Why is PCAU audio so much better?

This is a long answer, but there are lots of reasons.

Conventional Program Channel Units use "J.41" audio processing. Although adequate when first developed 20 years ago, J.41 can't reproduce the low frequency and mid band "punch" typical of modern CDs, and exhibits noticeably more background hiss.

The alternative to antiquated J.41 audio is the revolutionary Audio Processing Technology's apt-XT algorithm found in the Pulsecom/APT Program Channel Access Unit, or PCAU. Heard world-wide in digital movies and used by flagship radio stations like the New York Times' WQRX, the apt-XT has set a new standard for audio quality for a number of very specific reasons.

  • J.41 is based on 14-bit Pulse Code Modulation (PCM) and 14-bit-to-10-bit compression and expanding (companding) techniques. The apt-XT uses a 16-bit algorithm and Adaptive Pulse Code Modulation with Predictive Analysis and Backward Adaptation to achieve loss-less, low delay, low latency audio processing. As a result, the apt-XT offers a 96 dB dynamic range as opposed to the 84 dB range provided by J.41. The 12 dB boost in dynamic range delivers:
    • Improved headroom, reducing the possibility of distortion during loud passages.
    • Improved Signal-to-Noise performance, reducing the possibility of Ground Floor Noise (i.e. "hiss") break-through during quite periods.
    • Protection from even worse noise, hiss and corruption that is a characteristic of multiple J.41 A-to-D and D-to-A conversions in remote-to-studio-to-antenna broadcast links and similar configurations.
  • J.41 bandwidth is only specified as 40Hz to 15kHz. The PCAU is virtually flat down to 10Hz, providing impressive bass response.
  • Unlike J.41, which simply assigns equal weighting to its entire 40Hz to 15kHz bandwidth, the apt-XT algorithm allocates seven of its 16 encoding bits to the critical 10Hz to 3750Hz frequency band - the area that contains most music and voice program information. The result is noticeably better "punch" and "immediacy" while remaining very true to content at the top end thanks to 16-bit encoding.
  • Independent and "Double Blind" Listening Tests have proven the apt-XT algorithm outperforms J.41 with highly transient Classical or Digital Effect music.
  • The PCAU uses 24-bit processing to eliminate encoding and decoding rounding errors and further optimize audio performance.
  • Digital audio transmission is susceptible to bit errors which can cause audible pops, glitches, and drop outs. The PCAU makes use of APT's exclusive AutoSyncT technology to provide real-time protection from this common problem.

Does the PCAU support 5kHz, 7.5kHz, 8kHz and 15kHz services?

Yes. Earlier generation telco Program Audio products required different units for each bandwidth. A single PCAU handles all of the above bandwidths.

Are there "Transmit PCAUs" and "Receive PCAUs"?

Earlier generation telco Program Audio products required one type of unit for transmit and a different unit for receive. Each PCAU can be set to "Transmit" operation or "Receive" operation via a front panel switch.

My audio circuit has a 10dB loss. Can the PCAU deliver 0-loss circuits?

Yes. The PCAU supports both 0-loss and 10 dB loss circuits.

Can I buy a PCAU and connect it to a phone company network?

Yes, in two applications:

  • "Campus" connections over a continuous unshielded (or shielded) twisted pair phone wire that is less than 3 miles long.
  • If you lease a T1 line and have channel bank equipment at each end and if the channel bank can be equipped with "U-Interface line cards," the PCAU can be connected to these U-Interface cards.

In most applications, PCAU users have found it to be less expensive to contact their telephone company and order digital program audio services, making sure that the phone company will use the PCAU (most major carriers do). This approach not only saves money, it also eliminates the need to buy a PCAU (the PCAU is owned by the phone company and part of your monthly service fee), and includes 24x7 phone company circuit support.

Does the PCAU support mono and stereo?

Yes. In stereo applications, a pair of PCAUs at each end are linked with a stereo synchronization cable to assure that left and right channels are phase-aligned within a few degrees in accordance with ANSI standards.

Can the PCAU support HD Radio?

An HD-PCAU will be available in mid-2006. Some features:

  • Backward-compatibility with far-end PCAUs to simplify network transitions
  • 20Hz to 20kHz apt-XT audio
  • Analog or digital 20kHz audio transport
  • RDS support

The HD-PCAU plugs into existing PCAU shelves to further simplify transitions.

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