Orban 5950 Technical Manual Installation 2-5
unmask quantization noise. This is also true of any lossy data reduction applied in the studio (such as hard disk
digital delivery systems).
For MPEG Layer 2 encoding, we recommend 384kB / second or higher.
Some links may use straightforward PCM (pulse-code modulation) without lossy data reduction. If you connect to
these through an AES3 digital interface, these can be very transparent provided they do not truncate the digital
words produced by the devices driving their inputs. Because the 5950’s output is tightly band-limited to 16.5kHz, it
can be passed without significant overshoot by equally well by any link with 44.1kHz or higher sample frequency.
Currently available sample rate converters use phase-linear filters (which have constant group delay at all
frequencies). If they do not remove spectral energy from the original signal, the sample rate conversion, whether
upward or downward, will not add overshoot to the signal. This is not true of systems that are not strictly band-
limited to 15 kHz, where downward sample rate conversion will remove spectral energy and will therefore
introduce overshoot.
If the link does not have an AES3 input, you must drive its analog input from the 5950’s analog output. This is less
desirable because the link’s analog input circuitry may not meet all requirements for passing processed audio
without overshoot.
If you use a digital link to pass the digital composite output, the link must be uncompressed. We recommend not
using sample rate conversion in such a link, as sample rate converters may introduce filters that compromise
stereo separation.
Composite Baseband Microwave STLs (Analog and Digital): The composite baseband microwave STL carries the
standard pilot-tone stereo baseband and therefore receives the output of a stereo encoder located at the studio
site. The receiver output of the composite STL is the stereo baseband signal, which is applied directly to the
wideband input of the FM broadcast transmitter’s exciter. Thus, no stereo encoder is needed at the transmitter.
In general, a composite microwave STL provides good audio quality, as long as there is a line-of-sight transmission
path from studio to transmitter of less than 10 miles (16 km). If not, RF signal-to-noise ratio, multipath distortion,
and diffraction effects can cause serious quality problems. Where a composite STL is used, use the 5950’s stereo
encoder to drive the composite STL transmitter.
Uncompressed digital composite baseband microwave STLs, if properly designed, have excellent performance and
we recommend them highly. They are particularly desirable in an 5950 installation because they allow you to use
the 5950’s composite limiter to increase on-air loudness.
However, the fact that they are digital does not eliminate the requirement that they have low frequency response
that is less than 3 dB down at 0.15 Hz. Any such STL should be qualified to ensure that it meets this specification.
Dual Microwave STLs: Dual microwave STLs use two separate transmitters and receivers to pass the left and right
channels in discrete form. Dual microwave STLs offer greater noise immunity than composite microwave STLs.
However, problems include gain- and phase matching of the left and right channels, overloads induced by pre-
emphasis, and requirements that the audio applied to the microwave transmitters be processed to prevent over-
modulation of the microwave system.
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