JP2007267030A - Audio network system having output delay correction function - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a delay correction technology for outputting acoustic signals from all nodes without any phase difference by considering a delicate delay such as a delay in a transmission line, also when transmitting audio sample data while circulating a packet in an annular audio network system. <P>SOLUTION: In the annular audio network system, frame data are transmitted by one packet from a master at each sampling period regularly with one of a plurality of nodes and other nodes as a master and slaves, respectively, and there is a region in which the sample data of a plurality of channels for the transmission between the nodes enter the packet. A time from a point in time when the packet is received to a point in time when a master node receives the packet is calculated as a correction time. When the sample data are outputted from each node to external equipment, an output time is delayed only by the correction time. <P>COPYRIGHT: (C)2008,JPO&amp;INPIT

Description

  The present invention relates to a technique for correcting even a phase difference in all nodes by correcting a time at which an acoustic signal is output from a node in consideration of a transmission delay time in a ring audio network system.

  Conventionally, CobraNet (registered trademark) described in Non-Patent Document 1 and Non-Patent Document as a technology for performing acoustic signal communication in audio network systems used for PA, music production, private broadcasting, etc. for concerts and plays, etc. 2. SuperMAC (registered trademark) described in No. 2 and EtherSound (registered trademark) described in Non-Patent Document 3 are known. These are techniques for transmitting acoustic signals over Ethernet (registered trademark).

On the other hand, a ring type transmission network such as FDDI / TokenRing is known as a technique used for a network for a telephone line. In this method, a token (data transmission right) circulates between nodes connected in a ring shape, and only the node that obtained the token can execute data transmission.
http://www.balcom.co.jp/cobranet.htm http://www.sonyoxford.co.uk/pub/supermac/ http://www.ethersound.com/news/getnews.php?enews_key=101

  As a transmission method of the acoustic signal (audio sample data), it is conceivable to use the above-described conventionally known ring type transmission network. FIG. 13 shows an example of a ring type audio network system. The signal circulates in a reciprocating manner such as node 1301 → node 1302 → node 1303 → node 1302 → node 1301. FIG. 14 also shows another example of a similar ring-type audio network system. In this example, the nodes 1401 to 1406 are physically connected in this order in a ring shape. The packet transmitted from the master node 1401 circulates once in one sampling cycle, such as node 1401 → node 1402 → node 1403 → node 1404 → node 1405 → node 1406. In this packet, a storage area for audio sample data of a plurality of channels (ch) is secured, and each node transmits data on necessary channels as appropriate.

  However, in such a system that transmits data in a ring shape, it is difficult to accurately match the output timings of the acoustic signals at all nodes. In particular, as long as a transmission line is used, there is a delay in signal transmission through that transmission line, and there is also a delay due to processing at each node. However, such a small delay is usually of little concern. is there. However, in various professional audio devices, such a slight delay is not allowed, and there is a case where it is desired to eliminate even the phase difference of the acoustic signals output from all nodes. For example, in order to strictly design / install a line array speaker system, it may be necessary to consider such a minute time.

  When transmitting audio sample data while circulating packets in a ring-type audio network system, the present invention takes into account a minute delay such as a delay in a transmission line, and an acoustic signal is transmitted from all nodes without any phase difference. An object of the present invention is to provide a delay correction technique that can be output.

  In order to achieve the above object, the present invention connects a plurality of nodes in a ring shape so that loop transmission is possible, and performs data transmission in one direction between the plurality of nodes to perform communication between arbitrary nodes. In the audio network system that performs the above, only one of the plurality of nodes is set as a master node, and the other nodes are set as slave nodes, and frame data is regularly transmitted from the master node packet by packet at each sampling period. In a system in which a round is taken during the sampling period, and in the packet, an area for storing audio sample data of a plurality of channels is provided for transmitting audio sample data between nodes. For each node, the master node receives the packet from the time the packet is received by the node. The time until the point in time is calculated as a correction time, and when audio sample data is output from each node to an external device, the output time is delayed by the correction time and output. is there.

  In particular, an arbitrary number of slave nodes are connected in a chain in the forward direction so that data can be transmitted in the forward direction from the master node. When the slave node reaches the terminal slave in the forward direction, the data is looped back at the slave node. Slave nodes are connected in a chain in the reverse direction so that data can be sent in the reverse direction from the slave node at the end of the direction to the master node, and any number of slave nodes can be connected so that data can be sent in the reverse direction from the master node. When the slave node is connected in a chain in the reverse direction and reaches the slave node at the end in the reverse direction, the slave node wraps the data and sends the data in the forward direction from the slave node at the reverse end to the master node. It is connected in a chain in the forward direction and constitutes a ring network by the connection relationship of such nodes. Then, in the master node, the delay time of the entire network until it circulates around the ring network and returns, the forward delay time until the packet is transmitted in the forward direction and returns from the reverse direction, The backward delay time from when the packet is transmitted in the reverse direction until it returns from the forward direction is obtained, and at each slave node, the reception time of the packet sent from the forward direction and the packet sent from the reverse direction A means for relatively calculating the difference is provided, and from these pieces of information, each node uses the time from when the packet is received at its own node to the time when the packet is received at the master node as a correction time. Try to calculate. When outputting audio sample data from each node, the output time is delayed by the correction time and output.

  According to the present invention, even in an audio network having a transmission delay, an acoustic signal can be output from each node at the same time, and an acoustic signal having the same phase can be output from all nodes. This is suitable for application to an audio system that strictly considers even the phase difference of the sound output of each node, such as a line array speaker system.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 shows a module configuration of an audio network system according to the present invention. The nodes 101 to 104 are four nodes connected so that the packet 150 circulates in a ring shape as indicated by a dotted line 151. A microphone 112 is connected to the node 101 via an analog-digital converter (ADC) 111. The node 101 can transmit audio data input via the ADC 111 to another node using an arbitrary channel of the circulating packet 150. A mixer 121 is connected to the node 102. The node 102 can capture audio data from an arbitrary channel of the circulating packet 150 and send it to the mixer 121. The mixer 121 executes various signal processing such as mixing processing of input audio data, volume level control processing, and effect applying processing. The audio data resulting from the signal processing is input from the mixer 121 to the node 102, and the node 102 can transmit the input audio data to another node using an arbitrary channel of the circulating packet 150. A power amplifier 132 and a speaker 133 are connected to the node 103 via a digital / analog converter (DAC) 131. Similarly, a power amplifier 142 and a speaker 143 are connected to the node 104 via the DAC 141. The node 103 can take in audio data from an arbitrary channel of the circulating packet 150, send it to the power amplifier 132 via the DAC 131, and emit sound from the speaker 133. The same applies to the node 104.

  Each of the nodes 101 to 104 includes a two-stage buffer of buffers A and B. Each buffer is a buffer for storing audio data to be captured by the node, and has a two-stage configuration in order to store the latest sample data and the sample data one sampling time ago for each channel. is there. The latest captured data is stored in a buffer (for example, 110A) with a symbol A, and a sample one sampling time before is stored in a buffer (for example, 110B) with a symbol B.

  FIG. 2 shows the hardware configuration of each node. One node includes a central processing unit (CPU) 201, a random access memory (RAM) 202, a read only memory (ROM) 203, a communication interface (I / F) 204, an audio I / O (input / output interface) 206, and A communication bus 208 is provided.

  The CPU 201 is a processing device that controls the overall operation of this node. The RAM 202 is a volatile memory used as a work area for setting a load area for programs executed by the CPU 201 and various buffers. The ROM 203 is a non-volatile memory that stores various programs executed by the CPU 201 and constant data. Another node 205 is connected to the communication I / F 204 as an external device. Although the other node 205 is shown as one block here, for example, if the node 102 is connected to both the nodes 103 and 101, a plurality of communication I / Fs 204 can be connected to these nodes. Is provided. The audio I / O 206 is an interface connected to an external device such as an ADC, a DAC, or a mixer.

  Here, a method of correcting the sample deviation in the audio network system of the present embodiment will be described. FIG. 8 is a diagram for explaining a sample deviation correction method. Nodes A to D are connected in a ring shape so that signals reciprocate, and node B is a master node. The master node B transmits a packet at the start timing of one sampling time. Node A stores data in ch1 of the packet to be circulated, node B stores data in ch2, node C stores data in ch3, and node D stores data in ch4. . Each node A to D captures all data of ch1 to ch4. Data 801 returns to the master node B at a certain sampling time t−1, and data of each channel at the sampling time t−1 is set. When the new sampling time t is entered, the node B stores the data of the time t in the ch2 area of the packet and transmits it to the next node C as the packet 802. Node C receives this as packet 803, stores the data at time t in the area of ch 3, and transmits it as packet 804 to the next node D. The node D receives this as a packet 805, stores data at time t in the area of ch4, and transmits it as a packet 806 to the return path. Nodes C and B on the return path simply pass the packet through (through) as shown in 807 and 808. The next node A receives this as a packet 809, stores data at time t in the area of ch1, and transmits it to the next node B as a packet 810. The master node B receives this as a packet 811 and waits until the next sampling time again, and then performs the same processing.

  Each node includes buffers A and B as described with reference to FIG. For example, in the case of the master node B, one row indicated by 822A is a buffer A for storing the latest sample data of each channel, and one row indicated by 822B is a buffer for storing sample data by one sampling time before each channel. B. The same applies to the other nodes. Each of the nodes A to D stores the data of ch1 to ch4 of the transmission packet in the buffer A when transmitting the packet to the next node. At this time, the data stored in the buffer A so far is copied to the buffer B, and then the data is stored in the buffer A. As a result, in each of the nodes A to D, the sample one sampling time before and the latest sample are always held in the buffer for each of ch1 to ch4.

  Each of the nodes A to D outputs the sample data stored in the buffers A and B so as not to cause a sample shift (output from the node, for example, pass to a mixer or emit sound through an amplifier). . For this purpose, the ch written in the node upstream from the self node (from the master node to the node immediately before the self node) along the data flow flowing through each node in a ring shape is stored in the buffer B 1 The data before the sampling time is output, and the data of the current sampling time stored in the buffer A for the channel written in the downstream node (from the node immediately after the own node to the node immediately before the master node) is output. Output. For the channel to be written by the own node, in the example of FIG. 8, since the data of the current sampling time to be written is stored in the corresponding channel of the packet and then written to the buffer A together with the data of the other channels, channel data is output. (Of course, since the received packet may be stored in the buffer and then the data of the channel to be written in the own node may be updated, when processing in such a procedure, it may be output from the buffer A.) Each sample with an ellipse indicates a sample output from each node in accordance with the rules described above. As a result, the samples at time t−1 can be output all at once without shifting the samples.

  It is assumed that information on the connection position of each node and which channel is written in each node is shared in advance among all nodes. For example, when this system is started up, when the node configuration is changed, or when the channel to be written to the packet at each node or the channel to be fetched from the packet is changed, for example, the control data is transferred between the nodes at the initiative of the master node. It is only necessary to share these information by exchanging with each other.

  FIG. 3 is a flowchart of an audio data input routine executed at a node when a packet that goes around each node is received. In step 301, audio data of channels to be input at this node is input. This means that, for example, the acoustic signal from the microphone 112 is input via the ADC 111 at the node 101 in FIG. 1 or the digital acoustic signal output from the mixer 121 is input to the node 102. In step 302, the data of the channel in the received packet is overwritten and updated with the latest sample input in step 301. In step 303, the data of the channel in buffer B storing the sample of the previous sampling time (cycle) is discarded. In step 304, the data of the corresponding channel in the buffer B is overwritten with the data of the corresponding channel in the buffer A in which the sample for the current cycle is stored. In step 305, the data of the channel in buffer A is overwritten with the data of the channel in the packet. When inputting a plurality of channels, the above process may be repeated. Note that the discarding of the data in step 303 is automatically discarded by overwriting in step 304.

  FIG. 4 is a flowchart of an audio data output routine for outputting sample data taken into the buffer at each node to an external device. This means that, for example, sample data is output from the node 102 in FIG. 1 to the mixer 121, or sound is emitted from the nodes 103 and 104 via the DAC and amplifier. In step 401, it is determined whether the output data of all channels to be output to the outside has been updated at this node. This is a process for determining whether all the sample data of the channels to be output are collected in a predetermined work area (output data). If not, in step 402, the position information of the node storing the sample of the corresponding channel in the packet is acquired. In step 403, it is determined whether the node position is before the own node (from the master node to the node immediately before the own node) or after the node (from the node immediately after the own node to the node immediately before the master node). If it is the preceding node, in step 404, the sample data of the corresponding channel is obtained from the buffer B for the previous cycle. If it is the latter stage, in step 405, the sample data of the corresponding channel is obtained from the buffer A for the current cycle. In step 406, the output data is updated with the acquired data, and the process returns to step 401. When the sample data for all the channels to be output are obtained as output data, the process proceeds from step 401 to step 407, and audio data output time correction processing (described in detail later) is performed. Next, in step 408, the audio data of the channel to be output at this node is output to the designated external device.

  As described above, the sample deviation correction described with reference to FIG. 8 is performed, and samples having the same sampling time are simultaneously output from the respective nodes.

  In FIG. 8, the buffer has a two-stage configuration, but the buffer has an n + 1 (n is an integer of 1 or more) stage configuration, and n + 1 number of samples from a sample read in the current sampling period to a sample read out before n sampling periods. Audio sample data is stored, and at the time of output, if the node that puts the sample in the packet is upstream from its own node, the sample before n sampling periods is read and output, and if it is downstream from its own node The sample before the n-1 sampling period may be read and output.

  Next, the audio data output time correction process in step 407 will be described in detail. By correcting the sample deviation, the output timing can be adjusted in units of samples. However, since the sample data of each channel is transmitted by putting data on a packet that circulates in the ring-shaped network described above, a delay due to a transmission path between nodes occurs. This delay is small and can be ignored, but such a small delay may not be allowed in professional audio equipment. The audio data output time correction process is a process of correcting the delay caused by such a transmission path and matching the output timing of the audio signal output from each node with high accuracy.

The audio data output time correction process will be specifically described. Here, description will be made on the assumption of a network having a connection form in which signals reciprocate as shown in FIG. The writing of data into the packet and the capturing of data from the packet at each node are performed in the forward route, and the return route only passes through the packet. First, for explanation, as shown in FIG. 9, the delay time in the wiring length a is t (a), the transmission / reception time on the forward side for each node 901, 902 is T _FT , T _FR , backward side The transmission / reception times are denoted as T _BT and T _BR , respectively. Also, the delay time of the entire network is Total Delay, the delay time of the forward / backward side starting from the master node is Forward Delay, Backward Delay, and the packet reception time difference at each node is Node (Name) Delay, respectively write. Total Delay is a delay time when the network is visited once. Forward Delay is a delay time until data transmitted from the forward side of the master node returns and is received on the forward side. Backward Delay is a delay time until data transmitted from the backward side of the master node returns and is received on the backward side.

  The direction in which the master node starts packet transmission at the start timing of the sampling period is called “forward side”, and the opposite direction is called “backward side”. In FIG. 9, the right side of the figure is the forward side, and the left side is the backward side (the same applies to FIGS. 10 and 11).

  FIG. 10 shows the delay time calculated in the master node. FIG. 10A shows an example in which the master node 1001 is arranged at the end on the backward side, and the backward side output of the master node 1001 is directly connected to the backward side input in the master node. In FIG. 10B, the master node 1012 is between the slave nodes 1011 and 1013, and the slave nodes 1011 and 1013 are connected to the forward-side input / output and the backward-side input / output of the master node 1012, respectively. It is an example. FIG. 10C shows an example in which the master node 1023 is arranged at the forward end, and the forward output of the master node 1001 is directly connected to the forward input in the master node. For each of these examples, Total Delay, Forward Delay, and Backward Delay are calculated as shown in the figure. Here, the case where there are three nodes is taken as an example, but the calculation may be similarly performed when more nodes are connected.

FIG. 11 shows a delay time calculated in the slave node. Each slave node calculates a reception time difference (delay time) between forward and backward packet data. The calculation method of this delay time differs depending on the positional relationship with the master node. For example, as shown in FIG. 11 (a), in slave nodes 1102 and 1103 (named S3 and S4, respectively) on the forward side with respect to the master node 1101, FIGS. 11 (d) and 11 (e) As shown in FIG. 4, the delay time is calculated by T _FR −T _BR . On the other hand, in the slave nodes 1104 and 1105 (named S1 and S2 respectively) on the backward side with respect to the master node 1101, as shown in FIGS. 11B and 11C, T _BR −T Calculate the above delay time with _FR . In the connection example of FIG. 11A, the delay time calculated by the master node 1101 is as shown in FIG.

  FIG. 12 shows a calculation example of the correction time for how much the output time is delayed when sample data is output to an external device (such as a mixer or an amplifier) at each node. In FIG. 12A, the horizontal axis indicates the direction of passage of time, and S1, S2, M, S3, and S4 arranged on the vertical axis indicate the master node and the slave node in FIG. The arrows of M → S3 → S4 → S3 → M → S2 → S1 → S2 → M indicate that the packet data circulates in accordance with this arrow in the network configuration of FIG. The arrow indicates the forward path, and the arrow pointing upward to the right indicates the return path.) When the packet data circulates according to this arrow, the delay time between the nodes is indicated by 1204. Reference numeral 1201 denotes a total delay, 1202 denotes a forward delay, and 1203 denotes a backward delay.

  1213 in FIG. 12A indicates the timing at which the packet transmitted from the master node M is received by the slave node S3. Upon reception of this packet, the processing of FIG. 4 described above is executed in the node S3. Similarly, the processing of FIG. 4 is executed at the node S4 at the timing 1214, the node S1 at the timing 1211, and the node S2 at the timing 1212. If the output time correction in step 407 is not performed in the processing of FIG. 4 at each node, the node S3 outputs audio data at timing 1213, the node S4 outputs audio data at timing 1214, and so on. Since processing is performed, the output timing is shifted at each node. Therefore, in the present embodiment, the timings 1213, 1214, 1211 and 1212 at each node are delayed to the timing 1210, respectively. Timing 1210 is timing when the packet returns to the master node. By waiting until this timing 1210, samples of the same sampling time are prepared in all the nodes, and output at the same time makes it possible to match the output timing of the audio signal with high accuracy. The delay time from the packet reception timing to the timing 1210 at each node is called a correction time. Reference numerals 1221 to 1224 denote a calculation method of the correction time at each node.

FIG. 12B shows a calculation method of the correction time for the slave node on the forward side. The forward-side slave nodes are, for example, nodes S3 and S4. In short, these nodes only need to calculate the time from when a packet is input to the backward input (T _BR ) of the own node until the packet returns to the master node. − {(Total Delay) − (Backward Delay) − (Node (Name) Delay)} / 2 This is rearranged to obtain the equation of FIG. Expressions 1223 and 1224 are obtained by substituting FIG. 11F into the expression of FIG.

FIG. 12C shows a method of calculating the correction time for the slave node on the backward side. The slave nodes on the backward side are, for example, nodes S1 and S2. In short, in these nodes, it is only necessary to calculate the time from when a packet is input to the backward input (T _BR ) of the own node until the packet returns to the master node. Total Delay)-(Forward Delay)-(Node (Name) Delay)} / 2. This is the equation of FIG. Expressions 1221 and 1222 are obtained by substituting FIG. 11F into the expression of FIG.

  FIG. 5 is a flowchart of the master node delay time calculation routine. In step 501, a delay time (Total Delay) of the entire network is calculated. In step 502, a forward delay time is calculated. In step 503, a backward delay time (Backward Delay) is calculated. In step 504, the information is notified to all nodes. Through the above processing, each delay time described in FIG. 10 is calculated.

  FIG. 6 is a flowchart of a slave node delay time calculation routine. In step 601, delay time information (Total Delay, Forward Delay, Backward Delay) on the entire network, forward side, and backward side is acquired. In step 602, it is determined whether the position of the own node is the forward side or the backward side. If it is the forward side, the packet time reception difference of its own node is obtained in step 603, and the correction time is calculated by the formula shown in FIG. 12B in step 604. On the backward side, the packet time reception difference of the own node is obtained in step 605, and the correction time is calculated by the equation shown in FIG.

  The delay times described in FIGS. 10 and 11 are calculated by the processes in FIGS. The processing in FIGS. 5 and 6 is executed in advance before starting transmission of audio data, and the correction time is calculated in each slave node.

  FIG. 7 is a flowchart of an audio data output routine of the slave node. This process is executed in step 407 of FIG. In step 701, the timer is reset, and in steps 702 and 703, the timer waits until the correction time (which is calculated in step 604 or 606 above in this node) is exceeded. Return if the correction time is exceeded. After that, since audio data is output in step 408 of FIG. 4, the output is delayed by the correction time for each node as described with reference to FIG.

  In the above embodiment, the connection-related audio network system as shown in FIG. 13 has been described as an example. However, any audio network system that connects a plurality of nodes in a ring shape and circulates packets can be used. The present invention can also be applied to any device. In that case, in each node, the time from when the packet is received at the node to the time when the packet is received at the master node may be obtained and used as the correction time. When the system is started up, a correction time measurement packet is sent, and thereby the time from when the packet is received at each node to when the packet is received at the master node may be obtained.

Module configuration diagram of an audio network system according to the present invention Hardware configuration diagram of each node Audio data input routine flowchart Audio data output routine flowchart Flowchart of master node delay time calculation routine Flow chart of slave node delay time calculation routine Flowchart of slave node audio data output routine Diagram for explaining sample deviation correction method Diagram showing the definition of delay time and transmission / reception time Diagram showing the delay time calculated on the master node Diagram showing delay time calculated in slave node The figure which shows the calculation example of the correction time in each node Diagram showing an example of a ring-type audio network system Diagram showing another example of ring-type audio network system

Explanation of symbols

  DESCRIPTION OF SYMBOLS 101-104 ... Node, 150 ... Packet, 111 ... Analog-digital converter (ADC), 112 ... Microphone, 121 ... Mixer, 131, 141 ... Digital-analog converter (DAC), 132, 142 ... Power amplifier, 133, 143 … Speaker.

Claims (2)

An audio network system in which a plurality of nodes are connected in a ring shape so that loop transmission is possible, data transmission is performed in one direction between the plurality of nodes, and communication between arbitrary nodes is performed,
Only one of the plurality of nodes is a master node, the other nodes are slave nodes,
In these nodes, an arbitrary number of slave nodes are connected in a chain in the forward direction so that data can be sent in the forward direction from the master node. The slave nodes are connected in a chain in the reverse direction so that data is sent in the reverse direction from the slave node at the end in the forward direction to the master node, and further, the data is sent in the reverse direction from the master node. Any number of slave nodes are connected in a chain in the reverse direction. When the slave node reaches the end slave node in the reverse direction, the data is looped back at the slave node, and forward from the slave node at the reverse end to the master node. The slave nodes are connected in a chain in the forward direction so that data can be sent to them, and the connection relationship of such nodes It constitutes a more ring network,
At each sampling period, the master node regularly transmits frame data one packet at a time, and during the sampling period, the packet is transmitted so as to make a round of a plurality of nodes connected in the ring shape,
In the packet, an area for storing audio sample data of a plurality of channels is prepared,
The master node is
A delay time of the entire network until the packet circulates around the ring network and returns; a forward delay time until the packet is transmitted in the forward direction and returns from the reverse direction; and Means for obtaining the backward delay time from the transmission in the reverse direction to the return from the forward direction;
Means for notifying all the slave nodes of the obtained delay time of the entire network, forward delay time, and backward delay time;
Each slave node is
Means for relatively calculating a difference between reception times of a packet sent from the forward direction and a packet sent from the reverse direction;
Using the difference between the calculated reception times and the information notified from the master node, the time from when the packet is received at the own node to the time when the packet is received at the master node is calculated as the correction time. Means to
Means for reading audio sample data of the channel to be read by the own node from the packet;
Storage means for storing audio sample data of the read channel;
An audio network system comprising: means for outputting an output time of the audio sample data stored in the storage means with a delay by the correction time. An audio network system in which a plurality of nodes are connected in a ring shape so that loop transmission is possible, data transmission is performed in one direction between the plurality of nodes, and communication between arbitrary nodes is performed,
Only one of the plurality of nodes is a master node, the other nodes are slave nodes,
At each sampling period, the master node regularly transmits frame data one packet at a time, and during the sampling period, the packet is transmitted so as to make a round of a plurality of nodes connected in the ring shape,
In the packet, an area for storing audio sample data of a plurality of channels for transmitting audio sample data between nodes is prepared,
For each node, the time from when the packet is received at the node to the time when the packet is received at the master node is calculated as a correction time,
When outputting audio sample data from each of the nodes to an external device, the output time is delayed by the correction time and output.

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