspects thereof based on psychoacoustics G10L 19/02)]
References relevant to classification in this subgroup
This subclass/group does not cover:
Data reduction aspects of digital stereo signals based on psychoacoustics
Systems employing more than two channels, e.g. quadraphonic (H04S 5/00, H04S 7/00 take precedence)
Definition statement
This subclass/group covers:

Non-adaptive circuits, i.e. manually adjustable or static, for signal processing, e.g. enhancing the sound image or the spatial distribution, of for sound capture in multi-channel systems.

References relevant to classification in this group
This subclass/group does not cover:
Pseudo-stereophonic systems
Indicating arrangements of stereophonic systems; Control arrangements, e.g. balance control of stereophonic systems
Special rules of classification within this group

Further detail is covered by the subgroups of Indexing Code groups H04R 2203/00, H04S 2400/00 and H04S 2420/00. Classification is obligatory.

[N: Non-adaptive circuits, e.g. manually adjustable or static, for enhancing the sound image or the spatial distribution (control circuits for electronic adaptation of the sound field H04S 7/30)]
Definition statement
This subclass/group covers:

Electronic sound processing for enhancing the sound image or the spatial distribution, wherein the processing itself is independent on the input signal or its properties.

See for example: US5740253

References relevant to classification in this subgroup
This subclass/group does not cover:
Control circuits for electronic adaptation of the sound field, i.e. electronic sound processing automatically adaptable in dependence of the input signal or some of its properties, e.g. by using an adaptive circuit or a look-up table, for changing the sound field, e.g. the spatial distribution
[N: in which a plurality of audio signals are transformed in a combination of audio signals and modulated signals, e.g. CD-4 systems (for broadcasting H04H 20/88, H04B 1/1646)]
Informative references
Attention is drawn to the following places, which may be of interest for search:
For broadcasting
[N: in which the audio signals are in digital form, i.e. employing more than two discrete digital channels, e.g. Dolby Digital, Digital Theatre Systems (DTS) (data reduction aspects thereof based on psychoacoustics G10L 19/02)]
Definition statement
This subclass/group covers:

See for example: US2002159611

References relevant to classification in this subgroup
This subclass/group does not cover:
Data reduction aspects of digital stereo signals based on psychoacoustics
Informative references
Attention is drawn to the following places, which may be of interest for search:
Reduction of bandwidth of signals in transmission systems using psychoacoustic properties of the ear, e.g. masking effect.
of the matrix type, i.e. in which input signals are combined algebraically, e.g. after having been phase shifted with respect to each other
Definition statement
This subclass/group covers:

E.g. Dolby Surround, Pro-Logic, incl. AC-1

See for example: US5771295

Pseudo-stereo systems, e.g. in which additional channel signals are derived from monophonic signals by means of phase shifting, time delay or reverberation (arrangements for producing a reverberation or echo sound G10K 15/08)
Definition statement
This subclass/group covers:

Systems wherein additional channels are generated from the existing channels to improve the spatial sound reproduction, e.g. wave field synthesis or virtual surround sound, or the spatial sound capture, e.g. 4-channel ambisonic capture to 7.1-channel

Informative references
Attention is drawn to the following places, which may be of interest for search:
Arrangements for producing a reverberation or echo sound
Special rules of classification within this group

Further detail is covered by the subgroups of Indexing Code group H04S 2400/00 and H04S 2420/00. Classification is obligatory.

[N: of the pseudo five- or more-channel type, e.g. virtual surround]
Definition statement
This subclass/group covers:

See for example: US5295189

Indicating arrangements; Control arrangements, e.g. balance control
Definition statement
This subclass/group covers:

Sound field processing, i.e. electronic adaptation of the sound field e.g. automatic set-up, adaptation with respect to listener position, frequency adjustment, reverberation adaptation, sound object positioning.

Indicating of the sound field.

References relevant to classification in this group
This subclass/group does not cover:
Non-adaptive circuits, i.e. manually adjustable or static, for signal processing, e.g. enhancing the sound image or the spatial distribution, of for sound capture in stereophonic systems
Informative references
Attention is drawn to the following places, which may be of interest for search:
Arrangements for producing a reverberation or an echo sound
Tone control circuits in amplifiers per se
Circuits for coupling gramophone pick-up, recorder output, or microphone to receiver, e.g. for Hi-Fi systems or audio/video combinations by remote control
Circuits for correcting the frequency response of transducers
Adaptation of reverberation in public address systems
Monitoring or testing arrangements for transducers, loudspeakers, microphones or public address systems; Visual indication of acoustic signal levels
Special rules of classification within this group

Further detail is covered by the subgroups of Indexing Code groups H04R 2203/00, H04S 2400/00 and H04S 2420/00. Classification is obligatory.

Groups H04S 7/30 to H04S 7/40 do not correspond to former or current IPC groups. The concordance ECLA : IPC for these groups is as follows: H04S 7/30-H04S 7/40 : H04S 7/00

[N: Control circuits for electronic adaptation of the sound field (non-adaptive circuits, i.e. manually adjustable or static, for enhancing the sound image or the spatial distribution H04S 1/002, H04S 3/002)]
Definition statement
This subclass/group covers:

Electronic sound processing automatically adaptable in dependence of the input signal or some of its properties, e.g. by using an adaptive circuit or a look-up table, for changing the sound field, e.g. the spatial distribution.

See for example: EP1473971

References relevant to classification in this subgroup
This subclass/group does not cover:
Telephonic conference arrangements
Video conference systems
Non-adaptive circuits, i.e. manually adjustable or static, for enhancing the sound image or the spatial distribution
[N: Automatic calibration of stereophonic sound system, e.g. with test microphone]
Definition statement
This subclass/group covers:

See for example: US5666424 and US2002159611

Informative references
Attention is drawn to the following places, which may be of interest for search:
Automatic gain control
Automatic tone control or bandwidth control in amplifiers
[N: Electronic adaptation of stereophonic sound system to listener position or orientation (H04S 7/301 takes precedence)]
Definition statement
This subclass/group covers:

See for example: WO0241664, US6108430 and EP1482763

References relevant to classification in this group
This subclass/group does not cover:
Automatic calibration of stereophonic sound system, e.g. with test microphone
[N: Tracking of listener position or orientation]
Informative references
Attention is drawn to the following places, which may be of interest for search:
Head tracking input arrangements for transferring data to be processed into a form capable of being handled by the computer
[N: Electronic adaptation of stereophonic audio signals to reverberation of the listening space (H04S 7/301 takes precedence; arrangements for producing a reverberation or echo sound G10K 15/08; for public address systems H04R 27/00, H04R 29/00)]
Definition statement
This subclass/group covers:

See for example: EP1341399 (room) and EP1482763 (vehicle)

References relevant to classification in this group
This subclass/group does not cover:
Automatic calibration of stereophonic sound system, e.g. with test microphone
Informative references
Attention is drawn to the following places, which may be of interest for search:
Measuring reverberation time, i.e. room acoustic measurements
Arrangements for producing a reverberation or echo sound
For public address systems
T04R27/007
[N: Frequency adjustment, e.g. tone control (H04S 7/301 takes precedence; circuits for correcting the frequency response of transducers H04R 3/04 ; tone control circuits in amplifiers per se H03G 5/00)]
Definition statement
This subclass/group covers:

See for example: US5325435.

References relevant to classification in this group
This subclass/group does not cover:
Automatic calibration of stereophonic sound system, e.g. with test microphone
Informative references
Attention is drawn to the following places, which may be of interest for search:
Tone control in general
Circuits for correcting the frequency response of transducers
[N: Electronic adaptation dependent on speaker or headphone connection]
Definition statement
This subclass/group covers:

See for example: WO2006033058

Visual indication of stereophonic sound image
Definition statement
This subclass/group covers:

See for example: WO2006033058 and US2004264704

Informative references
Attention is drawn to the following places, which may be of interest for search:
Indicating measured values
Arrangements for displaying electric variables or waveforms
Visual indication of individual signal levels
Beamforming aspects for stereophonic sound reproduction with loudspeaker arrays
Definition statement
This subclass/group covers:

See for example: US2004151325 (see e.g. Figs.8 and 23, paragraphs [0175], [0176], [0235] and [0236]).

Acoustic transducers or sound field adaptation in vehicles
Informative references
Attention is drawn to the following places, which may be of interest for search:
Mounting of acoustic transducers in vehicles
Automatic control of amplifiers dependent upon ambient noise level or sound level

See for example: US6389147 and EP1482763

Glossary of terms
In this subclass/group, the following terms (or expressions) are used with the meaning indicated:
Stereophonic system
two- or more channel system, e.g. quadraphonic, ambisonic or similar systems
Multi-channel system
three- or more channel system
Multi-channel, i.e. more than two input channels, sound reproduction with two speakers wherein the multi-channel information is substantially preserved
Informative references
Attention is drawn to the following places, which may be of interest for search:
Aspects of down-mixing multi-channel audio to configurations with lower numbers of playback channels, e.g. 7.1 -> 5.1
Special rules of classification within this group

NOT to be given for H04S 1/00 since no multi-channel sound information is present according to H04S 1/00. See for example: US6470087, US5912976

Aspects of down-mixing multi-channel audio to configurations with lower numbers of playback channels, e.g. 7.1 -> 5.1 (H04S 2400/01 takes precedence)
References relevant to classification in this group
This subclass/group does not cover:
Multi-channel, i.e. more than two input channels, sound reproduction with two speakers wherein the multi-channel information is substantially preserved

See for example: US2008049943 (e.g. paragraphs [0098] - [0099] and Figs.6A and 6B).

Generation or adaptation of centre channel in multi-channel audio systems
Informative references
Attention is drawn to the following places, which may be of interest for search:
Generation of additional channels in pseudo stereo system per se
Adaptation of sound field per se

See for example: EP0526136

Generation or adaptation of the Low Frequency Effect [LFE] channel, e.g. distribution or signal processing
Definition statement
This subclass/group covers:

See for example: EP0854660 (Figs.1-3; distribution, and Figs.5 and 6; signal processing).

Electronic reduction of distortion of stereophonic sound systems
Informative references
Attention is drawn to the following places, which may be of interest for search:
Reduction of non-linear distortion in audio amplifiers

See for example: US6519344

Positioning of individual sound objects, e.g. moving airplane, within a sound field (H04S 2420/13 takes precedence)
Informative references
Attention is drawn to the following places, which may be of interest for search:
Positioning of sound field itself, e.g. balance and fading
Aspects of volume control, not necessarily automatic, in two- and multi-channel sound systems

See for example: US6519344

Glossary of terms
In this subclass/group, the following terms (or expressions) are used with the meaning indicated:
Sound object
audio object, i.e. acoustic representation of a sound producing entity in a sound field
Sound source
real or virtual loudspeaker
Synonyms and Keywords

In patent documents the expressions/words "virtual sound sources", "virtual sound objects" and "virtual loudspeakers" are often used as synonyms.

Aspects of volume control, not necessarily automatic, in stereophonic sound systems
Informative references
Attention is drawn to the following places, which may be of interest for search:
Control of amplification per se

See for example: US2004213421 and DE4202609

Aspects of sound capture and related signal processing for recording or reproduction
Informative references
Attention is drawn to the following places, which may be of interest for search:
Spatial or contructional arrangements of microphones

See for example: US2005141728 (Figs. 3, 5 and 6) and US2006206221 (Figs.1 and 3)

Special rules of classification within this group

Documents only relating to spatial or construction arrangements of microphones should not receive this Indexing Code group

Enhancing the perception of the sound image or of the spatial distribution using head related transfer functions [HRTF’s] or equivalents thereof, e.g. interaural time difference [ITD] or interaural level difference [ILD]
Definition statement
This subclass/group covers:

See for example: US6466913, US6243476 and DE102004035046

Application of parametric coding in stereophonic audio systems
Informative references
Attention is drawn to the following places, which may be of interest for search:
Parametric coding as such
G10L19/00M

See for example: WO2005094125

Application of the precedence or Haas effect, i.e. the effect of first wavefront, in order to improve sound-source localisation
Definition statement
This subclass/group covers:

See for example: EP1771039

Synergistic effects of band splitting and subband processing
Informative references
Attention is drawn to the following places, which may be of interest for search:
Digital filter banks
Crossover filters for loudspeakers

See for example: EP1471765, US4953216 and DE19632734

Special rules of classification within this group

The mere band splitting or presence of a filter bank (e.g. FFT, FIR, ...) should not be classified in this Indexing Code group

Application of ambisonics in stereophonic audio systems
Definition statement
This subclass/group covers:

See for example: US3997725 and US5757927

Application of wave-field synthesis in stereophonic audio systems
Definition statement
This subclass/group covers:

See for example: WO2004103022

Glossary of terms
In this subclass/group, the following terms (or expressions) are used with the meaning indicated:
Control systems
encompasses adaptive systems
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Last Modified: 10/11/2013