Investigation Into Effects Of PC load On DAC Analogue Output

[semente]

Since these measurements don’t show the effects of “PC load”, which other measurements could be performed?

Peter has already suggested multi-tone IMD. Anything else?

[semente]

6 hours ago, idiot_savant said:

So, we assume that the “noise”  is electrical rather than acoustic, and look for it influencing the output of a DAC on a non-tweaked system. And can’t find it.

We can't find noise at the DAC's ouput.

Ideally we would be testing the D/A chip's performance with different software, OS, computers, input interfaces, etc. but it is easier to just measure the (whole) DAC.

 

Is there a way to measure noise just before the signal goes into the D/A chip?

[semente]

1 minute ago, March Audio said:

You can look at the i2s lines but it's what comes out of the dac that is important.  If there are issues it will be seen in the dac output.

 

I will be trying several different PCs and laptops as sources.

 

I understand what you are trying to say but it has been claimed often that noise "travelling along" with the signal stream affects the D/A conversion.

Could there be an aspect of the D/A chip performance that is not shown in a "traditional" set of DAC output measurements?

[semente]

In other words, is anything not being measured that could explain the perceived audible differences?

[semente]

6 minutes ago, March Audio said:

What youvare really asking here is are there things we can't measure but can hear?

 

Simple answers no.  We can measure way below thresholds of hearing.  However you need to use the correct measurement to find what you are looking for.  Correlation can be difficult. 

 

If I remember correctly people were reporting poor sound quality from early solid state amplifiers and engineers said it wasn't possible. And were later proved wrong (Otala et al.).

Could a similar thing be happening here?

 

You provide a set of measurements that does not explain many reports of perceived audible differences.

Isn't there a chance that something else might need looking into / measuring?

 

I don't have a horse in this race, I am merely curious.

[semente]

19 hours ago, March Audio said:

Actually you might be interested in the paper below which shows those conclusions about negative feedback were wrong.

 

https://www.google.com/url?sa=t&source=web&rct=j&url=https://linearaudio.net/sites/linearaudio.net/files/volume1bp.pdf&ved=2ahUKEwjp3IWGvZLxAhW6wjgGHbMSA4gQFjAAegQIBBAC&usg=AOvVaw3TQHX7dKj3pUiCoPCahlPA&cshid=1623514050065

 

Controlled subjective listening tests are the next step and I am planning to do that.

 

I had read that paper before. It says that:

 

"If there is a relationship, it has to be through the behaviour of the specific circuit implementation. For a given GBW, slew rate is a fixed quantity and slew induced distortion can be predicted exactly from the ratio of actual to maximum slew rate. Nothing will reduce SID other than improving slew rate unless we modify the circuit."

 

I don't see any discrepancy between perceived audible distortion and engineers not wishing to believe it.

[semente]

9 minutes ago, March Audio said:

The blame was put at the door of negative feedback which is not correct.

 

So the Putzeys is correcting Otala. But does he deny TIM audibility and engineers not wishing to believe there was something wrong?

[semente]

Is this of any relevance?

 

Perception of mid frequency and high frequency intermodulation distortion in loudspeakers, and its relationship to high-definition audio.

 

 

 

Griesinger_IMD-perception.ppt

[semente]

On 8/29/2021 at 9:05 AM, Blackmorec said:

My ‘observation’ was that, based on the experiment under discussion, it didn’t appear that the CPU activity level was modulating noise at the DAC’s analog output

What bandwidth are you referring to?

[semente]

2 hours ago, manisandher said:

Including my being able to hear the keyboard strokes through two closed doors and a corridor, and being able to decipher the software settings from them.

The ultimate golden ear test. ABtwo closed doors and a corridor