IEC 62537:2010 pdf – Interface for loudspeakers with digital input signals based on IEC 60958.
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 I An optional parameter specifies panning between left and right channels. Speakers that implement this featur, can render an arbitrary mix of th, two
II 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 o4 signal routers, the two U-bit channels are kept separate, except when single channel double frequency mode I. used.
5.2 Formatting
The U-channel shaft 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 del.ct th. start of each byte, and ii also aliows the tranarnitler to insert an arbitrary number of idle bits between each data byte to adpust the bandwidth used.
NOTE 2 II the bits were transmitled in the noninverted state, an idle u-channel would be seen by the MID1 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 lime between control data and audio data. One MlDi byte can be transmitted for every 10 sample periods. Through insertion of idle bits. ills 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 i5 currently reserved.
NOTE The necessary amendments need to be added to IEC 80958-4 The amendment does not need to mention any particular application, such as speakers The definition allows the transmission of MlOl data for any purpose MIDI is a good match with IEC 80958 for several reasons: MIDI is ogen.loop prolocol 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 1EC 60958 series. And MIDI is a general control protocol with 1 101 of flexibility for custom extensions, and a lot of support In the industry, for example In tile lorm of hardware and software products. There are also various ways in which MIDI data can be transported in other interface atandarda SUCh as IEEE 1394. USB or other computer networks.