As Vorsis Senior Product Development Engineer, Jeff Keith has not only designed audio processors for over 30 years, but also spent a lot of time in the field helping customers set them up properly. He shares some of his thoughts on the art and science of tuning up audio processing to get the sound you want.
His first bit of advice might surprise you: Listen to the competition in your market. If you have a frequency-agile modulation monitor, that’s great. Otherwise, pick a receiver that you know and trust. What you hear will determine what to do next.
“Lots of engineers want to be the loudest station in the market. But how loud is your competition, and how do they get that way?” asks Keith. “Some stations don’t play by the rules, and you’ll see 130 percent modulation along with deep composite clipping.” He adds that you too can break the rules, or choose a different path.
Keith explains that those who push their stations’ modulation beyond the legal maximum may not understand that the linearity of many receivers is doubtful beyond 100 percent modulation. This may cause distortion and listener fatigue to increase dramatically. “Gross overmodulation can create nasty distortion in listeners’ receivers that is beyond your control. Maybe you can’t stay legal and be the loudest, but you can definitely be the cleanest, and you’ll hold on to your listeners for longer periods.”
To set up audio processing for a great sound, you need the right tools. A calibrated modulation monitor with a multipath-free signal is a must. Peak flashers differ, even on calibrated monitors, depending on whether it has the 900 microsecond “forgiveness factor” peak standoff option. Some are adjustable, but it is important to understand how yours works. A call to the manufacturer may be in order.
An oscilloscope set in the X-Y mode is also essential. “There is no other way to visualize as many parameters of your signal simultaneously as with a scope,” adds Keith. The scope need not be expensive; a dual-trace 10 MHz unit will do fine, as long as both X and Y channels have equal gain and bandwidth.
“With a good stereo signal, you’ll want to see a big, round fuzzball,” explains Keith. “If it turns into a hard-sided diamond, there’s heavy clipping going on somewhere.” He adds that a mono signal, such as voice, should be a straight diagonal line. If it hooks on the ends or is more vertical or horizontal, there is a channel imbalance in the audio chain.
Finally, Keith notes that engineers need to have realistic expectations from a processor. “It cannot perform acts of magic or defy the laws of physics,” notes Keith. A clean audio plant is essential to great sound. “With audio processing,” he adds, “it’s a case of garbage in, worse garbage out.”
“Many stations haven’t performed a proof-of-performance in years,” notes Keith. “Some are under the misconception that modern audio gear is maintenance free, and proofs went out of vogue with vacuum tube gear. Emphatically not true.”
He adds that in analog signal paths, electrolytic coupling capacitors can dry out, resulting in degraded frequency response and distortion. Amplifier gains can shift, causing channel imbalances and degraded separation. Connectors can oxidize, especially seldom-used XLRs and patchbays, resulting in intermittents and gritty sound.
Digital plants need to be watched for cascading compression algorithms and multiple A to D and D to A conversions. It’s also important to check that all material in the playout system is standardized on linear digital audio, rather than compressed file storage such as MP3s.
Final tweaks may be made via a laptop connection back to the processor, and in a more controlled listening environment such as a production room, but even here there can be pitfalls. It is important to know your monitoring gear and what sounds normal, both for your station and the competition. “The worst thing that you can do is buy a new amp, speakers and headphones and start playing with the processing, because you have no point of reference,” explains Keith. Two other “bads” are adjusting the station’s processing to fix one nasty sounding record when everything else sounds great, and trying to adjust audio processing by committee. We all hear things differently – pick one “golden ear”person who knows what the goal is and give that person the final say on the station’s sound. Then comes the hardest part for most processing “tweakers”: stop adjusting when they tell you you’ve nailed it!
Finally, Keith concludes that sometimes station personnel can obsess too much on nuances that only “radio people” hear or even know to listen for. “Listeners tune in to a station because it has the content they are interested in. They usually don’t know or even care who is the loudest, who is winning the bass race, or who has the most sizzle in their high end.”