DO THIS BEFORE RACKING UP A NEW PROCESSOR

Our processing genius Jeff Keith has some sage advice regarding levels and STL paths when racking up that new processor. You never know when there might be a new audio processor on the market worth checking out (wink, wink).

Make sure input levels are set for adequate headroom. The recommended practice for setting input levels on digital studio gear is -20 dBFS average, -12 dBFS peak. This provides, on average, 20 dB headroom before the absolute maximum level of 0 dBFS is reached. Why is this so important? One of the first things an on-air processor does to the incoming audio is pass it through a phase rotator to make asymmetrical waveforms, like speech, more symmetrical. By its very nature a phase rotator increases the peak level of clipped waveforms and often by as much as 12 dB (or more) depending on its filter order. Worse, most processors meter the input levels before filtering and phase rotation so a user never knows (and can’t see!) that they might be out of headroom even with happy input level meters. In short, setting studio gear to a standard input level with enough headroom will give the processor more to work with and result in a better sound overall. 

Choose a linear STL path, if possible. It’s not always possible to have a linear STL path, but if you’re given a choice, do so. You also will get better results with a composite rather than a discrete AES left and right STL. This is because the stereo generator in a modern audio processor is almost always better than one built into an exciter. Also, once you get your new processor, plan on sending the complete composite baseband over AES, from the processor to the exciter in full digital form. This gets rid of the AD/DA between the two as well as the noise resulting from an unbalanced analog signal in the transmitter building. Wheatstone processors include the baseband192 feature for this purpose. 

As you begin to experiment with your new audio processor, Jeff suggests you use a good reference radio you’re familiar with, and that you start with a conservative preset.

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