Live: Yo-Yo Ma and the Colorado Symphony Orchestra

Mar 1, 2010 12:00 PM, By Candace Horgan

CLASSICAL BROADCAST BENEFITS PUBLIC RADIO

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David Day, freelance writer Gary Krakow and consultant Mike Pappas discuss mic placements.

David Day, freelance writer Gary Krakow and consultant Mike Pappas discuss mic placements.

The digital microphones have an NMC DMI-8 8-channel control box that feeds into a Macintosh computer running RCS software. The control box provides phantom power, in this case 10 volts at half an amp, because the mics have a gain stage, A/D chip and DSP chip inside the bodies. From the computer, via the RCS software, Pappas could set many parameters, including compression and limiting, though he used neither. The control box also lets you set the sample rate, which in this case was 24-bit/44.1 kHz.

The reason for the lower sample rate is because the DiGiCo DS-00 broadcast console is limited to 44.1. Pappas has a new SD-7 on order, which will be configured to record up to 24/192 and have built-in Neural Surround. For the CSO broadcast, the DS-00 was used to route the signal.

“We have every imaginable facility on the console, but we don't use it,” Pappas says with a laugh. “For big symphony projects, we don't use any EQ, dynamics processing or the eight stereo reverbs. It's a big level control and router because we route stuff to get it to the broadcast guys.”

In addition to the KM133Ds, Pappas used a stereo dummy head, the KU100 nick-named “Fritz,” in the back of the hall hanging from the ceiling 10 meters above the floor to create the surround rears. “Fritz is an analog box and has standard [analog] outputs,” Pappas says. “We try to not run analog mic cables very long. The cabinet right above Fritz is a Grace 802 unit with a built-in A/D converter that outputs AES. We feed that AES signal down 400 feet of Cat-5 cable.”

In determining how to mike Ma's cello, Pappas had considered employing a KM140 figure-8 in cardioid in a mid-side configuration so that he could control the stereo width. However, his assistants persuaded him to use a Neumann U67 running into a Grace 802 unit in the stage rack above the DiGiCo controller.

When mixing the show, Pappas had a hard-right/left pan of the outside microphones, and the middle three were mixed Lc/C/Rc with the U67 mixed just left of center. Fritz was used for Sr and Sl.

Getting the Right Cables

Not many engineers are concerned with things like audiophile-grade cable, but Pappas has 3,000 feet of Cardas microphone cable for his setup. “We did studies of cable capacitance and the microphones' ability to drive live cables,” Pappas says. “Where this came into play was with applause on live recordings. Typically, you'd have 150 to 200 people and it sounded great; you get to 1,500 or 2,000, and it sounds like crushed pink noise.

“We came to the conclusion that it's not a frequency-response problem or a filtering issue; the microphones run out of current to drive a load so you get this insidious slew-rate limiting distortion,” he explains. “What's happening is the amplifiers in the microphones can't deliver enough current to charge the capacitance at a high level with high-amplitude signals. Once we figured that out, it was an epiphany. We have an Excel spreadsheet that allows you to enter the parameters of a microphone and dial in your cable specs and how much capacitance it has per foot, and it will calculate how much cable length at what frequency you start rolling off and what the slew-rate distortion is, and once we got that done, our applause in the rear channels sounded much better. Low-capacitance cables on analog microphones are the key.”

In addition to high-end cable, Pappas has high-end gear for monitoring the mix: five Avalon Acoustics speakers driven by Jeff Rowland Class-D 1,000-watt amplifiers. The hall's control room was filled with TubeTraps to control echoes.

Controlling the Signal

Pappas paired with David Day of DaySequerra to supply the surround encoding gear. Out of the DS-00 console, the signal was routed into a DaySequerra NLC5.1ST for encoding in DTS Neural Surround. The NLC5.1ST helps control intermodulation distortion without artifacts so that it increases Time Spent Listening (TSL), a key metric for measuring the success of radio programming.

“The DTS Neural loudness algorithm isn't a multiband processor at all; it's a loudness processor,” explains Day. “It speaks to how the ear hears. Its processing is set to be sensitive to the critical bands in your ear. We are the only people on the planet who have anything close to this. Over 250 DTV stations and HD Radio stations in most major U.S. markets are using DTS Neural Loudness Control.”

After going through the NLC5.1ST, the feed went to a DaySequerra DTS DownMix surround encoder and then via ISDN using Telos Zephyr codecs to Colorado Public Radio.

All the digital units were clocked via an external Rosendahl word clock using co-ax. The Rosendahl clocked the Grace M802R preamps, the DaySequerra units, the DS-00 and the Neumann DMI-8.

“What we've found is that jitter is the defining factor in digital audio quality,” says Pappas. “Especially once you start getting into the A-to-D conversion process, if you have a lot of jitter going on at that point, there's nothing that fixes that later — you're stuck. Early on we figured that out and decided we wouldn't buy anything that had anything greater than 500 picoseconds of jitter in the audio passband. Most of the stuff we have now runs in the less-than-50-picosecond range, including the Rosendahl.”

In addition to broadcasting, Pappas and his team recorded the concert in PCM, via Logic 9 on a Macintosh, and in DSD. The DS-00 sent one stream to an EMM Labs up-sampler, then to a Genex 9048 for DSD recording.


Candace Horgan is a Denver-based writer.






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