Broadcasting the Colorado Symphony Orchestra

March 1, 2010

On Location, March 2010

When the Colorado Symphony Orchestra began to feel the economic pinch this year, it came up with several novel ways of addressing potential budget shortfalls. In addition to across-the-board pay cuts, the CSO teamed with Colorado Public Radio for a three-day pledge drive that culminated with a concert with acclaimed cellist Yo-Yo Ma.

Yo-yo Ma

CPR broadcast the CSO/Yo-Yo Ma concert live to 22 radio stations in Colorado in DTS Neural 5.1 Surround. All told, the drive raised more than $600,000.

When the CSO looked into having the concert broadcast, it selected someone it worked with before, Mike Pappas. Pappas has been recording "forever" in his own words. "I sold my car and bought a Scully 280 two-track, ¼" tape recorder, which I used to carry in a flight case and lug around to gigs," he says. "It weighed like 90 pounds. I had 14" reels on it so I could actually record for an hour."

Setup problems

Pappas is technically an independent consultant, though he often works with KUVO Public Radio and considers it home base. He first worked with the CSO in 2004, on a recording of Dianne Reeves playing the CSO.

Mike Pappas checks mic placements while David Day looks on.

Mike Pappas checks mic placements while David Day looks on.

"The CSO called us a couple years back to do 10 days of Beethoven, so we loaded in May 28 and were out of here on June 13," explains Pappas. "There were usually two performances a day, or a rehearsal and a performance. None of those rehearsals and performances were the same, so you'd rehearse one thing and they'd be performing something different that night. I think we had, at one time, 12 different sets of tape marks on the hall floor as to where microphone moves were for specific events. We had to take the stage apart from the morning rehearsal and then put it back up for the evening performance."

Radio magazine's sister publication Mix magazine was also on-site during the event. Read Mix's account of the event.

The Boettcher Auditorium itself is idiosyncratic, with several problems an engineer has to consider in setting up a recording.

"The whole hall is in a really weird spot," laughs Pappas. "Half the audience is behind you and none of the seating areas are symmetrical. It's hard to find a center line in that room. It has quirks, like players on the right hand of the stage can't hear players on the left hand of the stage. It's particularly interesting problems out there, so all that plays into gear we use and how we get it to work."

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On Location, March 2010

Microphone paradise

On a tour of KUVO, Pappas' assistant Will Barnette unlocked the equipment cabinet and revealed a Neumann lover's paradise, with M150s, U87s, a U67 and more. For the Yo-Yo Ma concert, which was held in the Boettcher Auditorium, Pappas turned to a prototype Neumann microphone, the KM133D, a digital microphone. The microphone uses an M50 titanium capsule, which Pappas said is ideal for many classical applications.

Pappas sets levels before the concert.

Pappas sets levels before the concert.

"It's mounted in a sphere, so at low frequencies the microphone is an omni. As we get above 1kHz the microphone develops a cardioid pattern. Then above 16kHz it's a hyper-cardioid," explains Papas. "With classical work, that allows you to be real creative. Being omni at low frequencies allows us to integrate some of the room tone. The other cool thing about omnis is they are extremely flat in their frequency response. Now, the Germans won't tell you this, but the capsules on those digital mics, or the M150s for that matter, are 3dB down at 2.5Hz. We have lots of low frequencies, and that's good, because you don't want to have rolloff that's going to look back anywhere into the audio passband. You want to keep that as far out of the audio band as possible, because the minute you have a rolloff, you have a phase shift. Omnis are cool for that, but the problem with omnis is they are omnis, so you want something with some directivity at high frequencies, because it allows you to aim the microphones into the orchestra and use that directivity to help bring out certain sections of the orchestra.

Pappas used a total of five in front of the stage, using tape to mark the placement of each microphone to within a quarter of an inch, since they had to take them down after each morning rehearsal. The microphones were placed 10'3" above the stage, aimed slightly down at a five degree angle. Barnette and Joey Kloss helped Pappas place the microphones and take them down each day after rehearsal.

The digital microphones have an NMC DMI-8 eight-channel control box that feeds into a Mac running RCS software. The control box provides phantom power, in this case 10V at 0.5A, because the mics have a gain stage, A/D chip and DSP chip inside the bodies.

A mic named Fritz

From the computer, via the RCS software, many parameters can be set, including compression and limiting, though Pappas used neither. The control box also sets the sample rate, which in this case was 24-bit/44.1kHz. The reason for the sample rate is the console, in this case a Digico DS-00 broadcast console, which runs at 44.1kHz.

Making final settings on the surround encoder

Making final settings on the surround encoder

"We have every imaginable facility on the console, but we don't use it," laughs Pappas. "Let me qualify that; 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, which he and his team have affectionately nick-named Fritz, back in the hall hanging from the ceiling 10 meters above the floor to create the surround rears. Fritz was aimed at the back of the hall, instead of at the orchestra, to get more of the room integrated into the surrounds.

"Fritz is an analog box and has standard (analog) outputs," says Pappas. "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' of CAT-5 cable. We use CAT-5 because it is very low capacitance, and capacitance is the number one killer for AES. You don't necessarily need it shielded because it's a balanced signal coming off 7.5-8V peak to peak."

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On Location, March 2010

Miking Yo-Yo Ma

One big point of contention for Pappas and his team had to do with how to mic Yo-Yo Ma's cello. Pappas was leaning toward a KM140 figure-8 and cardioid in a mid-side configuration during the rehearsals, so that he could control the stereo width. Ultimately, Pappas's assistants persuaded him to use a Neumann U67 and all its tube glory, running into a Grace 802 unit in the stage rack above the Digico controller.

The Avalon Acoustics speakers placed in the surround monitoring positions.

The Avalon Acoustics speakers placed in the surround monitoring positions.

Not many engineers are concerned with things like audiophile-grade cable, but Pappas has 3,000' of Cardas microphone cable for his setup.

"We studied cable capacitance and a microphone's ability to drive live cables," says Pappas. "Where this came into play was with applause on live recordings. Typically you'd have 150-200 people and it sounded great; you get to 1,500-2,000 and it sounds like crushed pink noise. I heard a lot of this on classical recordings too, and we started looking into what was causing it.

"We came to the conclusion that it's not a frequency response problem or a filtering issue, it's the microphones running out of current to drive the load, so you get this insidious slew rate limiting distortion. 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 spread sheet that allows us to enter the parameters of a microphone, dial in the cable specs and how much capacitance it has per foot, and it calculates the cable length and frequency at which things start rolling off as well as the slew rate distortion. 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 equipment for monitoring the mix. He uses five Avalon Acoustics speakers driven by Jeff Rowland Class D 1,000W amplifiers. The control room in the Boettcher was filled with tube traps to control echoes.


When mixing the show, Pappas had a hard right/left pan of the outside microphones, and the middle three were mixed left center/center/right center, with the U67 mixed just left of center. Fritz was used for SR and SL.

Pappas also paired with David Day of Day Sequerra for the surround encoding equipment. From the DS-00, the signal was routed into a Day Sequerra NLC5.1ST for encoding in Neural Surround. The NLC5.1ST helps control intermodulation distortion without artifacts, so that it increases time spent listening (TSL).

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On Location, March 2010

"The Neural Loudness Processor isn't a multi-band processor at all; it's a loudness processor," explains Day. "It speaks to how the ear hears. It's processing is set to be sensitive to critical bands, ERB's, in your ear. About 600 radio stations and about 2,000 TV stations in the U.S. are using it right now.

After going through the NLC5.1ST, the feed went to a Day Sequerra DTS Downmix Surround Encoder, and then via Telos Zephyr Xstream (ISDN) to Colorado Public Radio.

All the digital units were clocked via an external Rosendahl word clock using BNC coax connectors. The Rosendahl clocked the Grace 802 units, the Day Sequerra units and the NMC 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/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 100 range."

In addition to broadcasting, Pappas and his team recorded the concert in both PCM, via Logic on a Mac, and in Direct Stream Digital (DSD). The DS-00 sent one stream to an EMM Labs Digital-to-Analog converter, then to a Genex 9048 for DSD recording.

Horgan is a freelance writer based in Denver.

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