AP - The Recognized Standard In Audio Test


High quality portable digital audio recorders are proliferating, with better and more affordable models constantly being introduced. These recorders are characterized by the ability to record high quality uncompressed audio, with some models matching or exceeding the quality of studio equipment. In the film and television industries, they replace the venerable open-reel Nagra and professional DAT recorders. In the radio news and nature sound recording fields, they replace portable cassette, DAT, and MiniDisc recorders. Portable recorders are used in a multitude of other fields, including music recording, acoustics, research, museum and event soundscapes, nature sounds recording, interviews, and more. Prices currently range from about $200 to $20,000, depending on the feature set, quality level, and intended market.

Fully characterizing the audio performance of these devices requires an involved series of tests in both the analog and digital domains. Furthermore, because many of these recorders are state-of-the-art devices with 24 bit 192 kHz converters and extremely quiet microphone preamps, high quality audio analyzers, like Audio Precision's 2700 Series, APx500 Series, or ATS-2, are necessary to obtain meaningful results.

Common Challenges

  • The microphone preamp in a digital recorder must undergo a series of comprehensive tests, just like a stand-alone mic preamp. How does it perform with attenuators and filters engaged, with phantom power turned on, and with extremely loud or soft signals? The Audio Precision 2700 Series and the APx 500 Series are ideally suited for measuring these extremely sensitive signals.
  • High quality headphone outputs are essential so that the recordist can monitor the recording quality and make fine adjustments. Can the outputs supply sufficient volume to a variety of commonly used professional headphones while maintaining flat frequency response and low distortion? For a comprehensive test, use one channel of the analyzer to monitor power output and distortion, while connecting the other channel to an acoustic coupler to measure headphone volume.
  • Audio recorders frequently are used for sound acquisition, with playback performed on another device or computer workstation. Therefore, it is often necessary to inject an analog signal and test the output in the digital domain. Likewise, to test the analog playback chain, it is necessary to load digital files onto the recorder and test their output.
  • For multi-track digital recorders, Audio Precision offers a variety of solutions. The new APx 500 Series has 8 or 16 input channels (APx585/APx586) and 8 output channels, for the fastest testing of multichannel devices. The 2700 Series 2-channel audio analyzers, in combination with the SWR-2755 switchers, offer state-of-the-art performance. Not only is multiple channel testing useful for multi-track devices, but it speeds testing of the multiple inputs and outputs on stereo devices (microphone in, line in, main out, headphone out, foldback monitor etc.), enabling automated testing without cable switching.

Tips for Optimum Testing

  • Test at a variety of sample rates and bit rates, both compressed and uncompressed.
  • Test with the recorder actually recording, so that any noise generated by hard disks and other components will be replicated. Turn on the display backlight to check for interference, and turn up the headphones.
  • Analyze both the direct digital output of the unit, and the output from its recorded wav files, and see if they are the same. They should be, but sometimes they aren't.
  • When testing the microphone preamp on a recorder, concepts like gain and output voltage don't have the same meaning that they do with a stand-alone preamp.

Back To Top