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The latest update to Audio Precision’s APx audio analysers (v2.3) allows the accurate measurement of the error rate in a device passing audio in lossy formats such as Dolby or dts.

Every device that passes digital audio strives to be bit-accurate – that is, to pass the digital audio stream unchanged from its input to its output.

However, devices may unintentionally truncate data, introduce dither, scale the signal, or convert the sample rate.

These errors may be hard to detect with a traditional THD+N measurement, but they can cause havoc for devices receiving the corrupted data later in the signal path.

Most audio analysers can already measure in so-called ‘bitstream mode’ to ascertain that digital audio is passed through a device without corruption.

However, there has been no way to test lossy encoded audio formats such as Dolby and dts.

Audio Precision’s technique, introduced with the v2.3 update for APx Series audio analysers, allows both lossless and lossy streams to be tested.

This is essential in accurately evaluating whether an HDMI source can properly handle all the different formats that may be requested by an HDMI sink.

APx calculates the digital error rate by measuring a proprietary waveform with a deterministic relationship between samples.

This allows the instrument to detect any errors in the output of a digital device on a sample-by-sample basis.

The algorithm used is generator-independent and allows the instrument to test closed-loop digital devices (such as routers and switchers) as well as playback devices including CD and DVD players.

Using specially defined test signals, it is possible to determine the digital error rate of playback devices outputting Dolby- and dts-encoded signals.

APx instruments can generate the test signal from any digital output, including SPDIF, Toslink, HDMI, and Audio Precision’s Digital Serial I/O interface.

In addition, the test signal is provided as WAV, AC3 (Dolby 5.1), DTS (dts-encoded 5.1 audio), and DTSHD (DTS-HD Master Audio) files.

CD audio and DVD test discs are also available.

The digital error measurement can also be used to test bit-for-bit accuracy over time (to over 10,000 minutes), a useful feature for detecting intermittent errors that would otherwise be hard to reproduce.

Available views of the data include average error rate, instantaneous error rate, total errors and cumulative errors over time.

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