EXAMPLE 1: If a transmission network only comprises DRM robustness mode E and FM transmissions, the DRM transmission can be broadcast without any additional delay (defining the new common reference t0), while the required delay for the analogue FM broadcast is d6-d2 = 950 ms.

EXAMPLE 2: If a transmission network only comprises DRM robustness modes A, B, C and D (short interleaver), DAB+, and AM transmissions, the DRM transmission can be broadcast without any additional delay (defining the new common reference t0). The required broadcast delay for the

DAB+ transmission in this case is d4-d1 = 850 ms, the delay for the analogue AM signal is d6-d1 = 1 400 ms.

R.4 Receiver implementation rules

It is the responsibility of each receiver implementation to internally align and co-time the decoded audio signal for each reception path and for each signal configuration, based on the well-defined transmission delays of the audio content carried in the signal-on-air as well as any receiver specific decoding and processing steps.

There are additional measures available for receiver implementations to support the listener experience of seamless switching of audio signals from different broadcast systems:

•If a receiver needs to switch between two alternative sources for the same audio programme, it should perform a time limited cross-fading between the two audio signals. This prevents annoying interruptions of the audio signal and covers minimal timing differences between those two sources.

•Alternatively a receiver might calculate the correlation of the decoded audio signals and adjust its internal delay values accordingly. In this case even a direct switch between audio sources should feel seamless.

•In addition the receiver could adjust the audio loudness level of the different sources if possible to support the impression of seamless source switching.

R.5 Definition of broadcast signal time references

The following definitions are used as broadcast system specific time references to align the broadcast delays of the signals-on-air. These time references are shown in figure R.2. All of the following definitions refer to the transmission of a particular part of the programme's audio content labelled "A".

NOTE: This definition of broadcast time references does not intend to result in a highly precise broadcast signal alignment as it would for example be required for SFN operation (single frequency networks). Instead these definitions should be seen as reference points that should be targeted by the broadcaster as precisely as technically possible, e.g. by fine-tuning the input delays of audio sources before feeding them into the respective broadcast encoder.

For analogue AM or FM broadcasts, the broadcast time shown in figure R.2 refers to the very moment when the audio signal "A" is put on air as part of the AM or FM coded transmission signal, respectively.

For DRM broadcasts the indicated broadcast time refers to the start of the transmission frame containing the audio super frame (in case of robustness mode E, the first part of the audio super frame) that carries the audio signal "A" as the first audio samples encoded into that audio super frame.

For DAB broadcasts using MPEG Audio Layer-II or DMB-radio encoding, the indicated broadcast time refers to the start of the transmission frame starting with the MPEG-II transport stream packet that carries the audio signal "A" as the first audio samples encoded into the audio access unit carried in that transport stream packet.

For DAB broadcasts using HE AAC v2 encoding ("DAB+"), the indicated broadcast time refers to the start of the transmission frame starting with the audio access unit that carries the audio signal "A" as the first audio samples encoded into that access unit.

For the digital broadcast systems DAB and DRM, the audio super frame boundaries carrying the audio content "A" should be aligned as closely as possible to meet the timing restrictions described above with respect to the individual audio coding schemes and transmission signal structures.

ETSI

Annex S (informative):

Combined transmission of DRM and FM

A close placement of a robustness mode E signal to an FM signal is possible and can be flexibly configured depending on the existing use of spectrum. In this way, DRM may be introduced into the FM frequency bands.

Figure S.1: Example configuration for DRM robustness mode E and FM signal

Figure S.1 shows that the DRM signal can be placed closely to the left or right of the existing FM signal. To guarantee the respective protection levels and audio quality of the FM signal, the carrier frequency distance ( f) and the power level difference ( P) of the FM and the DRM signals can be planned accordingly. f can be chosen according to a

50 kHz channel raster. f>=150 kHz is recommended. P can be varied flexibly; however, a P>20 dB is recommended for the minimum f=150 kHz.

Two transmission configurations are possible: the analogue and digital signals can be combined and transmitted via the same antenna; or the two signals can be transmitted from different antennas.

Different configurations for the DRM signal are possible. The DRM signal can have the same programme as the FM service, a different programme or the same programme and additional programmes. If the same programme is available via DRM and FM, AFS signalling should be sent in the SDC.

Figure S.2 shows some example configurations.

Figure S.2: Example configuration with 2 FM Stations and DRM robustness mode E

ETSI