Sound Quality Measurements

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Tech Note

Measurements vis-à-vis sound quality

At AMR/iFi, we go against the tide to some degree as we tend to

refrain from publishing reams and reams of test data. There are

those who like to pour over pages upon pages of test reports

and get excited seeing 0.003% THD figures or 126dB SNR. We

aren’t in that category.

This is because:

1. Making reliable measurements is not a ‘5 minute job.’ It takes hours if not a full day or two

to properly execute.

2. Processing the raw test data for understandable publication takes even more time.

3. Most importantly, measurements shed little (if any) light on sound quality.

1. Making reliable measurements

As John Atkinson of Stereophile will attest, using an Audio Precision 2 measurement platform is not

trivial. Complex measurements executed on such precise systems are significantly more challenging

than checking DC voltage on a fully automatic multimeter.

Take our previous iPOWER article as an example; while internally

we measure constantly, we don't publish the specs until we have

everything out of the way. To share with an outcome this

specific, it takes at least one full day of proper test rig setup,

calibration and recalibration. It’s as far from just sticking two

probes somewhere and reading the display as it gets. The

takeaway is that the AP2 takes time and effort and then needs

to be checked and re-checked.

2. Processing raw data takes time

Each test or measurement provides more or less precise data but only provides a singular answer to

one very specific question above all else; the Volt DC, THD&N or SNR figures…

Now, measuring DC (ideally under nominal load - which complicates

things) tells one if a power supply operates on the most basic level. It

tells one nothing about how much noise the power supply generates,

which is far more informative. Point being, a basic digital multimeter is

unable to measure the noise of a good quality power supply.

However, the results of many different measurements performed on a device, inform us about the

device’s performance in strictly one specific test. The only conclusion that can be drawn from these

procedures is if the device works as intended within the limits of each test.

Summary of content (5 pages)

PAGE 1
Tech Note Measurements vis-à-vis sound quality At AMR/iFi, we go against the tide to some degree as we tend to refrain from publishing reams and reams of test data. There are those who like to pour over pages upon pages of test reports and get excited seeing 0.003% THD figures or 126dB SNR. We aren’t in that category. This is because: 1. Making reliable measurements is not a ‘5 minute job.’ It takes hours if not a full day or two to properly execute. 2.
PAGE 2
Tech Note any If we aimed for 0.005% THD and 0.05% THD is measured, we know that something is off as the product doesn’t work as intended. Said measurement result is needed in order to seek out the problem and correct it, therefore it is useful in this specific case. Yet what it does not provide is indication of sound quality, none at all. 3.
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Tech Note the 30th harmonic exceeds 0.003% this will be audible and has been shown to be objectionable. So in one case a system with 3% THD at 100dB SPL would pass the ‘no audible distortion’ criteria. While in another case a system with 0.003% THD would not pass the ‘no audible distortion’ criteria! This is of course hardly news, distortion audibility discussions are already known from dawn days of high fidelity in the 1950's. Yet this article provides a summary of the Audio of Distortion Audibility ca.
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Tech Note The next step is in the listening.
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Tech Note The Digital Engine: D1. D2. D3. D4. DAC Power supply upgraded with iFi custom ultra-low noise Operationsverstärker OV2028 DAC reference voltage decoupling changed to Panasonic audio-grade ECPU film capacitors Digital power supplies upgraded with ultra-low impedance Panasonic OSCON capacitors GMT® Femto precision clock system power supply upgraded for super low phase-noise/jitter The Analogue section: A1. A2. A3. A4. A5.