Dayton's voice of the arts gets a clearer voice
Apr 1, 2006 12:00 PM, by Jim Stitt
From its rather humble origins in 1985, which included sharing a frequency with the Dayton Public Schools station and using a 200W transmitter and a rooftop antenna, Dayton Public Radio (DPR) has become the pre-eminent source for classical music and fine arts programming in Dayton, OH, and west central Ohio. The 1994 addition of 50kW WDPG in Greenville, OH, to reach the northern areas, and the purchase of FM 88.1 in 1998 for WDPR in Dayton to allow 24-hour operation, gave DPR the capability to reach more than 1.1 million people. By 2004, Dayton Public Radio was poised for its next evolutionary growth step.
This is the production studio with a PR&E console, Enco DAD and Vistamax routing switcher. Only a portion of the extensive CD library is visible.
The WDPR transmitter (original pre-Flexstar configuration).
The Enco DAD automation system, satellite downlink receivers and webcasting.
The ERI panel antenna for WDPR sits at the 880' level on WPTD's tower.
The genesis of this project was an opportunity to relocate and upgrade WDPR's transmitter site from a deteriorating leased tower that was only 200-feet tall, to the local PBS affiliate's 1,500-foot tower. The site relocation was also to include replacing the 30-year-old transmitter that had become increasingly unreliable. Because of the extent of this upgrade, and with the prospect of IBOC on the horizon, former Board Chairman Dr. Michael Jaffe and General Manager Georgie Woessner decided to incorporate a complete facility upgrade to digital at the same time.
The first phase involved the transmitter site relocation to WPTD's 1,500-foot tower with a seven-foot face width. Such a large tower would cause pattern distortion without some form of optimization. Therefore, a single-layer ERI panel antenna was selected to obtain the optimum pattern, fewest nulls and wide bandwidth. The required transmitter power output at the increased antenna height was only 2kW, so low level combining of the analog and IBOC digital signals through a linear solid-state transmitter was the obvious choice.
Processing, on the other hand, is subjective and never involves obvious choices. After polling other classical music stations and conducting listening tests, I chose the Optimod 8400 (being replaced soon with an 8500). A Neustar codec conditioner is also used on the main HD Radio chain and the secondary audio channel (SAC). This configuration has passed muster with the station's golden ears and our critical listening audience.
One of the challenges in adding HD Radio and still preserving the highest quality analog signal involved the STL system. I wanted a system that would deliver uncompressed linear 20kHz stereo audio in AES/EBU, 7.5kHz mono audio for the SCA with radio reading services, a LAN data package with at least 300kHz capacity for the HD Radio stream, data for RBDS and bi-directional data for the remote control. The studios are located downtown, so a line-of-sight microwave path was marginal and vulnerable to new building construction. I investigated the possible installation of fiber to facilitate the bandwidth of an E1 circuit, but the cost was prohibitive. The station was already using Intraplex STLs on T1 circuits, so I next investigated upgrading them. The solution came in the form of a new Intraplex Apt-x card that allowed us to fit everything onto a T1. To avoid problems with the IBOC signal by layering multiple compression algorithms, I did not want to use any digital compression on the main audio channels. However, the Apt-x has proven to be audibly transparent.
The HVAC system is a closed loop with positive pressure in the room to provide the best environment. The transmitter exhaust is vented into the room where two redundant HVAC units control the temperature and the humidity. If both HVAC units should fail, there are high-efficiency pleated intake air filters and a backup exhaust fan. The old transmitter has been installed as a backup analog transmitter with automatic changeover capabilities. The installation also includes a new Burk remote control system with automatic monitoring and logging and an Audemat-Aztec RBDS encoder. Following installation of the antenna, the fine matcher was adjusted to obtain a VSWR of 1.03:1 across the channel. There were some challenges when conducting a proof of performance, as the existing TFT and Belar modulation monitors did not have sufficient selectivity to reject the digital sidebands, so additional external filtering was required. The addition of an HD Radio modulation monitor greatly simplified the process. An Agilent spectrum analyzer verified compliance with the FCC mask.
The next phase involved the conversion of the studios to digital, with the challenge of remaining on the air during the process. I decided to upgrade the production studio first, and then move the on-air operation into production while the air studio was upgraded. A small, temporary editing room was wired to ease the production burden during this transition. The studio walls, soundproofing, HVAC and acoustical treatments did not require any modifications. However, to alleviate existing static problems I did replace the carpet with computer room carbon-backed carpet installed over grounded copper straps using conductive adhesive.
Two PR&E Airwave Digital consoles had previously been purchased to replace the consoles damaged by a water leak, so each studio was designed around them. By using the same model console in both studios, the staff has had fewer problems acclimating. The consoles are reconfigured with appropriate digital and analog cards as required. The consoles output sample rate is fixed at 48kHz, so that is the house standard. The rate conversion to 44.1kHz for the IBOC HD Radio encoder takes place at the transmitter.
Arrakis designed customized studio furniture for the studios to accommodate the non-parallel walls. The audio equipment in each studio includes a complement of Tascam CD players, Sony CDR recorders, Sony mini-disc machines, Panasonic DAT machines, 360 System Digicarts and Alesis Masterlinks. The majority of the classical music library is contained on more than 6,800 CDs, but there are still some rare selections only available on vinyl records. Consequently, a turntable is maintained in each studio. Cassette and reel tape machines are also available for format dubbing when necessary.
My associate, Russ Hines, was primarily responsible for revamping the inter-studio wiring using Gepco and Belden multi-pair analog cables, multi-pair AES/EBU digital cables, multi-conductor control cables and CAT-5 cables. All wiring is color-coded depending on signal type and function, and each wire is labeled at both ends with its number, source, destination and function. A Vistamax 64�64 routing switcher capable of sample rate conversions plus D/A-A/D conversions takes care of signal and control routing for all sources outside each studio as well as multicasting feeds. Any input source, whether digital or analog, is available as a digital and analog output.
A new Enco digital audio workstation (DAW) has been added primarily as a result of the PRSS upcoming Content Depot satellite delivery system. The pier-to-pier network connects the workstations in the air studio, production studio and operation manager's office. All files are backed up on the SATA mirrored hard drives in the air and production workstations. The music is still played live from CDs during the majority of the broadcast day, with the DAW used mainly for satellite assist during overnights as well as pre-recorded programs for holidays. The production DAW uses Cool Edit and is augmented by a 360 Short Cut editor. The Audio Science audio cards provide analog and AES/EBU digital inputs and outputs, and are capable of multiple sample rates, linear uncompressed audio or MP2 and MP3. All sources are converted to uncompressed linear WAV files for the best quality and to avoid artifacts from multiple compression algorithms. Each card offers four outputs, two are sent to the console for that studio, and two are sent directly to the routing switcher for multicast feeds that don't need to go through the studio.
The DPR studios are located in the heart of Dayton's theatre district, so a fiber link was installed between the Schuster Center, Victoria Theatre and the DPR studios to enable live broadcasts of performing arts events. The Multidyne 2200 system is capable of bi-directional video for monitoring the stages, as well as six channels of analog audio and six channels of AES/EBU audio. There is also a statewide T1 system maintained by Etech Ohio (formerly Ohio Educational Broadcasting) linking all public broadcasters in Ohio with bi-directional broadcast quality stereo audio as well as ISDN.
The terminal room contains the satellite downlink and recording equipment for the PRSS system as well as the noisy computer workstations for the Etech Ohio system, the Enco system, the webcast streaming audio and the computers in each studio used to access the www.dpr.org website for updating the current playlist. All workstations use KVM extenders via CAT-5 cable and a master terminal that can access any workstation is available in the terminal room.
The third and final phase, currently underway, is the digital conversion of the WDPG Greenville transmitter site that simulcasts with WDPR. The WDPG transmitter runs a TPO of 12kW, is less than 10 years old and is performing flawlessly. Therefore, I chose a mid-level combining scheme with a solid-state HD Radio transmitter for maximum efficiency and some level of redundancy. An Intraplex T1 STL configuration similar to WDPR's feeds the site. In the final configuration, the HD Radio and all multicasting and data signals are fed into a Harris Importer/Exporter computer. All signal processing is co-located at the studio. The signals are then distributed to each Intraplex STL system, one for WDPR and one for WDPG. The Flexstar exciters at each transmitter generate the analog and digital signals. The digital signal is currently monitored off air with a Kenwood receiver car stereo until the permanent monitors are delivered.
The results of this project have been most gratifying. The signal coverage is at its maximum potential. A-B listening tests with original source material have resulted in unanimous opinions that any differences are indiscernible. Dayton Public Radio's new facility provides the quality, capacity and flexibility to explore and utilize all the potential that HD Radio and Tomorrow Radio multicasting have to offer. Dayton's Voice of The Arts now has the strongest, clearest and most versatile voice in its history.
Andrew HJ7-50A Heliax
Audemat-Aztec FMB80 RDS
Bird BPM power meter
Dielectric RF switch
ERI 1083-1CP panel antenna
Harris Z6HDc transmitter
Harris Dexstar Exciter/Exporter
Harris Flexstar HDX-FM (replacing the Digit exciter)
Intraplex HD STL
Mod Sciences Sidekick SCA
Myat feed line components
Neustar Codec Conditioner
Optimod 8400 (8500)
Andrew HJ8-50 Heliax
Bird BPM power meter
Dielectric IBOC 4.77 combiner
Dielectric RF switch
Harris HT-20 transmitter
Harris Z12HDs transmitter
Harris Flexstar HDX-FM exciter
Intraplex HD STL
Modulation Sciences Sidekick SCA Studios
Electro-Voice RE20 microphones
Enco Systems DAD
Haris PR&E Airwave Digital consoles
Harris Dexstar Exporter
Harris Flexstar HDI-100 Importer
Harris Vistamax 64�64 routing switcher
Multidyne 2200 fiber link
Sage Endec EAS
Sony CDR W66 CD recorders
Sony MDS-E12 mini disc
Tascam 112B cassette
Tascam CD-450 CD players
TFT 990 AES EAS
Stitt is president of JMS and Associates, Cincinnati, OH.