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General debate thread about audio measurements

NorthSky

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RayDunzl

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Go buy a Fisher Price one for five bucks on eBay

I used a couple of 10k potentiometers between the CD player and power amp for a long time.


1536352808485.png


Cost about $5 for connectors and scrap cable and the pots and a piece of wood and some scrap metal to mount the pots.

I thought it was just fine, still would.
 
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RayDunzl

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Why don't you use them anymore, Ray; you found better ones, cuter, less noisy, ...?

It still in use, in another room.

Because I wanted additional functionality to comfortably accommodate hardware sources and destinations beyond a single CD player and power amplifier?

1536361615093.png


What noise?

A meter of cable with a resistor divider (pot) operating at line levels doesn't provide much opportunity for noise pollution at audio frequencies.
 

NorthSky

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Alright, how loud are we listening to, where on that dial are we turning up that volume control knob (potentiometer, volume attenuator)? How much break pedal (attenuation) are we releasing? What resistance is applied say when we are using normal power...less than 3 watts RMS? @ what average level are we listening to our music? What is the meter showing...0.3 watts? ...Little bit more...1.0 watts? It depends, passive or active listening...background music or front end serious music.
...From a normal stereo preamp, from a headphone amp.


@ low volume level listening we usually measure larger amount of THD.
And the more we crank the volume up the distortion level decreases, up to the power amp limit, where the distortion rises abruptly and clips.
With a quality amp the level of THD is low from 0.001 watts to say 5 watts.
Some amps have larger level of THD @ very low power...say less than 3 watts.

Using a quality amp, how much influence a volume pot can have on the sound output...measurable distortion level? Are there better potentiometers with less measured distortion, and if yes, what are the best ones and why are they measuring better?
 
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RayDunzl

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Alright, how loud are we listening

Right now?

TV News through the little JBLs.

1536365593880.png


The maximum measured peak using the mains was 116.9dB on a short snippet of drums (just testing). Sounded dangerous to me.
 

Wombat

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Rrrrrrrrrrr
Go buy a Fisher Price one for five bucks on eBay. :p

Post #391 above is all that is needed. Put in a box it should sell for somewhat less than $50.
 

RayDunzl

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Ray, that's not your daily average loudness level?

116.9dB - no, that was a calibrated experiment, with one of Mario Martinez's (inactive member) files using the Krell amps and MartinLogans.

Is that from your speakers or your headphones?

Graphic Above? It's the JBL speakers.

It's a reasonable level for all day casual listening.

Another sample:

TV still running. No EQ, so some 100Hz room hump is evident. Content is the Smithsonian Channel, investigating if some Egyptian hieroglyphics explain the 10 plagues mention in the Bible (and commercials):

1536372451979.png
 

NorthSky

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You got some 9/11 history channel with the latest cancer dead people and the next to come in the future. Adjust the volume for a comfortable voice level, and then measure. • https://www.msn.com/en-ca/health/me...that-fateful-day/ar-BBMX459?OCID=ansmsnnews11

To reach 67dB how many watts is that? ...From your own system's volume knob (pot), which position on a clock would that be? ...Ten o'clock...roughly?

* Is your volume control analog or digital?
 
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RayDunzl

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To reach 67dB how many watts is that?

Guessing less than one dissipated at the speakers (each).

Using the MartinLogans (so I can measure speaker voltage), and seeing 0.7Vpk with a multimeter (with max hold), at 4 Ohms, that's 0.13 watts peak. (or some similar small amount).

From your own system's volume knob (pot), which position on a clock would that be?

On the preamp, it spins freely and is unmarked, but the display reads from 0 to 151.

At the moment, the preamp display is "30" (a unitless number, but something like .25 to .5dB per digit, never measured critically).

Is your volume control analog or digital?

Have both. Preamp has some kind of electronically selectable resistor set (analog), DAC and DSP recalculate the digits.
 
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NorthSky

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Cool, educational. That's why they say that the first watt is important. You want that watt, and below...0.1 watt, and just above, 3 watts or 5, clean.

I was just wondering if we can get a cleaner volume control in the analog or digital domain.

Ray, do you also listen with headphones sometimes?
 

trl

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Alright, how loud are we listening to, where on that dial are we turning up that volume control knob (potentiometer, volume attenuator)? How much break pedal (attenuation) are we releasing? What resistance is applied say when we are using normal power...less than 3 watts RMS? @ what average level are we listening to our music? What is the meter showing...0.3 watts? ...Little bit more...1.0 watts? It depends, passive or active listening...background music or front end serious music.
...From a normal stereo preamp, from a headphone amp.


@ low volume level listening we usually measure larger amount of THD.
And the more we crank the volume up the distortion level decreases, up to the power amp limit, where the distortion rises abruptly and clips.
With a quality amp the level of THD is low from 0.001 watts to say 5 watts.
Some amps have larger level of THD @ very low power...say less than 3 watts.

Using a quality amp, how much influence a volume pot can have on the sound output...measurable distortion level? Are there better potentiometers with less measured distortion, and if yes, what are the best ones and why are they measuring better?

The really potential issue might be with a DAC having built-in digital control is the noise level under really quiet environments and very sensitive speakers/headphones. The reason for this is the lack of gain attenuation between the input stage and output stage, basically the entire noise of the DAC's output + I/V stage + LPF stage + preamp stage + output stage is on your headphones/speakers. This noise only manifests with very sensitive IEM's for example or with very sensitive speakers (depending what you're going to amplify and drive). A regular potentiometer places between LPF stage and the preamp stage will lower both noise & volume and background noise will be virtually non-existent or outputs.

I've seen this behavior on Burson PLAY (ES9018K2M with built-in volume contro, 4V RMS/channel on DAC's outputs), but only with very sensitive 16 Ohms IEM's: placing a resistive divider or a regular 10 KOhms pot. "in the middle" reduced the background noise and the output volume, of course. Basically, "pot. in the middle" behavior is also why Objective2 has virtually nonexistent noise on outputs when driving sensitive IEM's.
 

Esotechnik

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What about statistical (ACF) delta-sigma conversion errors?
Many R2R DACs has "no missing codes" in description.
Audio Precision with D-S ADC and long averaging cannot detect ACF errors.
AP is old instrument initial for analog circuits, with some digital features.
sdm_fail.png
https://en.wikipedia.org/wiki/Analog_signal_processing#Linear_time-invariant_(LTI)

"Linearity and time-invariance are important because they are the only types of systems that can be easily solved using conventional analog signal processing methods. Once a system becomes non-linear or non-time-invariant, it becomes a non-linear differential equations problem, and there are very few of those that can actually be solved. (Haykin & Van Veen 2003)"

Delta-sigma DACs is not LTI system, has all missing codes and significant noise shaping.

ACF_random.png
 

amirm

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AP is old instrument initial for analog circuits, with some digital features.
Everything we want to analyze is analog. Don't care what happens upstream. We want to know what the analog signal is doing. The AP digitizes this analog signal and then processes it in software.

On the rest of your post, I am not clear what the issue is. DACs that we deal with are multibit so limit cycles are much less of a problem with them. Your references seem old and deal with 1-bit quantizers????
 

Esotechnik

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DACs that we deal with are multibit so limit cycles are much less of a problem with them
"Much less" is only words, not measurements.
IMHO we need true SAR ADC (no missing codes, without noise shaping) + Eye Diagram with meander signals, this is instrumental method vs. AK5394+FFT in AP.
https://www.diyaudio.com/forums/equ...rformance-audio-adc-project-ltc2380-24-a.html

My first (green) picture relating to fifth order sigma-delta modulator.

https://m.eet.com/media/1166738/295165-tmw_eye_freescale_fig4.jpg
 

amirm

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"Much less" is only words, not measurements.
IMHO we need true SAR ADC (no missing codes, without noise shaping) + Eye Diagram with meander signals, this is instrumental method vs. AK5394+FFT in AP.
https://www.diyaudio.com/forums/equ...rformance-audio-adc-project-ltc2380-24-a.html

My first (green) picture relating to fifth order sigma-delta modulator.
Like you said, that is only words, not measurements. You are not showing what the Audio Precision analyzer can do. So let's set the conditions similar to yours and compare:
APX Loopback with 1 million point FFT.png


Your graph on the left is using relative dB but unfortunately 0 dB is not set to signal level (what good is relative dB then???). Mine is set to 0 dB so compensating for that, the APx is much, much better. There is only one harmonic component at whopping -157 dB down from signal. In your case, you are getting -130 dB (again, referenced to 0 dB, not -6dB). You also have fair bit of noise and distortion components beyond that harmonic.

How does the APx55 get such superlative performance? It does so by using two ADCs. One handles the signal and then the other notches it out and measure what is left. The second ADC therefore is operating with no distortion since the signal is all gone. Through signal processing, the output of the two ADCs are then summed together. This is how you build a high-performance audio analyzer. Not just by brute force but rather, engineering smarts.

Noise floor is also lower in APx555 analyzer:
APX Loopback noise floor with 1 million point FFT.png


The above with the signal generator on but set to zero which disadvantages the APx555. Still, it beats your solution by 15 dB.

All of this is beside the point: the analyzer only needs to be better than devices we are testing. And the APx555 does that well, able to differentiate between the highest performance audio components we have tested with it.
 
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