Why you can't trust measurements

[yamamoto2002]

Measurement is useful to find and fix design defect of the product.  Sometimes the result tells is not related to perceived sound quality. Sometimes it tells sound degradation overlooked and it can be heard by ears on specific corner-case condition or just by changing framing of the cognition.

 

When I show the measurement result, I tried to create champion data, to minimize mains and computer interference, prevent the click noise of fluorescent lamp or microwave oven switching during measurement etc. In Japan, mains earthing system is TT, wall outlet is 2 prong and isolation transformers for domestic market works well to prevent ground loops 🙂 Recent addition is metal wire mesh bag for measurement laptop, to reduce unwanted Wi-Fi interference or outgoing noise radiation.

 

 

[yamamoto2002]

In Japan, a Ferrari dealer (Cornes and co. ltd) sells Audio Precision products🙂

[yamamoto2002]

It is not possible to rely on my ears fully to test audio equipment or audio app because I cannot hear some noise.

 

Younger people's ears have better frequency range (they hear mouse repellent, elevator power converter noise, fluorescent lamp noise, car brake pad squeal: it squeals every time when brakes and its frequency lowered when pad worn, SMPS acoustic noise, NTSC flyback transformer noise of old recordings) and better dynamic range (they hear mosquito sound in 3 meter distance, -10dB SPL and complains constant hiss or intermittent hiss (it seems the noise stops when amplifier power saving is activated) from loudspeakers)

[yamamoto2002]

I watched the video 🙂 Thank you for sharing.

 

From the observation, it seems AP analyzers are less susceptible to ground loop problem and its DAC measurement result is relatively consistent and reliable. On the gaming PC review sites, RMAA is still mainly used to measure onboard DAC quality. RMAA itself is excellent app but people use it with too carelessly and their measurement result is totally unreliable, there is a 15dB to 20dB SNR discrepancy on the same onboard DAC, almost always contaminated with ground loop problems, sometimes it seems measurement is simply failed with accidental click noise or other issues.

 

From 16:45 of your video, there is some solution to measurement setup problem presented. With RMAA and off the shelf audio interface, additional care is needed to get more consistent and meaningful results. I learned inexpensive but adequate measurement method from an local DIY amp builder magazine articles, but it seems the knowledge is not shared enough and/or gaming PC reviewers do not have enough curiosity for audio measurement.

 

About intersample overs, I read somewhere, some oversampler of earlier DAC has no tolerance and waveform is flipped by integer arithmetic overflow!

 

Here is my RMAA result of Asus Z370i onboard Realtek S1220A DAC. I think it is excellent DAC but on the internet, there are 15dB to 25dB worse RMAA results circulated 😱

 

 

 

 

 

 

 

 

 

 

[yamamoto2002]

The video states a variation of measurement test vector is insufficient and big SQ deterioration or noise is sometimes overlooked. I agree about it. Personally, I'd like to see coil/MLCC whine acoustic high-pitched noise spectrum test of laptop PC and computer monitors to find suitable gears for high resolution recording. Also it is nice to have LPS power transformer rumble noise test caused by DC offset added AC mains power (some household in Japan has this problem). DAC click noise level test when sample rate is changed or mute is activated/deactivated or PCM/DSD mode change.

[yamamoto2002]

1 hour ago, GoldenOne said:

If you use RMAA with an ADI-2 Pro FS R for example like Archimago (or myself prior to getting the APx555) then you can get very good results.
If you just use a basic focusrite interface then you're not gonna have such a good time.

 

From my experience, self powered ADC is more problematic than bus powered USB/firewire ADC. For example, Babyface Pro or bus powered Fireface 400 is easier to use than Fireface UC or ADI-2 Pro

 

1 hour ago, GoldenOne said:

I saw this actually but can't remember for the life of me what DAC it was. I think it might have been an earlier denafrips DAC?

 

 I don't remember correctly but some early portable CD player have this problem, and content with intersample overs sounds very differently with such device. IMO it is better for every DAC to produce loud noise and bright red lamp is lit when intersample over happens, because it is defect of music content that should be found and fixed before delivery. Intersample overs resemble to bugged software that cause undefined behavior.

[yamamoto2002]

6 hours ago, fas42 said:

Yes, I'm aiming for a googolplex - at least ...

 

It seems relatively small number of bits are needed to express 1 googolplex with PCM digital 🙂

 

33219280948873623478703194294893901758648313930245806120547563958159347766086252158501397433593701550996573718 + 1 bit (extra one bit is for sign bit)

 

BTW number of atoms of the earth is approx. 10^49 to 10^50, so it is not possible to build the storage to store this data.

 

 

 

 

[yamamoto2002]

I looked into further and now I think symbolic math approach is better to accommodate such a big numbers, i.e. 1 googolplex is expressed as a string of "10^{10^{100}}" as a sampled value of PCM: On this approach, 1 googolplex number occupies only 13 bytes on the storage, and much larger values than 1 googolplex can be expressed (Fig.1). Furthermore, there is no quantization error on rational, irrational and complex numbers such as "{-1+i√3)/2" which is e^{i*π/3} = cos(π/3) + i*sin(π/3) because there is no quantization performed, and any sinusoidal waves can be expressed mathematically exact.

 

Fig.1