We also thought of Dan Slentz, who has built at least three LPFMs that we know of (not to mention his impressive broadcast credentials as a radio and TV engineer and director of Blue Stream Media at John Carroll University). Dan knows broadcast, yes, but he also knows streaming as the advisor to WDOG 105.9 LPFM in New Philadelphia, Ohio, which made him the perfect candidate to try out our new Linux streaming appliance.

He agreed to take a look and listen, largely because he said he was intrigued by all the features. Wheatstream Duo has everything needed for provisioning streams and managing metadata for two channels, four outputs each, right down to LUFS metering. Dan especially liked that Wheatstream Duo is a Linux appliance that costs about the same as a decent streaming PC. He recognized that being able to switch over to a Linux appliance gave WDOG LPFM a lot more stability and reliability. “They’ve built this on a very rock-solid Linux system so no need to ever worry about Microsoft or Apple running patches, updates, or fixes or viruses or ransomware,” he commented.

And, of course, he was especially curious about Wheatstream Duo’s audio processing designed specifically for streaming. Dan became a fan of Wheatstone on-air audio processors years ago when he installed one of our FM processors for a new format launch in Dallas. “Within minutes [of putting it] on the air, I got a call from a retired engineer… who said ‘I don’t think I’ve ever heard a station sound so good!,’” he commented.

When it came to new products, he added, “If it had the Wheatstone name, I had confidence that the company would make a very high-quality product and stand behind it.”

 We sent him serial number 0004, one of the first Wheatstream Duo units to come off the line. He told us right off that setup was relatively easy and that he was impressed by all the work we put into the audio processing. And it’s true. We didn’t just settle for all the audio processing techniques we knew and developed over the years for on-air. Our Jeff Keith had spent a lot of time in the lab coming up with ways to make streaming music pop while controlling incoming levels and outgoing peaks—all without upsetting the streaming codec.

Streaming Processor Inside

We know Dan to be an outspoken critic of source material, namely that music from the old days sounds lifeless, while more modern music mastered today is often, as he stated in a Radio World article, “either recorded too hot and clipped or processed out the wazoo to begin with.”

As a rock station, WDOG LPFM operators deal with those challenges daily. The same source music that feeds the FM signal also feeds the streaming channels, which requires an entirely different kind of AGC because of the streaming codec. We learned early on that perceptual codecs, while great for removing insignificant audio details to fit programming within the constraints of a typical Internet link, don’t do well with aggressive processing. Codecs are especially sensitive to intermodulation distortion, which they often mistake for audio and therefore tend to “spend” bits on instead of actual audio. This can be especially noticeable on low-bitrate streams.

To manage levels in streamed content without triggering the codec, we use predictive dynamics control and neural network techniques in our streaming appliances to create extremely natural management of program dynamics and spectral balance.

Then, to manage transient peaks and keep overshoots well within the codec’s 0 dBFS threshold, where it essentially runs out of bits, Wheatstream Duo uses proprietary multiband peak limiters managed by Peak Energy Estimators to control peak energy without creating dynamics-related artifacts. Final limiting also occurs separately in two frequency bands to provide a balance between high perceived audio quality and stream loudness. For streams of very low bitrates especially, removing low frequencies in the stereo difference channel (L–R) can leave more bits available for encoding upper frequencies in the L–R that are more perceptibly useful. 

Dan started with one of the 50+ presets in the Wheatstream Duo and slowly made modifications over a couple of days. Within a week, #0004 wasn’t going anywhere and had found a permanent home at WDOG LPFM.