Get familiar with measuring the frequency response of sound

Measuring the same value twice in a row is difficult

In our tests, you will increasingly encounter measurements of the “frequency response” of the sound of PC components. These are useful and rare measurements. As one of our readers has pointed out – for those who can read spectrographs, they are a gem. It’s worse if you don’t understand them. Then they won’t tell you much, and that’s a shame if you also care about the exact “noise” value of computer components, or their sound expression.

Measuring the same value twice in a row is difficult

If you hold your breath while measuring the noise level with a standard sound level meter, you’ll go crazy when measuring the frequency response. It is not at all easy to measure the same values of the same sound repeatedly. Purposely choose a constant sound source and record its frequency response several times during the day. All you need is a regular microphone and one octave, which is available in the free version of TrueRTA (you can download it here).

You can’t easily get completely identical graphs across measurements, and we were frustrated by that too. However, with the help of various gimmicks, we reached a very small, negligible measurement error, which fits below 2%. It is important to create completely identical conditions here, in which only the sound of the measured device changes. Around the test rig, we had to place acoustic panels from three sides (from the sides and above), which prevent the sound from bouncing differently into the microphone sensor. Whether the sound from the measured device or from the room. After all, it is quite uncomfortable to commit that nothing will change in the testlab dispositionally just because it would have a negative effect on the accuracy of the measurements.

There is then a parabola-shaped collar around the sensor, one of the tasks of which is to amplify the measured values. This makes it possible to distinguish even really quiet frequencies and also so that the spurious tones coming from behind are bounced outside the sensor. Thus, for example, the breathing, which I unfortunately cannot avoid, is possible to filter out in this way.

The same mutual distances of the microphone from the measured device, the scanning angle (15°) are always important, too. We always set the angle exactly with the inclinometer. The fixed distance is indicated by the marks for the tripod legs.

Of course, the key is to filter out all spurious frequencies that do not relate to the device being measured (such as a graphics card), so this requires passive operation of other components, while the results may be distorted by whistling coils on the motherboard or the power supply. However, we managed to eliminate all this. We will also state the intensity of the dominant frequencies. Again, in three bandwidths of low (20–200 Hz), mid (201–2,000 Hz) and high (2,001–20,000 Hz) tones. The last test of graphics cards already includes this methodology and new results will snowball with each new test.

Maybe you are interested in one more thing that has not been said in the text so far. Namely, at which point we read the values that are inserted into the tables. Of course, the noise level of graphics cards changes over time according to the load. Therefore, the measured values are based on the average of the last 100 samples, which have a more or less stable form. We always read this data just before the end of the test scenes in games F1 2020, Shadow of the Tomb Raider, CS:GO and apps Blender (Cycles), Classroom. Then the fan speed is already stable and no longer increases.

So ladies and gentlemen, don’t believe in one value measured by a sound level meter so much. It’s enough for a rough orientation and an idea of how noisy a particular component is, but you will have to study its frequency analysis for accurate sound. However, you will receive all the materials for studying these properties from us. Even in the tests of coolers and measurement of the frequency response of sound, you will of course soon find in in the fan tests, which we can no longer wait for ourselves and we believe that you feel the same way.

I apologize for the potential inaccuracy of expression and incorrect terminology or imperfect technical implementation of some aspects to all sound engineers and people more erudite in acoustics than I am (I certainly do not consider myself a sound master 🙂 ). The aim of this all was to achieve the highest possible sound distinction and satisfactory repeatability of measurements with the least possible error. In addition, it was all aimed at ensuring that the results were of relevant quality, which was successful.

• Contents
• How to read spectrographs and tables correctly
• Measuring the same value twice in a row is difficult