E-Mu 1212M Soundcard Tests 

Introduction

It is always important to have as good a reference for ones test measurements as possible. This is why HP (Aligent) and others sell us nice shiny big boxes with calibration certificates traceable to national and international standards.

Sometimes it is necessary to use slightly more modest setups and it is useful to make some base line tests to gain a series of measurements to relate to when interpreting "live" test results. It is after all no use chasing amplifier distortions of less than 0.001% THD if the measurement system itself isn't able to better that performance.

The following measurements were made with my current PC based soundcard setup. I now test 20 Hz to 96 kHz, although these tests are from 45 Hz upwards. Below 20 Hz it is better to use 4 million point FFTs, and 16 million if one wishes to go sub 1 Hz with any fine detail.

Even with the obvious limitations of the PC based measurement system looking at the BIG PICTURE enables one to see low level detail that is not apparent in much of the published audio test results. Typical of a "standard" test is a 100dB range maximum (relative to the signal peak, not absolute) and a bandwidth from 1kHz to 20 kHz. The following image illustrates the very small window through which those tests are looking.

Comparison between 45 Hz to 96 kHz and 1 kHz to 20 kHz range FFT tests.

Although not very apparent in these loop-back tests many if not most of my amplifier tests have both 50 Hz mains and 20+ kHz EMC/RFI from switching power supplies/monitors showing. This is the nature of bench testing and I deliberately leave these in to show the whole story.

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Test Setup

24 bit - 192 kHz - 1 Million Point FFT Open circuit or loop-back tests, balanced output to balanced input. Twin + screen low noise microphone cable with Neutrik XLR connectors. Levels and results as per WINaudioMLS software. Images are 957 pixels wide for clarity.

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