Patent Description:
Embodiments relate to audio systems, and more specifically to clock synchronization for transmitting digital audio and power over a common conductor.

The transmission of digital audio data via the Ethernet has long been a subject of discussion and development in the audio industry. The most common present approach is that defined in the AES67 standard, which defines audio over Internet Protocol (IP) and audio over Ethernet (AoE) interoperability. This approach provides mechanisms to transmit the audio sample streams and the audio clocking to recover, decode, and time align the samples at an audio end-point. To establish a reliable technique for synchronizing the audio clocks via Ethernet, AES67 utilizes the IEEE1588 standard for Precision Time Protocol (PTP) packets. This technique is a packetized clock format wherein the end-points (slaves) can receive specific PTP packets and ultimately synchronize to the master clock that was originated in the master transmitter. The AES67 standard, and similar methods, rely upon Ethernet packets to transmit and receive clocking information such that the end-points (slaves) can synchronize to the master clock.

Along with AoE development, Power-Line Communication (PLC) technology has also evolved considerably over the past decade and today has reliably demonstrated <NUM> Gigabit data transmission performance over standard AC mains power line infrastructure. The basic approach used by PLC devices is to transmit digital data using multiple frequencies positioned well-above the base-band power transmission spectrum. Thus, the two transmissions paths, one power path and one digital data path, can coexist on the same power line or loudspeaker cable infrastructure. PLC technology relies on digital communication practices such as Orthogonal Frequency Division Multiplexing (OFDM) and Bi-Polar Phase Shift Keying (BPSK) to transmit the digital data on a basic two-conductor power line. Such techniques fundamentally require synchronization between the master transmitter and the downstream end-point (slaves). Thus, present PLC standards (e.g., Homeplug AV2, ITU-T, G. Hn and IEEE1901-<NUM>) require robust mechanisms for establishing clock synchronization between transmit and receive nodes residing on the power line bus.

In general, the AES67 approach does not perform well when subjected to latent or jittery Ethernet packets, which is the case when passing such packets through PLC devices. Thus, systems that use packet-based clock synchronization schemes, such as AES67 are not reliable when passing through PLC transmission and reception infrastructure.

<CIT> discloses a method and apparatus for synchronizing streaming media devices within a PLC network. <CIT> discloses that output synchronization errors exceeding ~<NUM> become noticeable when multiple streaming media devices are outputting an audio stream. <CIT> discloses a system and method for isochronously sending periodic reference clocks from a master device to client devices coupled to the PLC network. <CIT> further discloses that the client devices set their clocks based on the reference clock, and in addition the clients adjust their system clock time base in response to the average divergence of the system clock with the reference clock, or a count of the number of clocks between beacon frames. , by way of which the client clock is adjusted to closely track the server clock so that synchronization is maintained between each of the devices. <CIT> discloses that streaming audio shared between servers and client devices is thus output across the network with high fidelity due to the accurate synchronization.

<CIT> discloses that a time synchronization beacon, which includes a plurality of timing signals at a plurality of different respective carrier frequencies, is synchronously transmitted over a power line network to synchronize consumption of media content data, such as audio data, which has been transmitted over the network from a power line communications ("PLC") audio source to PLC equipped media content consumption devices, such as stereo audio speaker sets. <CIT> discloses that the sets of speakers can be located in different respective rooms throughout a facility, and that the audio data can be in the form of network audio network data packets including one or more channels of audio data. <CIT> further discloses that the PLC consumption devices select which transmitted channel data is received and consumed, that the beacon coordinates the start time of consumption of segments of audio data samples, and the sample-to-sample consumption time interval at PLC equipped consumption devices, and that the network packets can be addressed for desired PLC consumption devices using PLC network addressing methods.

Embodiments include a distributed audio speaker system comprising an audio source and a plurality of end-points and a method of synchronizing timing of an audio source and a plurality of endpoints according to the appended claims.

In the following drawings like reference numbers are used to refer to like elements. Although the following figures depict various examples, the one or more implementations are not limited to the examples depicted in the figures.

Embodiments are directed to systems and methods for clock synchronization for transmitting digital audio over base-band power lines or speaker cables in audio playback systems. Any of the described embodiments may be used alone or together with one another in any combination. Although various embodiments may have been motivated by various deficiencies with the current and known solutions, which may be discussed in the specification, the embodiments do not necessarily address any of these deficiencies. Different embodiments may address different deficiencies, and some may only be partially addressed.

Developments in transmitting packetized digital audio data over power line and loudspeaker cabling for the past few years has led to systems that greatly simplify wiring, improve fidelity and performance, lower cost. One such development is a distributed amplification or "drive-pack" system in which multi-channel digital audio data and power signals are present on the speaker wiring routed to each drive-packs located at each speaker. These drive-packs can demodulate and decode the desired audio channel and recover the power signal, which will then be used to drive their respective loudspeaker. In an embodiment, this technology relies on concepts of power-line communications (PLC) technology to establish a reliable digital data link between the master transmitter and downstream receivers. Power transmission and recovery are established using audio-band signals and modulation techniques. The overall aim of this system is to create a loudspeaker amplification and drive system wherein a single cable can daisy-chain between multiple loudspeakers, yet each speaker can play unique content material.

<FIG> illustrates a distributed amplifier speaker system that implements one or more embodiments of a clock synchronization scheme for transmitting digital audio and power over common base-band power lines or speaker cables. As shown in <FIG>, system <NUM> is a multi-channel speaker system with any number, N, of speakers <NUM>. Instead of having one amplifier and one power supply and separate dedicated cabling per speaker channel as in traditional speaker hookups, system <NUM> features one main amplifier and associated control unit <NUM>, one cable run ("bus") <NUM>, and one power supply <NUM> for all of the N speaker channels <NUM>. To attain this simplification in the power and signal distribution infrastructure, each speaker channel has associated with it a dedicated speaker unit <NUM>, referred to as a "drivepack," that receives and recovers the power and audio signal that is generated by the control unit <NUM>. The number N channels can be any practical number of channels dictated by the system requirements. For a standard surround sound setup, N may be <NUM> or <NUM>, while for a full spatial audio (e.g., Dolby Atmos®) system with height speakers, N can be on the order of <NUM> or <NUM> channels or more.

The architecture of system <NUM> allows for audio power and signal to be distributed to multiple loudspeakers without the use of high channel-count amplifiers and multiple point-to-point cables, thus reducing the number of audio power amplifier channels and the number of independent loudspeaker cables, while still allowing each loudspeaker to have independent drive (i.e., separate audio signals present at each loudspeaker). In an embodiment, amplifier <NUM> is a power supply that may be implemented as a customized or standard audio amplifier to transmit a power signal over the bus <NUM>, and control unit <NUM> comprises an N-channel digital audio transceiver and an audio signal generator that adds a digital audio signal onto the same bus cable.

A digital audio transceiver of unit <NUM> transmits multiple digital audio streams in as driven by the power signal generated by the audio amplifier <NUM>. These two signal streams (power and data) are transmitted simultaneously through bus <NUM> and are received by small electronic speaker units <NUM> built in (or closely coupled) to each loudspeaker <NUM>. The speaker units <NUM> recover the power, receive the digital audio stream, and drive the loudspeakers with the selected signals. In one embodiment, the bus cable <NUM> is a single standard two-conductor speaker cable of standard gauge (e.g., <NUM>-<NUM> gauge) and can be used to send multiple channels of digital audio and appropriate power to independent loudspeakers connected to the same two-conductor cable. That is, many speakers can be wired in a daisy-chained or parallel fashion while still allowing independent channels of audio to be played at each speaker (i.e., different signals and volumes). The bus cable may be implemented as a simple two-conductor speaker cable or a three-conductor cable, such as an AC power cable where one conductor is an earth ground, or any other similar simple conductor cable. Instead of traditional speaker cable (i.e., stranded wire cable), a solid-core Romex (typical AC wiring cable) cable might be used as well.

In an embodiment, portions of power source <NUM> may be implemented as a standard power amplifier. This may also or instead be implemented as a dedicated base-band AC or DC power source, similar to an audio amplifier but with much higher power efficiency and power throughput. For this embodiment, the system would be highly suitable for maximum power transmission, minimized power loss, and lowest cost.

The loudspeakers <NUM> may represent a single driver or transducer within a single enclosure (cabinet), or a multi-driver loudspeaker with different transducers handling different audio components (e.g., woofer, midrange, tweeter), or arrays of speakers. In an embodiment, the speaker units <NUM> can also include additional circuitry to drive each speaker component independently (e.g., woofer, tweeter, etc.) in a bi-amplification system. Both the control unit and each speaker unit include a transceiver stage allowing for bidirectional data flow between the digital audio transceiver of the control unit and the multiple speakers residing on the bus. Thus, other pieces of information can be propagated to-and-from the loudspeaker. For example, a loudspeaker could report telemetry (e.g., down-angle, temperature, etc.), and/or setup information could be sent to individual speakers (e.g., volume control, angle adjustment for motorized pan-tilt, and so on). In systems utilizing bi-amplification within the speaker, derivation of two (or more) audio signals can be done by sending the speaker unit <NUM> a single audio stream, wherein the speaker unit employs signal processing to derive two (or more) audio signals from a single input stream. The control unit <NUM> may also send the multiple streams directly to the individual amplification stages within the speaker unit <NUM>.

<FIG> illustrates components of control and speaker units for the distributed amplification system of <FIG> under some embodiments. The architecture of the system <NUM> subdivides the audio amplification process such that the power supply is physically separated from the individual output stages and is chosen such that it effectively supplies an AC stimulus to power multiple output stages.

In an embodiment, power source <NUM> comprises a standard audio amplifier to provide power for other distributed audio output stages. This helps achieve an efficiency through component reuse by eliminating one of the largest cost drivers in any audio amplifier design, i.e., the power supply. An audio power amplifier is typically designed as an AC-DC power supply, feeding into one or more low-impedance, transistorized, output stages. Most audio amplifiers are designed as two to four-channel devices, wherein there is a singular power supply (AC/DC offline supply) fanning out to power the output stages. The power supply can thus be implemented as a standard audio amplifier that develops a controlled, audio-band, AC waveform, and provide regulatory compliance (e.g., NRTL, CE, FCC, safety isolation, etc.).

For the embodiment of <FIG>, the modulating input waveform applied to the power source audio amplifier is generated by an audio signal generator in control unit <NUM>. Because the output of the power source amplifier is used only for distributing power to the various output stages, no significant fidelity or spectral-purity requirement is imposed upon this power amplifier. Similar to the signals present on typical AC mains (120Vrms, <NUM>); the power source audio amplifiers would generate an AC waveform configured to power downstream distributed audio output stages. This allows an existing audio amplifier to serve as the power source for a distributed array of output stages, and a single cable <NUM> can power multiple output stages <NUM>. As with any paralleled power distribution system, the overall power consumption would have to be adequately determined and managed, such that the power source amplifier and cabling could adequately deliver the power as needed by the sum total of all distributed output stages connected to the line. In cases where more power is needed, or a greater number of paralleled output stages are attached to the line, the power source amp could be bridged or paralleled with a like amplifier. An example power supply may be a cinema-grade amplifier (e.g., Crown DSi2000) that delivers 800W per channel into <NUM> ohms or 1000W per channel into <NUM> ohms, or any similarly rated amplifier.

As shown in system <NUM>, the control unit <NUM> generates digital audio signals that comprises immersive audio having both channel-based and object-based audio components. For the example of <FIG>, an interface couples the control unit <NUM> to a renderer (e.g., CP850) <NUM>, for example. This interface and processor provide the signal to an audio signal generator that stimulates the power source <NUM>. A digital audio transmitter <NUM> of the control unit <NUM> outputs the digital audio signal directly to the output of the power source so that both power and the digital audio signal are carried on the bus cable <NUM>. The control unit also includes appropriate circuitry that conditions the power and data to endure that they are properly transmitted over the bus in terms of timing, amplitude, and phase.

Although embodiments are illustrated with respect to immersive or adaptive audio applications, it should be noted that any appropriate audio format may be used, and that, depending on the type of interface provided in control unit <NUM>, the input audio may be straight digital audio, hybrid audio, pure channel-based audio, pure object-based audio, and so on. In the case where analog audio is provided, the system may include an integrated or separate analog-digital converter to provide the digital audio signal to stimulate the power supply <NUM> and provide digital audio input to the bus cable <NUM>. In an embodiment, the control unit <NUM> outputs digital data primarily to be coupled into the output of the power source, and input to the power source is stimulated with an analog audio-band modulation signal (i.e., sine wave, pink-noise, summed audio signal, etc.). Thus, digital data is primarily routed/coupled to the output of the power source, whereas the input to the power source can be controlled via digital or analog techniques.

In an embodiment in which the power source <NUM> comprises a standard or other type of amplifier, the system <NUM> can be configured to create power stimulus signals into the amplifier as well as having a line connected to the output of the amplifier to inject the digital data stream onto the speaker wire or bus cable <NUM>. The digital data stream wire can also be used as a sense line for the controller through an A/D (analog/digital) circuit. The controller <NUM> can then compare the input and output signals coming from the respective amplifier channel. This allows additional features to be implemented in the software (or equivalent circuitry) such as gain modification adjustment (e.g., if the user changes the amplifier gain, the system can adjust the input signal to compensate), fault monitoring for distortion, fault monitoring for signal present, automated system configuration to alter gain structure, and other similar functions.

In an embodiment, the bus cable <NUM> that links the control unit <NUM> to each of the speaker units <NUM> is a single two-conductor speaker cable (or three-conductor power cable or similar). Data is transmitted over the bus using Internet Protocol (IP) conventions, though other protocols are also possible. A standard power-line communication format is utilized to provide sufficient bandwidth and channel separation to allow the channelized audio information produced by the control unit to be delivered to the output stages. Examples of standard power-line communication protocol include IEEE <NUM> (HomePlug AV <NUM>) and the G. hn protocol. It should be noted that embodiments are not so limited, and other standardized protocols, or proprietary techniques for transmitting digital audio information over power source cabling to deliver independent audio streams to distributed output stages are also possible.

The power signal, digital audio signal and metadata for audio object control and lighting control are transmitted over the same conductor between the control unit/amplifier and the speaker units, and are encoded in different bands of the frequency spectrum. The power and audio signals may be separated by frequency band. For example, the power component may be relegated to a relatively low frequency band of between <NUM> (DC) and <NUM>, while the digital data component for the audio and lighting control may be carried in a band stretching between <NUM> to <NUM>, as an example, though embodiments are not so limited. <FIG> illustrates an example spectrum allocation for power and audio signals transmitted over the same conductors, under some embodiments. The spectrum allocation graph shows the amplitude (y-axis) <NUM> of signals versus their frequency (x-axis) <NUM>. As shown in <FIG>, the audio band power signal is encoded in the region of <NUM> to <NUM>, while the digital audio transmission is encoded in the region of <NUM> to <NUM>. The separation of the power <NUM> and audio <NUM> signals is thus on the order of greater than <NUM>. <FIG> illustrates an example power/audio spectrum allocation and embodiments are not so limited, as any other similar spectrum allocation may also be utilized to encode audio signals for transmission over common conductors.

<FIG> illustrates the distributed amplifier system of <FIG> as implemented using standard, commercially available components, under an example embodiment. For system <NUM>, audio and power signals are propagated between a source <NUM> and an endpoint <NUM> through certain electrical components per a specific sequence and over a common conductor <NUM>. Audio signals are originated from the audio block <NUM> of source <NUM>. The audio is then packetized into an Ethernet audio format (e.g., either AES67 or CobraNet) using an audio transmitter (e.g., Dolby CP850, Audio Science Hono <NUM>, or similar) <NUM>. The packetized audio is then sent to a Power-Line Communications (PLC) transmitter <NUM>, which is coupled to the output of a base-band power source (e.g., Crown amplifier) <NUM>. Amplifier <NUM> is driven by the audio signal from source <NUM> processed by a digital signal process (DSP) <NUM>. The amplifier <NUM> then outputs a power supply signal to be conducted via a standard two-conductor loudspeaker wiring, or other similar conductor or cable <NUM> to the end-point electronics located at or closely coupled to the loudspeaker <NUM>. The power supply signal output from the amplifier <NUM> and the packetized audio output from the PLC transmitter <NUM> are combined at the electrically coupled outputs of the PLC transmitter <NUM> and amplifier <NUM>.

Within the end-point <NUM>, a Power-Line Communication (PLC) receiver <NUM> is coupled to the inbound speaker wiring <NUM> and operable to demodulate and recover the Ethernet packets. The recovered Ethernet packets are then passed to an Ethernet audio receiver <NUM>, which recovers the audio stream that originated from the original audio source <NUM>. The recovered audio is then amplified using a standard or customized Class-D amplifier <NUM> for driving the loudspeaker transducer <NUM>. Amplifier <NUM> also receives as an input the composite signal transmitted over conductor <NUM> as conditioned or converted by a Power Factor Correction (PFC) component <NUM>.

<FIG> is provided only for the purpose of illustrating an example implementation of a distributed amplifier speaker system that includes or is modified to include a clock synchronization process. Such an example circuit is not intended to be limiting, and other implementations, components, configurations, and signal processing sequences are also possible.

As described previously, certain issues may exist with present PLC systems with respect to establishing reliable audio transmission from the audio source <NUM> to the end-point audio receiver <NUM>. The PLC transmission and reception process can add latency and jitter to the packetized digital information and resulting in decoding errors within the end-point. Of specific concern is the impact of the randomized PLC latency and jitter upon the packetized audio clocking infrastructure that is inherently embedded into the Ethernet audio schemes employed in certain audio over Ethernet systems. The PLC latency and jitter can adversely affect the reliable recovery and synchronization of the audio clocking information that is packetized within certain AoE streams, thus leading to poor transmission of Ethernet packetized audio streams through standard PLC devices. Specifically, it has been determined that certain latency and jitter added by the PLC transmission and reception process to the packetized digital information can result in decoding errors within the end-point <NUM>.

Embodiments thus include a clock synchronization and alignment component or system <NUM> that helps achieve satisfactory transmission of Ethernet packetized audio streams through standard PLC devices and common conductors (e.g., speaker wires).

As shown in <FIG>, a distributed amplifier audio transmission and speaker playback system incorporates a clock synchronization and alignment component <NUM> to help achieve clock synchronization and alignment for use with packetized audio transmissions over base-band power lines or speaker cables. This component or processes embodied therein helps solve the issues associated with poor clock synchronization when transmitting standardized audio packets using power-line communication devices.

<FIG> illustrates adding end-point audio clock synchronization through PLC clocking to the distributed amplifier system of <FIG>, under some embodiments. The approach of system <NUM> uses a hybrid combination of the two communication layers (e.g., AES67 and PLC) to provide a stable and reliable clock synchronization scheme for audio transmission over base-band power-lines. System <NUM> comprises a source circuit <NUM> with the audio source generating packetized Ethernet signals for transmission over conductor <NUM> to end-point <NUM> for playback through speaker <NUM>, as described above with respect to <FIG>. For this embodiment, the clock synchronization and alignment component <NUM> is embodied by clock circuit <NUM> for source 401and clock circuit <NUM> for end-point <NUM>.

For the embodiment of <FIG>, a singular master clock <NUM> is employed within the main transmitter, where this master clock synchronizes the Ethernet audio transmitter <NUM> with the PLC modulator <NUM>. Subsequently, the down-stream end-point <NUM> utilizes the PLC demodulation receiver <NUM> to recover and lock to the original master clock <NUM> and then feeds this synchronized clock to the Ethernet audio receiver <NUM>. This approach thus ensures reliable clock synchronization between the master transmitter and all down-stream end-points (slaves). Due to the inherent clock synchronization requirement of modern PLC transmissions utilizing OFDM and BPSK signaling, the master clock supplied to the PLC transmitter will be recovered by the downstream PLC receiver using phase-locking methods.

This clocking scheme also properly time aligns the clock edges to the inbound audio samples as recovered from the Ethernet data packets. This is accomplished by using the PLC telemetry information (received PLC symbol latency and jitter) to adequately adjust the recovered clock edge timing to align with the audio sample stream. Thus, the clocking mechanism of <FIG> accomplishes two goals. First, it provides clock recovery/synchronization between the source and the end-point (i.e. phase coherency is ensured between the audio source and the end-point), and second, it aligns the clock edge time with the audio sample stream. With these characteristics, reliable audio transmission can be realized using packetized audio over base-band power-line and loudspeaker cables.

<FIG> is a flowchart that illustrates a method of providing end-point audio clock synchronization through PLC clocking system, such as through the system of <FIG>, under some embodiments. Process <NUM> begins with providing a single master clock in or with the Ethernet transmitter of the source side, <NUM>. This master clock synchronizes the Ethernet transmitter with the PLC modulator of the source side, <NUM>. The synchronized PLC signal is then transmitted to the end-point side over the common connector (e.g., speaker wire), <NUM>. The PLC demodulation receiver of the end-point receives the PLC signal and recovers and locks to the original master clock, <NUM>. This recovered original master clock signal is then provided to the Ethernet audio receiver in the end-point, <NUM>. In this way, the master Ethernet transmitter's clock is synchronized with the Ethernet receiver of the end-point. In a speaker system with multiple (e.g., <NUM> to <NUM>) speakers, this scheme ensures that the clock is reliably synchronized between the master transmitter and all of the speaker end-points.

As stated above with respect to <FIG>, the PLC signal sent from the source to the end-point is also used to properly time align the clock edges to the inbound audio samples as recovered from the Ethernet data packets. Thus, in process <NUM>, the transmitted synchronized PLC signal (transmitted in step <NUM> of flow diagram of <FIG>) is also used to adequately adjust the recovered clock edge timing to align with the audio sample stream (aligned in step <NUM> of flow diagram of <FIG>). This is done using the received PLC symbol latency and jitter (PLC telemetry data) within the received PLC signal. By monitoring the symbol-to-symbol latency, delay, and nominal jitter performance of the physical layer (i.e., the loudspeaker cabling), the PLC receiver can accurately adjust and align the audio sample framing to ensure robust recovery of the audio sample stream.

In another embodiment, not part of the invention, audio clock synchronization between source and end-point can be accomplished through a PLC precision time protocol (PTP) update. The following description of this further embodiment will focus on the differences between it and the previously described embodiment. Therefore, features which are common to both embodiments will be omitted from the following description, and so it should be assumed that features of the previously described embodiment are or at least can be implemented in the further embodiment, unless the following description thereof requires otherwise.

In this embodiment, the end-point Ethernet receiver adjusts and re-timestamps the PTP packetized clock information based upon the symbol timing information known within the PLC receiver. This technique requires the end-point PLC to have accurate timing information for its inbound symbols, similar to the previously discussed embodiment.

<FIG> illustrates an end-point audio clock synchronization system using PTP updates, under some embodiments, not part of the invention. The approach of system <NUM> uses PTP packets <NUM> utilized by the IEEE1588 standard of the AES67 format. System <NUM> comprises a source circuit <NUM> with the audio source generating packetized Ethernet signals for transmission over conductor <NUM> to end-point <NUM> for playback through speaker <NUM>, as described above with respect to <FIG>. For this embodiment, source <NUM> transmits audio data in the form of PTP packets <NUM> to the down-stream endpoint <NUM>. The PLC receiver <NUM> maintains certain PTP timing data <NUM>. Using this information, the end-point receiver <NUM> adjusts and re-timestamps the PTP packetized clock information <NUM> based upon the symbol timing information known within the PLC receiver. The PTP timing data comprises accurate timing information for its inbound symbols. Said differently, the PLC receiver is configured to monitor timing of PLC encoded symbols to adjust and to re-timestamp the PTP packets.

The end-point PLC <NUM> measures and provides symbol latency and symbol-to-symbol jitter performance, and then adjusts and/or re-timestamp each PTP packet to accommodate for the PLC's time varying latency and jitter aspects. Once the PTP packets are adjusted to accommodate for PLC latency and jitter, the end-point Ethernet audio receiver <NUM> utilizes its existing PTP clock synchronization schemes to accurately synchronize the end-point clock to that of the source Ethernet audio transmitter <NUM>. For this embodiment, the PLC receiver <NUM> monitors symbol timing parameters that would be used by subsequent re-timing algorithms to correct the PTP packets as needed. Similar to the embodiment described above, the PLC receiver can monitor the symbol-to-symbol latency, delay, and nominal jitter performance of the physical layer (the loudspeaker cabling), the PLC receiver can pass this time skew information to the PTP algorithm, wherein the clock and audio frame recovery algorithms can be re-aligned to the transmitter. It should be noted that in this embodiment, the clock recovery scheme uses packet-based recovery (e.g., PTP), and then adjusts the recovered clock packets to achieve alignment and synchronization, in contrast to the embodiment described above, which uses the inherent PLC clock synchronization infrastructure to achieve synchronization. The master clock is the primary high frequency time-base that is used to maintain phase coherency between all digital devices within the system. The master clock may typically operate at a frequency of <NUM>-<NUM>. In audio systems the master clock may operate at a frequency multiple of the frequency of an audio sample. For example, if the the frequency of an audio sample rate is <NUM>, the master could operate at a frequency of <NUM>, which is <NUM> times the frequency of the audio sample. The PTP method described above can be regarded as a method of transmitting and recovering the audio sample clock over a time-variant physical layer (like Ethernet). The packetized data may incur varying delays as the packets move through a traditional time-variant physical layer, like Ethernet (i.e. through hubs/switches/routers). Typically, in conventional systems, the varying delays (and jitter) of a traditional Power-line Communication (PLC) physical layer cause that the PTP system is unable to recover the audio sample clock, and thus PTP transmission via a PLC physical layer doesn't work properly. In order to solve this problem, in the PTP method of this disclosure, the PLC physical layer devices (i.e. the PLC transmitter and the PLC receiver) are synchronized by the master clock and the PLC receiver monitors the latency and jitter of the inbound PLC encoded data (e.g. the PLC symbols being transmitted over the physical power line). After that the PLC receiver can utilize this timing information (e.g. the PLC symbol latency and jitter), to adjust the timing of the PTP packets and to re-timestamp them. This ensures that the PTP packets are properly clocked without gaps and drop outs such that an audio stream can be properly played back.

<FIG> is a flowchart that illustrates a method of providing end-point audio clock synchronization through a PLC PTP update, under some embodiments not part of the invention. As shown in <FIG>, process <NUM> begins with the end-point receiving the PLC signal from the source side, <NUM>. The end-point PLC receiver measures and provides symbol latency and symbol-to-symbol jitter performance using its internal clock recovery and symbol timing monitoring algorithms, <NUM>. A down-stream algorithm then adjusts or re-timestamps each PTP packet to accommodate for the PLC's time varying latency and jitter aspects, <NUM>. This algorithm would change the PTP packet time stamp to adjust for the symbol latency as measured over the nominal physical layer, and can be executed within the Ethernet audio receiver integrated circuit or programmable logic device. Once the PTP packets are adjusted to accommodate for PLC latency and jitter, the end-point Ethernet audio receiver utilizes its existing PTP clock synchronization schemes to accurately synchronize the end-point clock to that of the master (source) transmitter, <NUM>. This embodiment requires the PLC receiver in the end-point to monitor symbol timing parameters that would be used by subsequent re-timing algorithms to correct the PTP packets as needed.

This embodiment PLC PTP update embodiment may be used in conjunction with the master clock transmission/recovery/synchronization scheme described in <FIG>. Thus, the signal received in step <NUM> by the end-point may be the standard audio/power signal transmitted along conductor <NUM>, as shown in <FIG>, or it may be a master clocked signal as shown in <FIG>.

Embodiments may be used to playback any appropriate type of audio format including stereo, surround-sound, object-based audio, or spatial (immersive) audio content. An example immersive audio system and associated audio format is the Dolby Atmos platform. Such a system incorporates a height (up/down) dimension that may be implemented as a <NUM>, <NUM>, <NUM> surround system, or similar surround sound configuration (e.g., <NUM>, <NUM>, <NUM>, etc.). In general, these speakers may be used to produce sound that is designed to emanate from any position more or less accurately within the listening environment. Immersive audio can be used in a wide variety of venues including cinemas, auditoriums, homes, and so on. The end-point speakers may thus be placed in any appropriate location and distance from the audio source. Such speakers may also be implemented in any appropriate configuration, such as single or multi-way speakers, soundbars, standing or bookcase speakers, LFE (low-frequency effect) speakers, height speakers, and so on.

Embodiments can also be used in any appropriate power line (AC mains) infrastructure. In home applications, the direct amplification system may enable multi-channel audio distribution through a house without burdening Wi-Fi or other wireless infrastructures. Because most powered loudspeakers require some connection to AC mains, the reliable transmission of audio could be directly realized without additional audio signal wiring. Embodiments of the direct amplification audio system described herein may thus be used in any appropriate venue or application, such as cinema, home cinema, live venue, auditorium, industrial facility, military facility, theme park, and so on.

Although example implementations are described with respect to certain specified components, such as the Dolby Cinema Processor CP850, it should be noted that embodiments are not so limited and any similar or other appropriate component may be used.

Unless the context clearly requires otherwise, throughout the description and the claims, the words "comprise," "comprising," and the like are to be construed in an inclusive sense as opposed to an exclusive or exhaustive sense. Words using the singular or plural number also include the plural or singular number respectively. When the word "or" is used in reference to a list of two or more items, that word covers all of the following interpretations of the word: any of the items in the list, all of the items in the list and any combination of the items in the list.

Claim 1:
A distributed audio speaker system (<NUM>) comprising an audio source (<NUM>) and a plurality of end-points (<NUM>), each end-point of the plurality of end-points having a speaker (<NUM>) configured to playback the audio, an Ethernet receiver (<NUM>) coupled to the speaker, and a power line communication, PLC, receiver (<NUM>) coupled to the Ethernet receiver, wherein the audio source is configured to transmit the audio and the power over a common conductor (<NUM>) to the plurality of end-points, and wherein the audio source comprises
a power supply configured to generate the power,
a PLC transmitter (<NUM>) coupled to an output of the power supply,
an Ethernet audio transmitter (<NUM>) coupled to the PLC transmitter, and
a master clock (<NUM>) coupled to the PLC transmitter and the Ethernet audio transmitter, wherein the master clock is configured to generate a master clock signal for both the Ethernet audio transmitter and PLC transmitter, wherein the PLC transmitter is configured to generate a PLC encoded signal comprising the audio and to transmit the PLC encoded signal and the power over the common conductor, wherein an end-point of the plurality of endpoints is configured to receive the PLC encoded signal and the power, wherein the PLC receiver of the end-point is configured to recover the master clock signal from the PLC encoded signal to synchronize the Ethernet receiver of the end-point to the Ethernet transmitter of the audio source, wherein the PLC encoded signal comprises PLC telemetry information including PLC symbol latency and jitter, and wherein the end-point is configured to further adjust the recovered master clock signal to align with an audio sample stream of the transmitted PLC encoded signal using the telemetry information.