Interface for loudspeakers with digital input signals based on IEC 60958

IEC 62537:2010 specifies the requirements for a digital loudspeaker interface based on the IEC 60958 series of standards and the MIDI specification. It maximizes flexibility and value by combining these previously separate standards. Together, the two standards provide a simple and flexible digital interface for loudspeakers. This bilingual version, published in 2010-09, corresponds to the English version. The French version of this standard has not been voted upon.

Interface pour haut-parleurs avec signaux d'entrée numériques basés sur la CEI 60958

La CEI 62537:2010 spécifie les exigences d'une interface pour haut-parleurs numériques basée sur la série de normes CEI 60958 et sur la norme MIDI. Elle optimise la souplesse et la valeur en combinant ces normes qui étaient précédemment distinctes. Les deux normes fournissent ensemble une interface numérique simple et souple pour haut-parleurs. La présente version bilingue, publiée en 2010-09, correspond à la version anglaise. La version française de cette norme n'a pas été soumise au vote.

General Information

Status
Published
Publication Date
27-Jun-2010
Current Stage
PPUB - Publication issued
Start Date
28-Jun-2010
Completion Date
28-Jun-2010
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IEC 62537
Edition 1.0 2010-06
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
Interface for loudspeakers with digital input signals based on IEC 60958
Interface pour haut-parleurs avec signaux d’entrée numériques basés sur la
CEI 60958
IEC 62537:2010
---------------------- Page: 1 ----------------------
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---------------------- Page: 2 ----------------------
IEC 62537
Edition 1.0 2010-06
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
Interface for loudspeakers with digital input signals based on IEC 60958
Interface pour haut-parleurs avec signaux d’entrée numériques basés sur la
CEI 60958
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
PRICE CODE
INTERNATIONALE
CODE PRIX
ICS 33.160.30; 35.040 ISBN 978-2-88912-196-0
® Registered trademark of the International Electrotechnical Commission
Marque déposée de la Commission Electrotechnique Internationale
---------------------- Page: 3 ----------------------
– 2 – 62537 © IEC:2010
CONTENTS

FOREWORD...........................................................................................................................4

INTRODUCTION.....................................................................................................................6

1 Scope...............................................................................................................................7

2 Normative references .......................................................................................................7

3 Terms, definitions and abbreviations ................................................................................7

3.1 Terms and definitions ..............................................................................................7

3.2 Abbreviations ..........................................................................................................8

4 General ............................................................................................................................8

4.1 Feature set..............................................................................................................8

4.2 Audio formats ..........................................................................................................9

5 Control data channel using the U-bit of IEC 60958-4 ........................................................9

5.1 General ...................................................................................................................9

5.2 Formatting...............................................................................................................9

5.3 Mode indication .......................................................................................................9

5.4 Subchannel usage.................................................................................................10

6 Loudspeaker command set.............................................................................................10

6.1 General .................................................................................................................10

6.2 Device identification and configuration ..................................................................10

6.2.1 Device identification ..................................................................................10

6.2.2 Auto configuration .....................................................................................11

6.3 Parameters ...........................................................................................................11

6.3.1 Parameter identification.............................................................................11

6.3.2 Value range...............................................................................................11

6.3.3 Setting a parameter ...................................................................................12

6.3.4 Device addressing .....................................................................................12

6.3.5 Timed parameter setting (optional) ............................................................12

6.4 Optional alternative parameter setting through NRPN and/or MIDI controllers .......12

6.4.1 General .....................................................................................................12

6.4.2 NRPN and MIDI continuous controller association .....................................12

6.5 Control numbers....................................................................................................13

6.5.1 General .....................................................................................................13

6.5.2 MIDI channel assignment (control number 0, low resolution, optional) .......13

6.5.3 Volume (control number 1, high resolution, mandatory) .............................14

6.5.4 Volume ramp (control number 2, high resolution, optional) ........................14

6.5.5 Time delay (control number 3, high resolution, optional) ............................14

6.5.6 Sample delay (control number 4, high resolution, optional) ........................14

6.5.7 Volume calibration (control number 5, high resolution, optional) ................14

6.5.8 Panning (control number 6, high resolution, optional) ................................14

6.5.9 Phase left (control number 7, binary, optional)...........................................14

6.5.10 Phase right (control number 8, binary, optional).........................................15

6.5.11 Dimming (control number 9, binary, optional).............................................15

6.5.12 Indicator (control number 10, binary, optional)...........................................15

6.5.13 High-pass frequency (control number 11, high resolution, optional) ...........15

6.5.14 High-pass filter in/out (control number 12, binary, optional) .......................15

6.5.15 Low-pass frequency (control number 13, high resolution, optional) ............15

6.5.16 Low-pass filter in/out (control number 14, binary, optional) ........................15

---------------------- Page: 4 ----------------------
62537 © IEC:2010 – 3 –

6.6 Additional MIDI messages .....................................................................................15

6.6.1 General .....................................................................................................15

6.6.2 All off and restore commands (mandatory).................................................16

6.6.3 Program change (optional) ........................................................................16

7 Power transmission and backward channel (optional) .....................................................16

7.1 Power transmission ...............................................................................................16

7.2 Backwards data channel........................................................................................17

7.2.1 General .....................................................................................................17

7.2.2 Protocol.....................................................................................................17

7.2.3 Simultaneous reception .............................................................................17

Annex A (informative) Security aspects................................................................................18

Annex B (informative) Signal routing....................................................................................21

Annex C (informative) Application examples ........................................................................23

Annex D (informative) Implementation using current hardware.............................................25

Bibliography..........................................................................................................................26

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– 4 – 62537 © IEC:2010
INTERNATIONAL ELECTROTECHNICAL COMMISSION
_____________
INTERFACE FOR LOUDSPEAKERS WITH DIGITAL INPUT SIGNALS
BASED ON IEC 60958
FOREWORD

1) The International Electrotechnical Commission (IEC) is a worldwide organization for standardization comprising

all national electrotechnical committees (IEC National Committees). The object of IEC is to promote

international co-operation on all questions concerning standardization in the electrical and electronic fields. To

this end and in addition to other activities, IEC publishes International Standards, Technical Specifications,

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Publication(s)”). Their preparation is entrusted to technical committees; any IEC National Committee interested

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with the International Organization for Standardization (ISO) in accordance with conditions determined by

agreement between the two organizations.

2) The formal decisions or agreements of IEC on technical matters express, as nearly as possible, an international

consensus of opinion on the relevant subjects since each technical committee has representation from all

interested IEC National Committees.

3) IEC Publications have the form of recommendations for international use and are accepted by IEC National

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Publications is accurate, IEC cannot be held responsible for the way in which they are used or for any

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4) In order to promote international uniformity, IEC National Committees undertake to apply IEC Publications

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5) IEC itself does not provide any attestation of conformity. Independent certification bodies provide conformity

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8) Attention is drawn to the Normative references cited in this publication. Use of the referenced publications is

indispensable for the correct application of this publication.

9) Attention is drawn to the possibility that some of the elements of this IEC Publication may be the subject of

patent rights. IEC shall not be held responsible for identifying any or all such patent rights.

International Standard IEC 62537 has been prepared by technical area 4: Digital system

interfaces and protocols, of IEC technical committee 100: Audio, video and multimedia

systems and equipment.

This bilingual version, published in 2010-09, corresponds to the English version.

The text of this standard is based on the following documents:
CDV Report on voting
100/1433/CDV 100/1700/RVC

Full information on the voting for the approval of this standard can be found in the report on

voting indicated in the above table.
The French version of this standard has not been voted upon.

This publication has been drafted in accordance with the ISO/IEC Directives, Part 2.

---------------------- Page: 6 ----------------------
62537 © IEC:2010 – 5 –

The committee has decided that the contents of this publication will remain unchanged until

the stability date indicated on the IEC web site under "http://webstore.iec.ch" in the data

related to the specific publication. At this date, the publication will be
• reconfirmed,
• withdrawn,
• replaced by a revised edition, or
• amended.
---------------------- Page: 7 ----------------------
– 6 – 62537 © IEC:2010
INTRODUCTION

The IEC 60958 interface allows transmission of 2-channel digital audio with up to 24 bit word

length at 192 kHz sampling rate. This is adequate for loudspeakers, however, there are

additional needs in practice that require standardisation, which go beyond what is currently

defined in IEC 60958. This standard is aimed at fulfilling those needs.

IEC 60958 features a user bit that can form the basis of a control data channel that addresses

those additional requirements. The format of this user bit data channel is based on the

existing MIDI standard.

Beyond the needs given in IEC 60958, the following offers an exemplary, but incomplete list

of of what a digital loudspeaker interface should support:
• Remote control of operating parameters of the loudspeaker.

• Remote power-on of the loudspeaker – preferably without requiring standby power in

the loudspeaker.

• Remote configuration of loudspeaker, for example crossover configuration, or firmware

update.

• Remote supervision of loudspeakers, for example chassis temperature or amplifier

integrity.

• Remote identification of loudspeakers, to allow auto-configuration of the entire system.

• Control of individual or groups of loudspeakers through a single interface.
• Remote control of Audio System through remote control receiver mounted in
loudspeaker enclosure (allowing Audio System to be placed out of sight).
• Extensions to allow for future applications.

NOTE 1 Level and mute control in the loudspeaker is preferred over digital attenuation by the signal source, as

this allows the full audio data word length for the filter network; level should be controlled at the last stage in front

of power amplifiers. In this case, the advantage is that the full audio word length of the given format is available at

any time and at any volume setting. Especially, if a fully digitally constructed crossover network has been

implemented, more precise arithmetical operations can also be made at low volumes. Volume control can thus be

carried out after the crossover network or even after the relevant final amplifier. Even under the most unfavourable

conditions (digital pre-attenuation and analogue gain) the filters and controllers receive the full audio word width

under all operating conditions (ideal state).

NOTE 2 Not all of the listed features are required in all applications. It should therefore be up to the implementer

to select from this standard the parts that are required in his application, and omit the unnecessary features. See

Annex D for application examples.
---------------------- Page: 8 ----------------------
62537 © IEC:2010 – 7 –
INTERFACE FOR LOUDSPEAKERS WITH DIGITAL INPUT SIGNALS
BASED ON IEC 60958
1 Scope

This International Standard specifies the requirements for a digital loudspeaker interface

based on the IEC 60958 series of standards and the MIDI specification. It maximizes flexibility

and value by combining these previously separate standards. Together, the two standards

provide a simple and flexible digital interface for loudspeakers.

Examples for applications of the interface can be found in Annex C of this standard.

2 Normative references

The following referenced documents are indispensable for the application of this document.

For dated references, only the edition cited applies. For undated references, the latest edition

of the referenced document (including any amendments) applies.
IEC 60958 (all parts), Digital audio interface
IEC 60958-4, Digital audio interface – Part 4: Professional applications
The Complete MIDI 1.0 Detailed Specification v96.1:2001, (Second edition)
3 Terms, definitions and abbreviations
3.1 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
3.1.1
digitally interfaced loudspeaker

device that combines a loudspeaker with an amplifier, where the amplifier has a digital audio

input port

NOTE The amplifier and loudspeaker may share a common enclosure, or they may occupy separate enclosures.

The connection between amplifier and loudspeaker and the operating principle of the transducer are left

unspecified and may be analogue. In the context of this standard, the term may be abbreviated as loudspeaker or

speaker when there is no risk of confusion.
3.1.2
phantom power

scheme of transmitting electrical power from a source device to a target device using the

balanced wiring employed for data transfer; in particular, the power is applied between both

balanced signal wires and the ground or shield connection
3.1.3
audio data
data sent to the loudspeaker that is rendered as sound by the loudspeaker
NOTE Typically this data would be in PCM 2’s complement format.
---------------------- Page: 9 ----------------------
– 8 – 62537 © IEC:2010
3.1.4
control data
data sent to the loudspeaker that controls its operating parameters
3.1.5
controller
source device for control data
3.1.6
solid state relay
assembly of an optically controlled power switch and a LED
3.2 Abbreviations
AES Audio Engineering Society
ASIC Application Specific Integrated Circuit
CODEC Coder / Decoder
CPLD Complex Programmable Logic Device
CRC Cyclic Redundancy Check
DSP Digital Signal Processor
FPGA Field Programmable Gate Array
LED Light Emitting Diode
LSB Least Significant Bit
MIDI Musical Instrument Digital Interface
MSB Most Significant Bit
MSC MIDI Show Control
MTC MIDI Time Code
NRPN Non Registered Parameter Number
PCM Pulse Code Modulation
Sysex System-exclusive
4 General
4.1 Feature set

A digitally interfaced loudspeaker conforming to this standard shall implement the following.

• A control data channel from the controller to the loudspeaker which supports
transmission of MIDI messages. This may be implemented using the U-bit embedded
in the IEC 60958-4 protocol as described in Clause 5.
• A command set as described in Clause 6. A basic command set is mandatory, with
optional commands and manufacturer extensions being supported at the
manufacturer’s discretion.

• Optional: Power transmission from a controller to the loudspeaker, in order to activate

the loudspeaker's power switch. It is sufficient to transmit the power to operate a LED.

The power switch in the loudspeaker may be implemented with a solid state relay. A

phantom supply scheme is used, which employs the balanced interface wiring defined

in IEC 60958-4, see 7.1.

• Optional: A backwards data channel from the loudspeaker to the controller. As this

runs opposite to the signal flow on the IEC 60958 interface, it is implemented as a data

channel riding on the phantom power mentioned above, see 7.2.
---------------------- Page: 10 ----------------------
62537 © IEC:2010 – 9 –
4.2 Audio formats

As a configuration setting, the loudspeaker may select from the two subchannels. A mono

loudspeaker shall use the left channel audio data by default, but may optionally be configured

to use the right channel audio data in a manufacturer defined way.

NOTE 1 An optional parameter specifies panning between left and right channels. Speakers that implement this

feature can render an arbitrary mix of the two subchannels.

It is the manufacturer's decision which audio sampling frequencies to support, and whether

single channel double sampling frequency mode is supported. It is highly recommended that

48 kHz two-channel mode with no emphasis be amongst the supported formats.
NOTE 2 The manufacturer should document clearly which formats are supported.
5 Control data channel using the U-bit of IEC 60958-4
5.1 General

In the IEC 60958 interface there is a U-bit for each of the two subchannels, these form two

separate control data channels with a capacity of one bit per sample each.

NOTE Using both together to form a single data channel with twice the capacity would be possible but unwise in

the presence of signal routers, hence the two U-bit channels are kept separate, except when single channel double

frequency mode is used.
5.2 Formatting

The U-channel shall carry data formatted according to the MIDI standard, with the bits being

transmitted in inverted state. That is, a MIDI 1-bit is transmitted as a zero U-bit, and a MIDI

0-bit is transmitted as a one U-bit. This inversion ensures that an unused U-channel (which

carries 0-bits by default) is interpreted by the receiver as an idle line. For each information

byte, 10 bits are transmitted in the usual asynchronous frame format. The 8 data bits of a byte

are framed by a start bit and a stop bit.

NOTE 1 This allows the receiver to detect the start of each byte, and it also allows the transmitter to insert an

arbitrary number of idle bits between each data byte to adjust the bandwidth used.

NOTE 2 If the bits were transmitted in the non-inverted state, an idle U-channel would be seen by the MIDI

receiver as a line with a continuous break condition, which is a sequence of framing errors.

NOTE 3 As the U-bit is transmitted in lockstep with the audio data, it is possible to maintain a defined and sample

accurate reaction time between control data and audio data. One MIDI byte can be transmitted for every 10 sample

periods. Through insertion of idle bits, it is theoretically possible to position MIDI messages in a sample accurate

way.
5.3 Mode indication

The channel status bits shall indicate that the U-channel is carrying MIDI formatted data. The

binary value 0110 in the channel status of the respective subchannel (byte 1, bits 4 to 7) is

used to indicate this usage of the U-bit. This value is currently reserved.

NOTE The necessary amendments need to be added to IEC 60958-4. The amendment does not need to mention

any particular application, such as speakers. The definition allows the transmission of MIDI data for any purpose.

MIDI is a good match with IEC 60958 for several reasons: MIDI is an open-loop protocol that does not need a

backwards channel, although it can take advantage of one, should it be available. The data rate of MIDI is within

the same ballpark as the U-bit data rate in the IEC 60958 series. And MIDI is a general control protocol with a lot

of flexibility for custom extensions, and a lot of support in the industry, for example in the form of hardware and

software products. There are also various ways in which MIDI data can be transported in other interface standards,

such as IEEE 1394, USB or other computer networks.
---------------------- Page: 11 ----------------------
– 10 – 62537 © IEC:2010
5.4 Subchannel usage

A receiver shall listen to the U-bit channel corresponding to the audio channel it is rendering.

By default this would be the left subchannel. A loudspeaker rendering a mix of both

subchannels shall listen to the U-bit data on the left channel. Transmitters would preferably

send identical data on both U-bit channels, but this is not required.

If the IEC 60958 interface is in single channel double frequency mode, the U-bit channels of

both subframes shall also be combined into one logical data channel, mirroring the situation

for the audio data.
6 Loudspeaker command set
6.1 General

The command set is based on MIDI show control (MSC) commands as defined in the MIDI

standard. Device operating parameters are set using the MSC SET command.

NOTE 1 Since there is no mandatory backwards data channel, the command set avoids backwards

communication from speaker to controller as much as possible. The MIDI protocol shares the same open-loop

philosophy, making it a good candidate for a base protocol.

NOTE 2 MIDI distinguishes between up to 16 devices. MIDI sysex messages, however, do not have this

restriction and can address any number of devices. For example, MIDI Show Control (MSC) can address up to 112

distinct devices and 15 device groups.

NOTE 3 MIDI allows for vendor specific communication through sysex messages, which can be exploited by

individual companies for their own purposes, such as custom features or firmware downloading.

NOTE 4 Attention is drawn to the various features already defined within the MIDI standard, such as MIDI file

dump, which may be beneficial for speaker applications.

A loudspeaker shall support a way of receiving MIDI data. For example, this can be a

standard MIDI port, or an IEC 60958-4 port with MIDI embedded in the U-bit, as described in

Clause 5, or it can be MIDI embedded in a different transport, such as audio or data networks.

NOTE 5 It is strongly recommended to implement speakers in such a way that they are able to accept commands

at any time. Introduction of a dead time after reception of a command greatly complicates the job of a controlling

device. Also, it is practically impossible to define a dead time that suits every application.

NOTE 6 The command set described here is independent of the hardware interface used. Implem

...

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