Studio Transmitter Link
When the broadcast studio and transmitter sites are in different locations, you will need a Studio Transmitter Link or STL. It is required to send radio content from the broadcast studio to the transmitter.
The STL can be wireless (terrestrial or satellite), a digital point-to-point connection, or a VPN network. Today even the public Internet is used by many operators as STL.
On localdab.org, we use the mnemonic STL in the first architecture to link the broadcast studio to the multiplex (MUX) provider by an intermediate standard audio encoder as we use for Internet radio.
Or, in the case that de DAB+ encoder resides in the broadcast studio, we use STL for the connection between the DAB+ encoder and the multiplexer (without any intermediate encoder/decoder).
We need to make a distinction between these two architectures.
The first one is low-budget and less professional. Most of the time, it is the origin of low-quality audio. The second digital conversion (can be both audio format as well as sample rate conversion) plays an important role in the audio quality. However, in Belgium and the Netherlands, almost all small-scale DAB+ radios use this architecture, although many also complain about bad DAB+audio quality.
For optimum audio quality radio broadcasters will use the second architecture, which also makes adding frequently changing additional information from the playout system easier.