[Atriya]

So, I understand that loudness is supposed to be the only thing that power dictates, not other characteristics of the sound.

However, here's something I tried:

I took my 32ohm-impedance/94db-mW-senstivity headphones (Hifiman Arya SE) and drove them directly from the 1Vrms output of a DAC (Chord Qutest, which has very low output impedance). The calculated volume is 108.9db.

Then I drove the same headphones setting the same DAC to output 3Vrms. The calculated volume is 118.5db. But, upstream from the DAC, in software, I attenuated the signal by the difference in volume - I had to use 10db instead of 9.6db - resulting in a volume of 108.5db.

With this (close) volume matching done, the second setup, which puts 282 mW into the headphones instead of 31mW in the first setup, clearly had a greater depth of soundstage.

What could be going on here?


A note about the software attenuation: It was done in HQPlayer using 15th-order noise-shaping (LNS15), while upsampling to 768Khz. My understanding is that this is about as transparent as software attenuation gets. And in any case, it was the version with the software attenuation that displayed the deeper soundstage.

 

[AudioThief]

With this (close) volume matching done, the second setup, which puts 282 mW into the headphones instead of 31mW in the first setup, clearly had a greater depth of soundstage.

What could be going on here?

Most likely: Your biases impacts the way you perceive the sound, making you believe there is a difference in sound stage when there in fact is not.

 

[gregorio]

So, understand that loudness is supposed to be the only thing that power dictates, not other characteristics of the sound.

We can’t “understand that” because it’s not true. Loudness is not a characteristic of sound, it’s a characteristic of human perception and power does not dictate loudness, it just dictates the output level, which may or may not be perceived as louder/quieter depending on other variables.

With this (close) volume matching done, the second setup, which puts 282 mW into the headphones instead of 31mW in the first setup, clearly had a greater depth of soundstage.

That’s not volume matching. Sure, a 0.4dB difference is obviously more closely matched than say a 3dB difference but one of the conditions of scientific acceptance of the results of listening tests is matching to 0.1dB or lower. Because higher than 0.1dB can artificially affect the results.

What could be going on here?

It might be a failure to volume match properly but could be a number of other things. Most likely a perceptual error caused by an inappropriate methodology (that failed to eliminate biases) but it could be a faulty assumption about the impedance.

A note about the software attenuation: It was done in HQPlayer using 15th-order noise-shaping (LNS15), while upsampling to 768Khz. My understanding is that this is about as transparent as software attenuation gets.

That depends on what you mean by “transparent”. The most transparent that software attenuation gets is simply to lower the output level and not to upsample and noise-shape as well. However, assuming the HQPlayer isn’t doing something silly (which is possible) then the process you describe should not be audibly less transparent. As a general rule, it’s better to avoid this type of software player upsampling and processing.

G

 

[Atriya]

We can’t “understand that” because it’s not true. Loudness is not a characteristic of sound, it’s a characteristic of human perception and power does not dictate loudness, it just dictates the output level, which may or may not be perceived as louder/quieter depending on other variables.

A quick note that I meant to type "So, I understand that loudness is supposed to be..." and mistakenly left out the "I".

So, I was not trying to convince you of anything, but was just articulating my own current understanding.

 

[gregorio]

I was not trying to convince you of anything, but was just articulating my own current understanding.

Ah, OK. Unfortunately though, there are some holes in your current understanding. That’s normal of course, no one is born with understanding, plus there’s the added difficulty that the audiophile community and it’s marketing often tries to obscure it!

Small differences in level are typically not perceived as a difference in loudness, they’re typically perceived as the same loudness but as some other difference in quality (which could include soundstage). This fact underpins the existence of the “loudness war”.

However, there’s no way of knowing if this is the case in this instance, there may be some other perceptual error at play. Some ABX testing would reveal if there is an audible difference and could reveal what it is.

G

 

[71 dB]

I took my 32ohm-impedance/94db-mW-senstivity headphones (Hifiman Arya SE) and drove them directly from the 1Vrms output of a DAC (Chord Qutest, which has very low output impedance). The calculated volume is 108.9db.

So you drove your headphones from the RCA analog outputs? I did not find any information about the output impedance (on the product pages) so how do you know it is "very low"? Is it below 1 ohm? 10 ohm? 100 ohm? Typical output impedance for RCA outputs is 100-1000 ohm. Also, are you sure the voltage level selection doesn't change the output impedance? It is possible the DAC uses 3Vrms output all the time, but resistors (voltage dividers) are used to select output voltage level meaning the impedance changes.

 

[Atriya]

So you drove your headphones from the RCA analog outputs? I did not find any information about the output impedance (on the product pages) so how do you know it is "very low"? Is it below 1 ohm? 10 ohm? 100 ohm? Typical output impedance for RCA outputs is 100-1000 ohm. Also, are you sure the voltage level selection doesn't change the output impedance? It is possible the DAC uses 3Vrms output all the time, but resistors (voltage dividers) are used to select output voltage level meaning the impedance changes.

All good points.

Yes, I drove my headphones directly from the RCA analog outputs of the Chord Qutest, as has been tried and reported on by many people on the Qutest thread here.

Many online listings state the output impedance to be 0.025Ω, such as this one:
https://www.moon-audio.com/chord-qutest-dac.html
It appears to be a spec that used to be on the official website/manual, but was deleted for some reason.

More concretely, this review measures it to be 0.4Ω at 3V:
https://www.stereophile.com/content/chord-electronics-qutest-da-processor-measurements

As for the voltage level selection, the designer (Rob Watts) has stated on the Qutest thread here on head-fi that it is done digitally in his FPGA.

 

[71 dB]

All good points.

Yes, I drove my headphones directly from the RCA analog outputs of the Chord Qutest, as has been tried and reported on by many people on the Qutest thread here.

Many online listings state the output impedance to be 0.025Ω, such as this one:
https://www.moon-audio.com/chord-qutest-dac.html
It appears to be a spec that used to be on the official website/manual, but was deleted for some reason.

More concretely, this review measures it to be 0.4Ω at 3V:
https://www.stereophile.com/content/chord-electronics-qutest-da-processor-measurements

The review says:

(Except where indicated, all the measurements were taken with the maximum output level set to 3V.)
The output impedance was an extraordinarily low 0.4 ohm at 20Hz and 1kHz, rising to 0.9 ohm at 20kHz,...​

As for the voltage level selection, the designer (Rob Watts) has stated on the Qutest thread here on head-fi that it is done digitally in his FPGA.

Doesn't tell much. Someone should measure the output impedance when the maximum output level is set to 1 and 2 volts.

In this arrangement the 3 V output impedance is less than 1 Ω, but for 1 and 2 volts the output impedance is about 2R/3 meaning if R = 120 Ω, the output impedance is about 80 Ω.

 

[megabigeye]

So, I understand that loudness is supposed to be the only thing that power dictates, not other characteristics of the sound.

However, here's something I tried:

I took my 32ohm-impedance/94db-mW-senstivity headphones (Hifiman Arya SE) and drove them directly from the 1Vrms output of a DAC (Chord Qutest, which has very low output impedance). The calculated volume is 108.9db.

Then I drove the same headphones setting the same DAC to output 3Vrms. The calculated volume is 118.5db. But, upstream from the DAC, in software, I attenuated the signal by the difference in volume - I had to use 10db instead of 9.6db - resulting in a volume of 108.5db.

With this (close) volume matching done, the second setup, which puts 282 mW into the headphones instead of 31mW in the first setup, clearly had a greater depth of soundstage.

What could be going on here?


A note about the software attenuation: It was done in HQPlayer using 15th-order noise-shaping (LNS15), while upsampling to 768Khz. My understanding is that this is about as transparent as software attenuation gets. And in any case, it was the version with the software attenuation that displayed the deeper soundstage.

Sorry I ghosted on your previous thread. I didn't want to discuss ABX tests, or biases, or level matching, or otherwise get too science-y for the rest of Head-Fi (and didn't want to get in over my head with stuff I don't actually know). I'm glad you asked this here— there are some knowledgable people in the Sound Science forum.

I like Gregorio's use of "output level" instead of "loudness". A bit more accurate.

 

[Atriya]

The review says:

(Except where indicated, all the measurements were taken with the maximum output level set to 3V.)
The output impedance was an extraordinarily low 0.4 ohm at 20Hz and 1kHz, rising to 0.9 ohm at 20kHz,...​

Doesn't tell much. Someone should measure the output impedance when the maximum output level is set to 1 and 2 volts.


In this arrangement the 3 V output impedance is less than 1 Ω, but for 1 and 2 volts the output impedance is about 2R/3 meaning if R = 120 Ω, the output impedance is about 80 Ω.

I understand, but, going back my initial two test-cases: in both the cases, where max voltage is set to 1V and 3V resp., I have now learnt that the output voltage is 1V, since in the 3V case I'm digitally attenuating the signal by the calculated amount to drop the output voltage to 1V.

As a result, even if the output impedance at 1V is indeed 80Ω, that wouldn't explain any differences I'm hearing between the two cases, or so it seems to me. Or am I misunderstanding?

 

[71 dB]

I understand, but, going back my initial two test-cases: in both the cases, where max voltage is set to 1V and 3V resp., I have now learnt that the output voltage is 1V, since in the 3V case I'm digitally attenuating the signal by the calculated amount to drop the output voltage to 1V.

As a result, even if the output impedance at 1V is indeed 80Ω, that wouldn't explain any differences I'm hearing between the two cases, or so it seems to me. Or am I misunderstanding?

We don't know what the impedance is at 1 and 2 volts settings, but if the device is constructed in a way I am suggesting, it may have huge effect on sound! 80 Ω is a lot for driving headphones, especially low impedance headphones like 32 Ω. Especially open headphones need typically very low amp output impedance for electronic damping. So, the sound might be less controlled and more distorted with 80 Ω output impedance compared to less than 1 Ω impedance.

 

[Atriya]

We don't know what the impedance is at 1 and 2 volts settings, but if the device is constructed in a way I am suggesting, it may have huge effect on sound! 80 Ω is a lot for driving headphones, especially low impedance headphones like 32 Ω. Especially open headphones need typically very low amp output impedance for electronic damping. So, the sound might be less controlled and more distorted with 80 Ω output impedance compared to less than 1 Ω impedance.

I understand this. All I'm saying is that whatever detrimental effect the higher output impedance has, it should apply to both cases, since in both cases the effective output voltage is 1V, and therefore should not contribute to hearing differences between the two cases.

 

[71 dB]

I understand this. All I'm saying is that whatever detrimental effect the higher output impedance has, it should apply to both cases, since in both cases the effective output voltage is 1V, and therefore should not contribute to hearing differences between the two cases.

I beg to differ. The "effective" voltage doesn't really matter. You shouldn't go near it (hearing damage, distortion etc.) You want your peaks be 100 dB or less. That's 4 mW of power at 94 dB/mW sensitivity or 0.36 Vrms.

Anyway, this is useless, because we don't know all the facts. All I can say use 3 V settng if that gives the best sound, or better yet, buy a proper headphone amp, because driving your headphones from the RCA outputs of a DAC sounds crazy to me.

 

[Atriya]

I beg to differ. The "effective" voltage doesn't really matter. You shouldn't go near it (hearing damage, distortion etc.) You want your peaks be 100 dB or less. That's 4 mW of power at 94 dB/mW sensitivity or 0.36 Vrms.

Anyway, this is useless, because we don't know all the facts. All I can say use 3 V settng if that gives the best sound, or better yet, buy a proper headphone amp, because driving your headphones from the RCA outputs of a DAC sounds crazy to me.

I do have an amp actually. A very powerful one: Burson Soloist 3XP. I discovered this direct drive from RCA thing only recently, and found it to have a clearer sound than using the Burson, like a veil being lifted.

 

[gregorio]

All I'm saying is that whatever detrimental effect the higher output impedance has, it should apply to both cases, since in both cases the effective output voltage is 1V, …

This appears to be your misunderstanding. It won’t necessarily “apply to both cases”! It could depend on how you get to that 1V output voltage. For example, driving a 3V output stage with a digitally attenuated signal (to achieve 1V) or driving a 1V output stage with less or no digital attenuation. In the 2nd example, the analogue circuitry reducing the output to 1V could also be significantly raising the impedance, circuitry that isn’t in the 3V output stage. Therefore this significantly higher impedance does not “apply in both cases”, it would only apply in the 2nd case and could make an audible difference with HPs requiring a lower impedance.

This is what @71 dB was trying to explain.

G