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Topic: Disadvantages to linear phase low-pass filters? (Read 31967 times) previous topic - next topic
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Disadvantages to linear phase low-pass filters?

Reply #50 –
when you say "anti-imaging", don't you mean "anti-aliasing"?  This is confusing.
Be a false negative of yourself!

Disadvantages to linear phase low-pass filters?

Reply #51 –
Quote from: Nevod on
However, how comes that I get 18kHz ringing after filtering sharp transition from 150 hz signal to 550 hz one with a filter with 23.5 kHz cutoff? I understand that the transition shows itself as a HF spike in frequency domain, even despite it's at zero-crossing and both signal way below cutoff, but why do I get ringing below cutoff?


A pure tone has infinite duration. Any transition will "broaden" its spectrum, and if the spectrum extends to >23.5 kHz then of course the filter will do its work.


I don't know what your filter looks like, but if it is flat up to ~23.5 kHz and linear phase then it really should not ring at 18 kHz.

"I hear it when I see it."

Disadvantages to linear phase low-pass filters?

Reply #52 –
Quote from: Nystagmus on
when you say "anti-imaging", don't you mean "anti-aliasing"?  This is confusing.

Imagine upsampling (no interpolation) a 10 kHz sine sampled at 44.1 kHz by a factor 2. It will mirror to 34.1 kHz. That is imaging. (Since this happens in reconstruction the anti-imaging is also called reconstruction filter.)

Imagine sampling a 34.1 kHz sine at 44.1 kHz. It will alias to 10 kHz. That is aliasing.


But essentially it's just low pass filters.
"I hear it when I see it."

Disadvantages to linear phase low-pass filters?

Reply #53 –
Quote from: Nystagmus on
when you say "anti-imaging", don't you mean "anti-aliasing"? This is confusing.
Simply put: imaging happens in a DAC, aliasing happens in an ADC. Both require a low-pass filter to get rid of.

Disadvantages to linear phase low-pass filters?

Reply #54 –
Quote from: Arnold B. Krueger on
One approach would be to design the filter to have appreciable but still inaudible losses below 22.05 KHz.  But even that might not be necessary.

Aliasing happens at the time of sampling, so aliasing has already happened when you have those 44.1 kHz samples.



Quote from: Arnold B. Krueger on
In fact if you don't oversample, you don't need to worry about the anti-imaging since the images are not possible without oversampling or some other nonlinear processing.

Let's look at digital 101. The ADC has anti-imaging filters so that the 44.1 KHz digital data stream has no images. If you turn around and convert that data stream back into analog without further processing in the digital domain, where did the images come from?

Err, what?
Try the sampling theorem...
"I hear it when I see it."

Disadvantages to linear phase low-pass filters?

Reply #55 –
Quote from: xnor on
Quote from: Arnold B. Krueger on
One approach would be to design the filter to have appreciable but still inaudible losses below 22.05 KHz.  But even that might not be necessary.

Aliasing happens at the time of sampling, so aliasing has already happened when you have those 44.1 kHz samples.

Aliasing happens at the time of sampling,


True given that we assume that the source digitizer is incompetently designed, and the analog input signal  has significant content above the Nyquist frequency.  However, this is false in many cases.

For example, I'm digitizing a LP that was mastered from from a 44 KHz 48 KHz, or 50 kHz sampled digital master. There are a ton of these.  There is by definition no useful content above 22 or 25 KHz to be aliased unless the LP was incompetently made or badly damaged.

Another example is digitizing that is simply done competently as it generally is done. In a competent digitizer, the ADC is as a matter of course equipped with a filter with a sharp cutoff at or below Nyquist.

Even cheap audio interfaces and AVRs contain competently designed ADCs that do not alias.

Quote from: xnor on
Quote from: Arnold B. Krueger on
In fact if you don't oversample, you don't need to worry about the anti-imaging since the images are not possible without oversampling or some other nonlinear processing.

Let's look at digital 101. The ADC has anti-imaging filters so that the 44.1 KHz digital data stream has no images. If you turn around and convert that data stream back into analog without further processing in the digital domain, where did the images come from?


Err, what?
Try the sampling theorem...


Been there, done that. I suggest you do the same at your earliest convenience. ;-)

Disadvantages to linear phase low-pass filters?

Reply #56 –
Quote from: Arnold B. Krueger on
Quote from: saratoga on
You need to oversample in order to use a digital filter at all.


Oversampling may facilitate the process and improve the outcome, but it is not absolutely necessary.


I understand what you are saying, but your argument here presumes that oversampling is something like "running at an integer multiple of 44.1/48/96k", whereas the more correct engineering definition would be "running at any sampling rate in excess of the critical sampling rate".  So in your example of sampling a record at 48khz and then low passing a little below that, you would by definition be oversampled by whatever the bandwidth of your digital filter is. 

Disadvantages to linear phase low-pass filters?

Reply #57 –
Quote from: Arnold B. Krueger on
True given that we assume that the source digitizer is incompetently designed, and the analog input signal  has significant content above the Nyquist frequency.  However, this is false in many cases.

For example, I'm digitizing a LP that was mastered from from a 44 KHz 48 KHz, or 50 kHz sampled digital master. There are a ton of these.  There is by definition no useful content above 22 or 25 KHz to be aliased unless the LP was incompetently made or badly damaged.

Another example is digitizing that is simply done competently as it generally is done. In a competent digitizer, the ADC is as a matter of course equipped with a filter with a sharp cutoff at or below Nyquist.

Even cheap audio interfaces and AVRs contain competently designed ADCs that do not alias.


Sure, but that is irrelevant to what WernerO asked.


Quote from: Arnold B. Krueger on
Been there, done that. I suggest you do the same at your earliest convenience. ;-)

I'm sorry but if you ask "where did the images come from", which you did, then you are clueless about sampling. So whatever you did, it was not understanding sampling.

So go ahead and answer your own question. I'm highly curious about your answer.
"I hear it when I see it."

Disadvantages to linear phase low-pass filters?

Reply #58 –
Quote from: xnor on
Quote from: Arnold B. Krueger on
True given that we assume that the source digitizer is incompetently designed, and the analog input signal  has significant content above the Nyquist frequency.  However, this is false in many cases.

For example, I'm digitizing a LP that was mastered from from a 44 KHz 48 KHz, or 50 kHz sampled digital master. There are a ton of these.  There is by definition no useful content above 22 or 25 KHz to be aliased unless the LP was incompetently made or badly damaged.

Another example is digitizing that is simply done competently as it generally is done. In a competent digitizer, the ADC is as a matter of course equipped with a filter with a sharp cutoff at or below Nyquist.

Even cheap audio interfaces and AVRs contain competently designed ADCs that do not alias.


Sure, but that is irrelevant to what WernerO asked.


I guess Xnor you can't read well enough to know that I am not answering Werner o's question in this post. A person with normal intelligence and familiarity with reading threads might notice that his name appears nowhere in my answer.

I was answering your poorly informed claim:  "Aliasing happens at the time of sampling, so aliasing has already happened when you have those 44.1 kHz samples."

In fact, in general there is no aliasing in most 44.1 KHz data streams for a variety of good and well-known reasons.

To reiterate what has apparently already flown over your head once Xnor, aliasing does not have to happen at the time of sampling. It takes circumstances that are not always present, for it to happen to an audible degree.  In fact those circumstances might be pretty rare in general. 

I can understand how a person who lacks significant practical familiarity with how modern digital works in the real world might think otherwise.



Disadvantages to linear phase low-pass filters?

Reply #59 –
"I hear it when I see it."

Disadvantages to linear phase low-pass filters?

Reply #60 –
Quote from: saratoga on
Quote from: Arnold B. Krueger on
Quote from: saratoga on
You need to oversample in order to use a digital filter at all.


Oversampling may facilitate the process and improve the outcome, but it is not absolutely necessary.


I understand what you are saying, but your argument here presumes that oversampling is something like "running at an integer multiple of 44.1/48/96k", whereas the more correct engineering definition would be "running at any sampling rate in excess of the critical sampling rate".  So in your example of sampling a record at 48khz and then low passing a little below that, you would by definition be oversampled by whatever the bandwidth of your digital filter is.


Completely wrong headed, as exemplified by the fact that I clearly said "I'm digitizing a LP that was mastered from from a 44 KHz 48 KHz, or 50 kHz sampled digital master."

What I did not say clearly was the sample rate of my new recording. Let's say it was 96 KHz or 176 KHz  or even some other odd frequency >> 50 KHz...

You assumed... wrongly.

Disadvantages to linear phase low-pass filters?

Reply #61 –
Quote from: Arnold B. Krueger on
Quote from: saratoga on
Quote from: Arnold B. Krueger on
Quote from: saratoga on
You need to oversample in order to use a digital filter at all.


Oversampling may facilitate the process and improve the outcome, but it is not absolutely necessary.


I understand what you are saying, but your argument here presumes that oversampling is something like "running at an integer multiple of 44.1/48/96k", whereas the more correct engineering definition would be "running at any sampling rate in excess of the critical sampling rate".  So in your example of sampling a record at 48khz and then low passing a little below that, you would by definition be oversampled by whatever the bandwidth of your digital filter is.


Completely wrong headed, as exemplified by the fact that I clearly said "I'm digitizing a LP that was mastered from from a 44 KHz 48 KHz, or 50 kHz sampled digital master."

What I did not say clearly was the sample rate of my new recording. Let's say it was 96 KHz or 176 KHz  or even some other odd frequency >> 50 KHz...

You assumed... wrongly.


I fail to see what your point is.  Aside from disagreeing with my example, what does this have to do with anything?

Disadvantages to linear phase low-pass filters?

Reply #62 –
Nothing, he just brings up examples that evade the issues and questions, and then later claims you are wrong for not reacting to his constructed examples before he even posted them... in other words, you're not a freaking clairvoyant.
"I hear it when I see it."

Disadvantages to linear phase low-pass filters?

Reply #63 –
Quote from: Arnold B. Krueger on
I can understand how a person who lacks significant practical familiarity with how modern digital works in the real world might think otherwise.

Dunning-Krueger

Would you please answer your question "where did the images come from" instead of evading?


Oh, I found something:
Quote from: Arnold B. Krueger on
The Philips DACs that introduced oversampling justified their use of oversampling with its dynamic range/SNR benefits. not any improvements in bandpass. 

In fact if you don't oversample, you don't need to worry about the anti-imaging since the images are not possible without oversampling or some other nonlinear processing.

(emphasis by me)
Are you serious? 
This demonstrates a complete lack of understanding for sampling and reconstruction.

But please elaborate on this.
"I hear it when I see it."

Disadvantages to linear phase low-pass filters?

Reply #64 –
Quote from: xnor on
Quote from: Arnold B. Krueger on
In fact if you don't oversample, you don't need to worry about the anti-imaging since the images are not possible without oversampling or some other nonlinear processing.

This speaks volumes.

Disadvantages to linear phase low-pass filters?

Reply #65 –
Even if you don't oversample, you still need a low-pass filter cutting out anything above Nyquist (Safari wants to correct this to Nyqvist, I guess Swedish actors can afford to get their names into spelling checkers, while science goes overlooked.) or else you get, well, imaging.

Disadvantages to linear phase low-pass filters?

Reply #66 –
Arny does not seem to want to come back.
Anyway, I will still post so that others can understand.


Two signals in the time domain:


Now in the frequency domain (analog signal - continuous spectrum):


Frequency domain (sampled signal - discrete spectrum):

(x-axis in sampling rates, so 0.5 would be Nyquist)


That is why you need a reconstruction filter, that suppresses images >0.5.
And this also explains aliasing. If the spectrum was broader, or the sampling rate lower, then these spectra would overlap.
"I hear it when I see it."

Disadvantages to linear phase low-pass filters?

Reply #67 –
Quote from: saratoga on
I fail to see what your point is.  Aside from disagreeing with my example, what does this have to do with anything?


I feel like I'm dealing with Golden Ears who think that everything matters, all of the time.  No concept of or understanding of quantification.

If there is -100 dB of it, then they panic, thinkng it is going to fry their precious high end amplifiers and tweeters;.

None of them have apparently ever done any ABX testing relating to the audibility of aliasing, imaging or the modulation effects.

Disadvantages to linear phase low-pass filters?

Reply #68 –
I don't see anyone panicking but you, Arny.

Where did anyone in this thread say anything about audibility of -100 dB aliasing? And saratoga didn't even make a point about audibility...
"I hear it when I see it."

Disadvantages to linear phase low-pass filters?

Reply #69 –
Quote from: Arnold B. Krueger on
True given that we assume that the source digitizer is incompetently designed,


The only incompetence in this thread is yours.

This thread is not the first one that shows up your ignorance with respect to sampling.

What is staggering is that you refuse to learn.

Disadvantages to linear phase low-pass filters?

Reply #70 –
Quote from: xnor on
I don't see anyone panicking but you, Arny.


Me worry? ;-)

I may be the only person posting on this thread who has heard a 44/16 system that lacks low pass filtering.

Have you?

Typical debating trade tactic - turn the argument around.  Two can play!

Quote
Where did anyone in this thread say anything about audibility of -100 dB aliasing? And saratoga didn't even make a point about audibility...


I just threw that number out to get a response, a tactic that obviously worked.

So if its not -100 dB, give us a number for how much low pass filtering is required, if you know one... ;-)

Disadvantages to linear phase low-pass filters?

Reply #71 –
After all this time, we really have to go back and discuss the sampling theorem? It's sad to see how carefully demonstrated and build up reputation can be so utterly be destroyed by just a few silly statements.

Arny, I hereby warn you to watch your tone (ToS #2), and stop ad-hominem and argument-from-authority bullshit, and stop derailing this and other topics (ToS #5).
It's only audiophile if it's inconvenient.

Disadvantages to linear phase low-pass filters?

Reply #72 –
Quote from: Kohlrabi on
After all this time, we really have to go back and discuss the sampling theorem? It's sad to see how carefully demonstrated and build up reputation can be so utterly be destroyed by just a few silly statements.


You might want to point out where there were actual problems of that kind.

Disadvantages to linear phase low-pass filters?

Reply #73 –
Quote from: Arnold B. Krueger on
I may be the only person posting on this thread who has heard a 44/16 system that lacks low pass filtering.

Have you?

That, of course, completely negates all the nonsense you've produced above ... NOT. And it is again completely irrelevant.

I actually have "heard" aliasing and imaging with different kind of filters and even without, but according to you, there are no images because they are impossible, right?
That's because you don't understand sampling.


Quote from: Arnold B. Krueger on
Quote
Where did anyone in this thread say anything about audibility of -100 dB aliasing? And saratoga didn't even make a point about audibility...


I just threw that number out to get a response, a tactic that obviously worked.

So if its not -100 dB, give us a number for how much low pass filtering is required, if you know one... ;-)

It seems I have to repeat things for you several times until you get them: saratoga didn't even make a point about audibility.

There is no single number you can put on that anyway. I will not engage further in your red herrings.
"I hear it when I see it."

Disadvantages to linear phase low-pass filters?

Reply #74 –
Quote from: xnor on
There is no single number you can put on that anyway.


Of course there is a whole raft of single numbers that can put on the ear's tolerance for digital artifacts. Let's start with -140 dB and work upwards...

But more seriously, we can use the applicable Fletcher Munson curve.

Finally, it would seem like the well known masking curves would apply. 

Not single numbers but limiting the answers to single numbers is not a goal post that I moved.

Is it?