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Review: Audio Precision APx525 Audio Analyser

SILICON CHIP has a long record of using the latest available instruments to validate our designs - typical of this has been our use of the Audio Precision System One to measure all our high performance audio designs. This month we review the latest such instrument from Audio Precision, the APx525.

By Allan Linton-Smith & Nicholas Vinen

Basic Specifications:

Output frequency range: 0.1Hz-80.1kHz

Output frequency accuracy: 2 ppm

Maximum output amplitude: 30V peak

Maximum input voltage: 300V RMS (balanced)
/160V RMS (unbalanced)

Input bandwidth: >90kHz

Input/output amplitude accuracy: ±0.05dB

Input/output amplitude flatness: ±0.008dB

Residual input noise: 1.3µV

Input/output residual THD+N: -105dB + 1.4uV

Digital sampling rate: 22kHz-192kHz

Digital output formats: PCM, Dolby Digital, DTS

As with previous Audio Precision analysers, the APx525 is essentially a computer peripheral. It relies quite heavily on digital signal processing and much of this is done using the host PC, connected via USB 2.

This is much more convenient than the dedicated interface cards needed for some of the older analysers and a mid-range laptop is more than enough to drive it. Everything is controlled by the computer and the analysis results are displayed on its screen.

The APx525 adds many new features and capabilities compared to its predecessors. Its design was influenced by an internet survey of engineers and Audio Precision users. The results of this survey showed a need for a digital audio analyser with HDMI and Bluetooth interfaces along with a variety of other wish list items. The result is an unprepossessing instrument 432 x 467 x 129mm, weighing 10.9kg.

There are no controls on the unit itself – the front panel consists mainly of input and output connectors to interface the unit with the device under test (DUT).

In addition to the XLR, BNC and banana connectors for the balanced and unbalanced stereo audio inputs and outputs, it has TOSLINK, BNC and XLR (AES/EBU) sockets for digital audio input and output.

Using the software, you can easily set it up to use any combination of these, to suit the instrument you are testing.

The digital audio interface supports sampling rates of 22kHz-192kHz and resolutions of 8-24 bits. As well as linear PCM, the digital output can generate Dolby Digital and DTS signals, to interface with home theatre gear.

HDMI, Bluetooth and other interfaces are added with optional modules – there is space for both.

The combination of analog and digital inputs and outputs allows a variety of equipment to be tested. You can test analog devices such as preamps, amplifiers and filters but then you can also test DACs (digital-to-analog converters) or digital home theatre receivers using a combination of the digital output and analog inputs.

Similarly, to test an ADC (analog-to-digital converter) you would use the analog outputs and digital input. Devices containing DSPs (digital signal processors) can be tested using just the digital inputs and output.

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