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Audibility thresholds of amp and DAC measurements

DonH56

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Hi Don,

What I actually meant is if your source music being played is recorded at 0 dBFS or close to it (like most pop music). The volume level of the amp would be calibrated to output 96 dB when your source music is recorded at 0 dBFS. Now, 96 dB is very loud, and I usually listen at much lower levels, but I used it for argument's sake.
I am not sure the question, sorry, juggling too many things today. If your DAC adds no distortion, and assuming by "DAC" you mean the actual DAC plus the filters and amplifiers that deliver the analog signal to you rears, then if you set the DAC to full-scale (0 dBFS) and the SPL at your ears is 96 dB then the IMD is at 0 dB -- again assuming no other distortion sources (unlikely). If you turn the DAC down to -30 dBFS the output SPL would be 66 dB and the distortion products will be about 76 dB below that.

The distortion in the recording depends upon the chain up to and including the ADC.

Generally if you turn down the volume the distortion goes down but the noise stays flat thus SNR goes down but THD/IMD improves.
 

daftcombo

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Hi,
What does it mean for an amplifier to have an IMD of 0.05 %?
Bad or ok?
I read somewhere that IMD was worse than THD to the ears.
 

RayDunzl

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sergeauckland

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I
Hi,
What does it mean for an amplifier to have an IMD of 0.05 %?
Bad or ok?
I read somewhere that IMD was worse than THD to the ears.
Harmonic distortion is just that, harmonically related to the fundamental, and so can add to overtones of musical instruments without greatly changing their timbre. As such, not only do we tolerate harmonic distortion, but some even find it pleasing. Something like a violin, or better still, a flute can be thought of as a sine wave generator with a lot of harmonic distortion.

Intermodulation distortion is what happens when two (or more) frequencies modulate each other, and create tones which are not harmonically related to any of the tones. These extra tones are generally thought unpleasant.

However, as HD and IMD are created through the same process, that of non-linearity of the amplifier, one can't have one without the other.
An amplifier with 0.05% IMD will probably have much the same order of magnitude of THD. Whether this is audible or not, depends on many factors, but if 0.05% is a worse case, then nothing to worry about. If a best case, then the reality could be a lot worse and become audible.

S.
 

daftcombo

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Coming back to this thread's first post:

THD, IMD: -66 dBFS / 0.05%
Noise: -85 dBFS / 0.005%
SINAD: 85 dB
If you have an amplifier which meets:
THD, IMD: -66 dBFS / 0.05%
Noise: -85 dBFS / 0.005%

then it won't meet
SINAD: 85 dB.

So there's a problem here. It seems like lenient SINAD doesn't mean anything.
 

flipflop

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If you have an amplifier which meets:
THD, IMD: -66 dBFS / 0.05%
Noise: -85 dBFS / 0.005%

then it won't meet
SINAD: 85 dB.

So there's a problem here. It seems like lenient SINAD doesn't mean anything.
SINAD doesn't mean much to me, which is why it wasn't included in the original draft. I added it later per request.
It's more useful to look and distortion and noise separately when possible.
 

HuskerDu

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This is really, really good info. At the risk of taking the fun out of it, is there a version in Excel somewhere? I want to add a second row for PRICE on everything that meets "strict." Why look at extraneous features on pointlessly expensive gear. Another stack-rank near the "lenient" boundary would also take the "mystique" off the price for perfection, I would think. I'm having a hard time finding a better/dollar DAC than a handful of close-out Chromecast Audio pucks, at $15 each. (But heck, any DAC under $150 is essentially "free" compared to any worthwhile speaker.)

Um, can you do the same "schema" for room noise... :D Puhlllllleeeeeease...? (I'm prepared to help!)

P.S. I've read the room noise I and II posts. (I don't see a third, or I missed external ref...?)
 

flipflop

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At the risk of taking the fun out of it, is there a version in Excel somewhere?
No, I don't have any related content that wasn't included in the opening post.
I want to add a second row for PRICE on everything that meets "strict."
You would have to pick a single measurement then. No device falls below strict thresholds in all of them.
Um, can you do the same "schema" for room noise... :D Puhlllllleeeeeease...? (I'm prepared to help!)
It would have to be for another thread. This one deals with amps and DACs only.
 

daftcombo

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In THD+N vs frequency plots, it's not always possible to tell the distortion and noise apart, so the lenient noise threshold of -85 dBFS / 0.005% THD+N will be used.

View attachment 18973
Behringer doesn't manage to stay below the lenient threshold. The strict threshold is off the chart, so it hasn't been marked.
Hi,
In the text you speak of 0.005%, but in the graph the line is at 0.05%.
 

flipflop

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Hi,
In the text you speak of 0.005%, but in the graph the line is at 0.05%.
Thanks. The text was right, the graphs were wrong. They have now been updated. The first one has also been replaced with a better example.
 

daftcombo

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Thanks. The text was right, the graphs were wrong. They have now been updated. The first one has also been replaced with a better example.
The Behringer would have seemt to be a big piece of crap if you had kept the graph but with the corrected green line!!
 

flipflop

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The Behringer would have seemt to be a big piece of crap if you had kept the graph but with the corrected green line!!
Yeah, but spikes typically indicate distortion, not noise, so I think the Yggdrasil is better for getting the point across :)
 
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Frequency range of human hearing
Humans cannot hear sounds of every frequency. The range of hearing for a healthy young person is 20 to 20,000 hertz.
For the eardrum-targeting headphone use case this should be the end of the story, but I wonder how much relevance it has for listening through bone-conduction headphones (skullphones?) or through speakers that there's some capacity for humans to "hear" things via ultrasonic vibrations, as in https://science.sciencemag.org/content/253/5015/82

Frequency response, channel balance
Going back to NwAvGuy's amp guidelines, he recommends a maximum of 0.5 dB deviation (from 0) in the frequency response.
Psychoacoustics: Facts and Models by Hugo Fastl and Eberhard Zwicker is not a very quotable book, but on pages 180-181 it makes it clear that a change in SPL of less than 0.2 dB can be heard by humans.
In 'Sound Reproduction: The Acoustics and Psychoacoustics of Loudspeakers and Rooms' Floyd Toole says the following: "The simplest deviation from flat is probably a spectral tilt. There is some evidence that we can detect slopes of about 0.1 dB/octave, which translates into a 1 dB tilt from 20 Hz to 20 kHz — not much."
0.1 dB is therefore the strict limit.
Mhhh, not sure the tilt case is measuring the exact same thing though. When I went looking for info on this I found it reported that 0.41 dB is the loudness difference where subjects' guesses on whether they heard a difference or not become no better than chance (could be untrained listeners though, so I could see 0.2 being the right value for trained listeners): https://asa.scitation.org/doi/abs/10.1121/1.1916528

When I tried this myself at 0.5 dB I could guess the difference with a 77% success rate out of 200 tries of 3 choices each (louder, quieter, same), so well over the blind-chance 33%: https://www.audiocheck.net/blindtests_level.php?lvl=0.5
(This was in the silence of night, using the Superlux HD668B.) Don't remember how I did for 0.2, but at 0.1 dB I'm almost sure I was no better than chance no matter how much I tried, so at least for me this threshold is not something that's going to make me spend more money on reproduction equipment. :)

Then again one thing that maybe needs mentioning in the context of any thresholds guide like this is that the more up-stream a device is (particularly if it's before all the amplifiers), the more it has to account for what might happen after it in the chain and perform somewhat beyond the thresholds of hearing just because of the additional degradation that might be introduced downstream.
 
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