Test and Measurement Needs for the Shop
I wrote earlier that you used to be able to use your ears to troubleshoot many problems around the radio station. In today's environment you need an electronic interface of some sort (instead of headphones). For tracking down digital problems a very common pair of items is the Ward-Beck ABS-1 (Audio Bit Spitter) and the ABB-1 (Audio Bit Buddy). With the ABB-1, digital and analog program audio can be monitored by the headphone output while the L/R levels are displayed on LED bargraph meters. Critical signal parameters such as sampling frequency, emphasis, professional/consumer format and data errors are displayed when monitoring AES/EBU or S/PDIF signals. Digital input monitors sampling frequencies from 30kHz to 50kHz automatically.
The ABS-1 is the AES generator. It's battery powered, and it generates an AES3 digital data stream (with sample rates of 32, 44.1 or 48kHz) with audio levels (encoded in the data stream) of -20, -12, and 0dBFS. It also generates analog outputs at levels of -16, -8 and +4dBu (on 1/4" TRS connectors). To distinguish between the CH A and CH B (left and right) signals, the unit provides the option to cycle and/or invert the CH B (right) signal or to turn it off completely.
Another option for a hand-held digital audio analyzer is the NTI DL1. The DL1 measures multiple aspects of the AES data stream, such as carrier level and sample rate, and channel status for professional or consumer mode. It continually checks the integrity of the incoming data stream and will alert the user to inconsistencies, and since it has built-in logging it can more easily help the user figure out intermittent issues. Decoded audio is available on a small speaker and headphone output. Included also is a small time-domain display (kind of like a mini-oscilloscope) that displays the decoded audio. Beside peak level measurements, the DL1 is equipped with RMS measurement techniques including THD+N and high pass filters, allowing verification and debugging of dual domain devices such as A/D converters.
The complementary signal generator for the DL1 is the DR2. This device has a transformer-balanced output for AES3, and also S/PDIF, TOS-link and ADAT outputs. The internal low jitter clock generator can be synchronized to AES3, DARS, word clock and video signals. Measurement of channel transparency, channel propagation delay and sample frequency is supported. The DR2 has the digital audio test signals used for maintenance and repair of digital audio systems, but the user can store his own test signals as WAV files in the DR2's memory.
- continued on page 4
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