MP3 Player Testing

The dScope Series III is ideally suited to mass production testing of MP3 player audio performance and is in use for this application around the world. There are probably as many ways to test an MP3 player as there are MP3 player manufacturers. There are, however, trends that are almost universal: most MP3 players do not have audio inputs, and instead rely on a computer interface (usually USB) to load the audio.

Most MP3 players are mass production, low margin items, where speed is absolutely critical. This has lots of ramifications for testing: the audio test file must be short, since it must be loaded onto the device in production, and several measurements must be taken quickly – simultaneously if possible.

At its simplest, an MP3 test involves loading a test signal into the MP3 player, and playing it back into the dScope’s inputs. For basic tests, a single signal is sufficient, since the dScope can use its multi-tone capability, together with its FFT Detectors, to allow analysis of several audio parameters simultaneously (for example frequency response, THD+N and cross-talk). For more complicated tests, the track can consist of different sections, all of which the dScope can detect automatically when a script is used to automate the tests.

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Since the playback rate is determined by the MP3 player (and not the dScope’s Generator) it is not possible to use synchronous multi-tones, so FFT Window functions must be used. The MP3 processing produces noise “skirts” on the tones which must be taken into consideration, particularly when measuring cross-talk. In this scenario, a single file is loaded into the MP3 player, its outputs connected to the dScope, and the file played back. The dScope can be programmed to detect the file playback, make a quick measurement, indicate pass or fail, and log the results. This could be done in as little as 2 seconds, meaning that an MP3 file lasting around 3 to 4 seconds is sufficient.

For more sophisticated tests, more stages of the test tone are required. This adds its own complications as the test must now be able to detect where one section of the test ends and the next begins. Fortunately, with dScope scripting, this is not too difficult. The automated solution can easily detect a change in the signal coming from the MP3 player, thus allowing the next section of the test to start automatically. Failure to detect the new signal, or failure of any part of the test, can be programmed to ask the user for a retest if required.

An example script with documentation is available for download from the dScope Scripting page.

For more information please contact us using our Enquiry Form.