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General debate thread about audio measurements

March Audio

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Re the comments about ESS filters allegedly being under damped, well here is a dirac pulse played back from Adobe Audition and measured from the output of my ESS based DAC. Note the period (frequency) of the ringing. Spot the difference. The output looks as you would expect. Nothing unusual going on here at all.

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mansr

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Re the comments about ESS filters allegedly being under damped
Regarding that, it's not even the correct terminology. Talk of damping only makes sense when there is a resonance involved. As there is none here (a FIR filter cannot exhibit resonance), the term is being misapplied. For the same reason, referring to the sinc response as "ringing" is also incorrect.
 

March Audio

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Regarding that, it's not even the correct terminology. Talk of damping only makes sense when there is a resonance involved. As there is none here (a FIR filter cannot exhibit resonance), the term is being misapplied. For the same reason, referring to the sinc response as "ringing" is also incorrect.
Indeed.
 

Blumlein 88

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Re. CD motor control.

There might be a better way of putting the last bit of my previous post:

The motor isn't regulated against a crystal-controlled reference frequency; it is regulated against a crystal-controlled reference count.

The former allows for cumulative blips, errors and offsets over time, and the myth (I claim it is anyway) is that the subsequent electronics smooths out the speed variations.

The latter doesn't allow for any such errors over time *and* makes the system immune to transport quality. It uses almost the same basic hardware, but with a slight re-arrangement achieves a fundamentally better result - which is what elegant engineering is all about :).

Yes, and that Pioneer player, which was actually a universal player that could do SACD and whatever the other one besides CD (DVD-Audio?) is the only case I've seen. It did cause JA in an article to place it among the worst jitter examples he had measured. If I recall he uses a 30 second file for that or maybe it was 60 seconds. Have a copy of his file somewhere. The first 15 seconds being horrible gave a pretty poor overall result when it averaged in for the jtest track. Yet after those first 15 seconds that player was actually pretty clean on the Jtest.
 

Calexico

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@amirm @Blumlein 88
Hello i report my question here to not disturb other threads .
Why not measuring the quality of the digital + analog filter of the dacs to see how the ultrasonic noise is handled?
A test that show the thd+ noise up to very high frequencies to see if they are filtered properly.
I'm curious if filters behave the same with different samplerates.
I'm sure the digital filter is adapted to fs/2.
So with bigger samplerate the cut off freq in not the same. Maybe there is ultrasonic more noise from the digital to analog conversion for > 20khz freq.
I think ultrasonic noise although not in hearable range can make emi and can interract with components that's why i ask for a test to show it.

That could explain why we can detect differences between opamp that react differently with those ultrasonics noise.
 
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Calexico

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This is another total red herring. Any potential ultrasonic filter ringing is at very low level. You have to remember that music content in the transition band might be -70 dB down. Its low pass anti alias filtered. There is very little content to make a reconstruction filter ring at nyquist. Any ringing is therefore much further down in level and above your hearing range.
Ringing not hearable could interract with components.
It's always better to have no ultrasonic at all or at very low level.
That's why smps power supply are not good if not properly filtered. If ultrasonic noise from the switching frequency isn't properly filtered it interact with components that doesn't perform optimally.

Why ringing isn't filtered? If it's not in hearable range it could be filtered no?

All datasheet of dacs recommend low pass filter on output. That means that it's important to eliminate all noise even if it's not in hearable range.
 
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Calexico

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Lol you filter the ringing with a filter that produce ringing :)
I think it's impossible to get rid of ringing.
 

amirm

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Why not measuring the quality of the digital + analog filter of the dacs to see how the ultrasonic noise is handled?
I run them when there is a reason to run them:

index.php
 
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777

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-80dB at the output dac will be approx -50dB at the speakers(to 2.5Vrms). That mean approx. 15mVpp at 28khz.
 

trl

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See

What is the reason? How do you know?
Same test with a 30khz tone won't have more ultrasonics?

You only run these tests when there's a concern there might be too much ultrasonics on the outputs that might cause overheating the output stage on the amplifiers or to check for bad behavior of DACs or their internal low-pass filters.

Otherwise, human don't hear ultrasonics so shouldn't affect us as much as the mosquitos.
 

Calexico

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You only run these tests when there's a concern there might be too much ultrasonics on the outputs that might cause overheating the output stage on the amplifiers or to check for bad behavior of DACs or their internal low-pass filters.

Otherwise, human don't hear ultrasonics so shouldn't affect us as much as the mosquitos.
I said ultrasonic can interract with other components and they don't work properly. It's usefull to have an idea of the ultrasonic noise
 

Xulonn

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I said ultrasonic can interract with other components and they don't work properly. It's useful to have an idea of the ultrasonic noise

Useful to whom and for what reason? Useful to your dog and his hearing acuity that can reach up to 45kHz?

For us mere mortal humans, if it doesn't affect music playback in the audible range - and no audible sonic effects can be detected via measurement or blind testing/listening, why should anyone be concerned about it? (Other than being curious about an outlying and probably irrelevant aspect of consumer audio.)
 

amirm

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What is the reason? How do you know?
Usually to debunk with data what people assume is there, but is not.

As to "how I know," try asking your doctor that question. Be careful as he throws you out of his office! :D
 

Calexico

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Ok so you say analog low pass filter are senseless.
Every datasheet show analog lpf on the output to filter ultrasonic content.
Every dac has analog low pass filter.
Then you sould tell all manufacturer that it's stupid to filter ultrasonic content.
If it's there is for something.
If it's there we sould evaluate their performance.

I said it can interact with digital amps in the modulation also maybe in emi.

I'm not a pro i don't know exemples why ultrasonic is badb butif every pdf of dac chips show an analog lpf to filter ultrasonic noise it means it's important.
 

amirm

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I'm not a pro i don't know exemples why ultrasonic is badb butif every pdf of dac chips show an analog lpf to filter ultrasonic noise it means it's important.
Lack of proper reconstruction filter in a DAC causes aliasing in the audible band. That is why it is there.

Listen to audio samples in the Wiki on aliasing: https://en.wikipedia.org/wiki/Aliasing

Please don't keep saying this and that is bad unless you can demonstrate it. That is our rule in this forum. Don't repeat myths created by non-technical people elsewhere as something factual, then demand this and that measurement. It is not our job to build on false premises.
 

Calexico

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@amirm

Exctract from the ak4490 datasheet:
''The internal switched-capacitor filters attenuate the noise generated by the delta-sigma modulator beyond the audio passband. Figure 40 shows an example of external LPF circuit summing the differential outputs by an op-amp.
Figure 41 shows an example of differential outputs and LPF circuit example by three op-amps.''

So there is low pass filter in the dac chip and also in analog output stage.

There are there to get rid of ultrasonic noise generated from the delta sigma modulator.

When why not evaluating it ?

If designer of the dac chip say ultrasonic from the delta sigma modulator must be filtered then i trust it.

I'd like to see if there are differences there between dac and between output stages.
 

Calexico

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@amirm then from same akm datasheet
''It is recommended for SACD format book (Scarlet Book) that the filter response at SACD playback is an analog Low pass filter with a cut-off frequency of maximum 50kHz and a slope of minimum 30dB/Oct. The AK4490 can achieve this filter response by combination of the internal filter (Table 32) and an external filter (Figure 42).''

No test show if the lpf of a dac is optimised for cd or sacd or high res.
 

amirm

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@amirm

Exctract from the ak4490 datasheet:
''The internal switched-capacitor filters attenuate the noise generated by the delta-sigma modulator beyond the audio passband. Figure 40 shows an example of external LPF circuit summing the differential outputs by an op-amp.
Figure 41 shows an example of differential outputs and LPF circuit example by three op-amps.''

So there is low pass filter in the dac chip and also in analog output stage.

There are there to get rid of ultrasonic noise generated from the delta sigma modulator.

When why not evaluating it ?
The problem is that you write more than you read. Did not not see this graph in the Topping D50s where you started this argument?

index.php


Even if I had not post the above measurements, audibility of these filters is highly questionable.
 
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