3-12 Operation
Certain unusual program material may cause infrequent instances of gain reduction as high as 12 dB with the
above settings. This occurs on isolated transients and is no cause for concern unless it is frequent.
Except for the fact that its input has been de-emphasized, the HD look-ahead limiter receives the same processing
as the FM peak limiting section if the FM->HD CONTROL COUPLING is set to FM->HD. Earlier processing has often
been adjusted to help compensate for the inevitable high frequency loss caused by pre-emphasis limiting in the FM
peak limiter. Therefore, the HD output can be excessively bright without further adjustment.
In FM->HD mode, you can use the 5950’s parametric high frequency shelving filter to supply a high frequency
rolloff that tames excessive brightness in the HD output. Simultaneously, this HF rolloff may reduce high frequency
artifacts in the relatively low bite-rate codec used in the Xperi HD Radio system.
With the FM->HD CONTROL COUPLING set to INDEPENDENT, there are several approaches to minimizing
brightness and conditioning the signal to work well at low bitrates.
x Use little or no high frequency boost in the HD equalization and band mix sections.
x Set the HD BAND 4>5 COUPLING to 100%.
x Set the HD B5 THRESH to match the codec and its bitrate. Adjust the threshold until you find a good
compromise between presence and high frequency codec artifacts. We find the range from -6.0 to +6.0 dB to
be useful.
x Use a moderate Band 5 attack time. 25 ms works well.
x If necessary, lower the HD B4 THRESH.
BS.1770 Compliance for Digital Radio
The 5950 includes an ITU-R BS.1770 Loudness Meter and Safety Limiter in the digital radio processing path. The
Safety Limiter should only be activated if the regulatory authority in your country requires constraining BS.1770
Integrated Loudness to a specified threshold.
Input/Output Delay
The sophisticated look-ahead algorithms in the 5950 have one significant cost—the input/output time delay is
longer than that of an analog processor and can cause problems if an off-air pickup is used to feed talent
headphones.
To make intelligent decisions about how to process, the 5950 needs to look ahead at the next part of the program
waveform.
(Slowly changing bass waveforms require particularly long look-ahead delays.) As digital on-air processing
advances further and further from its analog roots, this is the inevitable price of progress.
The amount of delay depends on several things. Because of their unprecedentedly sophisticated processing, “MX”
presets introduce delays of approximately 265 ms, which makes real-time monitoring through headphones
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