Hidden down a corridor just behind the Orchestra Hall stage is a state-of-the-art recording studio where audio engineer Charlie Post can be found during nearly all of the concerts and many of the rehearsals of the Chicago Symphony Orchestra. He sits at what looks like a kind of command post, with a mixing board and other electronic equipment arrayed around him. During a performance, he follows what is happening onstage via a large video monitor and a walkie-talkie that links him to stagehands (who in turn move and adjust microphones between each work). “It’s a great crew here,” Post said. “Of all the venues I’ve worked at in New York, Miami and wherever else, this is probably the best crew anywhere.”

Almost all CSO concerts in Orchestra Hall are recorded (except for certain performances, such as the CSO at the Movies series). These recordings, which are stored permanently in the CSO’s Rosenthal Archives, form the basis for the 52 weeks of syndicated CSO broadcasts that the WFMT Radio Network presents annually. A select few are transformed into commercial releases with the help of New York-based producer David Frost and distributed via the orchestra’s own label, CSO Resound.

Post joined the CSO staff in September 2014 after 10 years in commercial recording studios in New York City and three years as a free-lance audio engineer for venues in the Miami area, including the Adrienne Arsht Center for the Performing Arts and the Aventura Arts and Cultural Center. In addition, Post worked from 2007 through this year as the chief audio engineer at Ozawa Hall at the Tanglewood Music Festival in Lenox, Mass., the summer home of the Boston Symphony Orchestra. He recently relinquished that seasonal post, because his CSO job was converted to year-round status.

A native of Schenectady, N.Y., Post started playing the saxophone when he was 10 years old. After taking courses in a high-school tech program, he went to college to study electrical engineering but quickly realized the pull of music. Returning home, he enrolled in a two-year degree program at a local junior college devoted to the music business and then briefly worked full time. He later attended the State University of New York at Fredonia, where in 1998 he earned a bachelor of science degree in sound recording technology and a bachelor of arts in applied music performance.

He spends about 60 percent of his work week preparing for and then recording CSO concerts; another 30 percent is devoted to radio production. Post works with a WFMT-FM producer in preparing the orchestra’s recordings for broadcast. He typically picks the best performances from a weekly set of concerts, sometimes splicing a section from one performance with another section from a second or third performance. He also regulates the balances and makes any necessary fixes, such as removing audience noises.

Does the orchestra record everything?

If Maestro [Riccardo] Muti, the music director, is conducting, the concert is recorded. If it’s a guest conductor, we usually record one less concert; so if there are three concerts, two would be recorded. Sometimes, it will be two out of four or four out of five. It just depends on the program.

For the radio broadcasts, how do you decide which performance will be used?

I take copious notes during the performance in the score for each piece, and I put notes right into the computer. After the piece, I’ll usually write, “This performance was the best.” Or, “The second movement from last night was great, but tonight’s third movement was the best.” I will talk to the conductors, whether it’s Muti or a guest conductor, and we’ll have a conversation usually after the last concert and sort of compare notes, but nine times out of 10, we’re on the same page.

What are some of the challenges of the job? What would surprise the average concertgoer?

The fact that a commercial release of classical music is generally edited much more than anyone would ever think. That’s not really a publicly known fact, and when I was working as a full-time music [recording] editor, I had to explain that to people. They’d say, “You’re editing full time?” And I’d say, “Yeah, I’ve got a thousand edits in this 15-minute piece.” It happens. And there are some times where you have two or none at all, and it’s great. But there is typically a lot of editing involved. The amount of time I spend here, I sort of anticipated that, but the radio broadcasts take a lot of time, and it’s one of the hardest things about the job.

What requires so much time?

I’m editing. I’m taking out noises from concerts. For a 20-minute piece, I’m spending at least an hour on that. I had one piece recently where I took out 150 noises for a 25-minute piece. If it interferes with the music, especially in the first minute or two of a piece or a movement, I’ll focus on that. I’ll leave coughs in if it’s going to take the music out.

What is the biggest noise factor?

Coughs and sneezes — the closer they are to the stage, the more they are picked up. The main microphones, the ones that are over the conductor’s head, [they pick up] 90 percent of the sound. So if you are in the third row of the audience, and you cough, it’s going to be just as loud as the clarinet that is equidistant on the other side.

But for radio broadcasts, you typically do fewer edits than you would for a commercial studio recording?

Absolutely. I’m trying to keep the music as pure as possible. The more edits you put in, the more you are sort of manufacturing a performance. The CSO is a fantastic orchestra, so I would rather keep the music that it performs intact.

But if you hear an instrument that is obviously off-pitch, you will fix that in some way?

Yes, that’s a perfect example of why I would make an edit. Or if something is not balanced correctly. Or sometimes it’s an ensemble thing where different people in the orchestra can’t really hear another section very well across the stage.

What are some the biggest changes you’ve experienced in your career?

What was great is that I was working in recording studies during the changeover. I saw the whole thing right in front of my eyes. One day we were recording on two-inch reels at the back of the studio, schlepping these huge [recorders] to the sessions, and within a matter of certainly less than a year, almost everything changed over to recording into a ProTools system on a computer. Of course, the sound changed, but also from a technical standpoint, the computer would crash all the time. It wasn’t just a matter of turning it on and off, but you had to reset it, then figure out how much work you had lost. There were all these frustrations that came along with the early days of computer recording.

Do you think things are better or worse with current recording technology?

It’s just different. The fact that I can record 45 channels — I can actually record up to 64 microphones simultaneously — onto a computer hard drive that is relatively inexpensive is a beautiful thing. The fact that it is not analog tape and maybe doesn’t sound quite as good as recordings that were made in the ’60s through tube microphones [which are now insanely expensive] is the trade-off.

What do you enjoy most about your job?

I love working with the orchestra members. I’m now sending them streaming links of every recorded performance, so they can listen for their own reference and hear what they are doing right and what maybe needs improvement. That’s been big around here. They love it. I’ve had so many positive comments about that. And we offer the same thing for soloists and conductors. It’s saving on our media costs [by not needing to make in-house compact discs, as was done previously], and it’s helping the orchestra. It’s win-win.

While I received a comprehensive education in music [in college], this is a constant source of furthering that education. I’m learning all this repertoire inside and out. I’ve had very few pieces repeat since I’ve been here. So that’s great.

Kyle MacMillan, the former classical music critic of the Denver Post, is a Chicago-based arts journalist.

TOP: Charlie Post in his backstage studio at Symphony Center. | Todd Rosenberg Photography