Field Report: APT/Pulsecom PCAU

Since its inception in 1936, WQXR-FM has built a strong reputation as New York City's premier classical music radio station, and is proud of the fact that it was the first commercial classical station in the United States. Now owned and operated by The New York Times Company, which acquired it in 1944, WQXR is the most listened-to classical station in the United States and presents regular news, analysis and commentary, often featuring correspondents from the New York Times. WQXR's signal emanates from the top of the Empire State building and covers the five boroughs of New York City, northern New Jersey, Long Island, Westchester, Rockland and Putnam Counties and Fairfield, CT.

WQXR-FM has always been at the cutting edge of technological innovation. Major Edwin Armstrong conducted the first FM stereo tests on WQXR, and our AM outlet was the first AM stereo station in New York.

During 2002, WQXR decided to move the station's newsroom from its main Union Square District studios on 5th Avenue to the Times' newsroom located in the New York Times building on 43rd street in the heart of Times Square. The advantage being WQXR's news people could use the resources at the Times, as well as collaborate with their colleagues at the newspaper and NY Times Digital, which creates the New York Times on the Web.

Moving an entire newsroom and announce booth a distance of 30 blocks was an issue in itself, but the bigger challenge was routing the news feeds on an hourly basis from the New York Times to WQXR. In addition to construction and acoustical issues, this meant establishing a new bi-directional link between our studios and the New York Times offices.

Historically, the local telephone company could, with sufficient notice, install balanced copper circuits for remote or studio-to-transmitter links. However, in recent years this technology has become harder to support and the onerous task of balancing the circuits has resulted in the telephone company's decision to no longer support this service.

Faced with this situation, I began looking at alternative technologies that might fill the vacuum. The best of these invariably required proprietary HDSL availability, thus adding a considerable delay to installation time. There were also loop-length issues involved, and problems with preserving dynamic range throughout the broadcast chain — something that is particularly important when you're dealing with classical music and traditional jazz.

Performance at a glance
20Hz to 15kHz frequency response
Low latency; less than 4ms
Front-panel status LEDs
Uses the Apt-x algorithm
Standard 2B1Q U interface

After much deliberation, our local telephone company, Verizon, recommended a service using a Program Channel Access Unit (PCAU). This encoder/decoder card, which was developed as a joint venture by Belfast-based Audio Processing Technology (APT) and U.S.-based Pulse Communications (Pulsecom), uses APT's Apt-x 4:1 data compression algorithm as its core technology. It will pass an 8kHz or 15kHz mono signal over 64kb/s or 128kb/s links respectively, enabling broadcast-quality audio from any D4, DLC or NGDLC carrier system. In the PCAU format, the Apt-x algorithm is implemented on boards incorporating Pulsecom's ISDN U interface and featuring plug-and-play Type 400 mechanics and network standard loopbacks.

I worked with the Apt-x algorithm before in an STL product and an automation product, and was satisfied with the performance of the compression algorithm, particularly with the low delay (latency) and the good audio response. This was reaffirmed after an in-house demonstration from Verizon.

However, once convinced of the technology, I had to order the service — in this case a 15kHz mono, full-duplex link that I required for the news feeds. The bandwidth was necessary to implement the maximum performance of the PCAUs and the return feed was needed for talkback and monitoring.

With four weeks to go before we were scheduled to move the newsroom, my main concern now was how long it would take to install the service. I also was concerned about the number of central offices that would be used to route the signal. Would both issues result in unworkable or unmanageable delays?

The Verizon staff surpassed their best efforts and managed to install the service in less than two weeks, routing the signal via three central offices at 18th St., Broad St. and 42nd St. The speed of the install was aided by the fact that the PCAU cards use telco-standard 2BIQ 128kb/s technology for data interface. Once installed, the low-coding delay of the Apt-x algorithm — less than 4ms end-to-end at a 32kHz sampling rate — allowed our newscasters to monitor their own voices off air after the program content had gone from WQXR to the New York Times newsroom, back to WQXR and then via STL to broadcast from the Empire State Building. The total delay was a manageable 20ms, and it sounded excellent.


I ran some tests on the link and the dynamic range was close to the maximum of 96dB for 16-bit audio. Headroom was 24dB and the response was flat from 20Hz to 15kHz. With the front panel indicating power, network, far-end synchronization and audio level, I had status at a glance, which is always a comforting feature for a station engineer.

For WQXR, the PCAU card addressed a number of problems without compromising audio quality or delay. The newsroom is running successfully from its new location and to date we are satisfied with our chosen solution. The problem was solved so effectively that now I am considering the PCAU card for additional voice and music circuits in the near future.

Belizaire is chief engineer of WQXR-FM, New York.

Editor's note: Field Reports are an exclusive Radio magazine feature for radio broadcasters. Each report is prepared by well-qualified staff at a radio station, production facility or consulting company.

These reports are performed by the industry, for the industry. Manufacturer support is limited to providing loan equipment and to aiding the author if requested.

It is the responsibility of Radio magazine to publish the results of any device tested, positive or negative. No report should be considered an endorsement or disapproval by Radio magazine.

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