Tag Archive for: mp3

MP3 Player (Multitone) Sequence

The principle is first to create a multitone stimulus waveform with SoundCheck and transfer it to the MP3 Player to be tested. This waveform is then played back, to be acquired and analyzed by SoundCheck. Both Left and Right channels are acquired at once. The acquisition is made easy by using a trigger on one input channel. The analysis is done by comparing the genuine stimulus and the play-back, using a cross-spectrum technique that provides the FRF, Cross-talk and Non-Coherent Distortion. The cross-talk between channels is measured by playing simultaneously two different multitones for Left and Right channels with interleaved frequencies, and making a cross-analysis between channels (e.g. finding in the right response the contribution of the left stimulus).

Due to inaccuracies of clock frequency, the play-back sampling rate is often different from the Soundcard recording sampling rate. Therefore, in SoundCheck, the recorded time Waveforms are frequency shifted as to obtain a perfect match between stimulus and responses. This frequency correction is performed on both channels before the Analysis steps. The exact playback sampling rate is displayed. The Sequence can be measure the MP3 player on the WAV or the MP3 file playback. The MP3 playback will yield a poorer FRF and more distortion, due to the lossy compression.


Triggered Record Using WAV File (Version 16.0 and earlier)

triggered_record_screenshotThis sequence allows you to test devices without an analog input such as tablets, cellphones and MP3 players. A stimulus WAV file is created in SoundCheck, and copied to the device under test, where it is played and the response recorded in SoundCheck as if the stimulus were played directly from SoundCheck. The stimulus WAV file to be used on the device under test (DUT) may be customized in the stimulus step.

Note that this sequence uses the level-based trigger available in SoundCheck 16.0 and earlier. If you are using version 16.1 or later, please see the frequency-trigger based sequence which takes advantage of new functionality to offer more robust triggering.


Challenges of MP3 Player Testing

MP3 player audio performance is discussed including measurements of frequency response, phase response, crosstalk, distortion, sampling rate errors, jitter, and maximum sound pressure level with headphones. In order to make these measurements, several measurement techniques and algorithms are presented to overcome some of the challenges of testing MP3 players. We discuss test equipment requirements, selection of test signals and the effects of the encoding on these test signals. A new method for measuring non-coherent distortion using any test signal including music is also presented.

Authors: Steve Temme, Pascal Brunet and Zachary Rimkunas
Presented at the 122nd AES Convention, Vienna, 2007

Full Paper

The Challenges of MP3 Player Testing

Author: Steve Temme

MP3 players have been the ‘must-have’ electronic gadget for the past few years. Over 10 million players were sold in 2005, and this is predicted to rise to more than double this by 2010. But how can manufacturers carry out QA tests on the production line, ensure excellent sound quality and demonstrate their compliance with Sound Pressure Level regulations? MP3 player testing is challenging as it combines traditional audio analysis techniques with some characteristics unique to MP3 players. Here, we examine the equipment and techniques that MP3 player manufacturers can use to test the sound quality of their products, and advise how to overcome some of the challenges inherent to measuring MP3 players.
Full Article