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Mastering Captured Vinyl For CD
bandpass
post Dec 13 2008, 19:43
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QUOTE (2Bdecided @ Dec 13 2008, 18:17) *
How did you generate these? (Not that I doubt - just interested).


Well, it might sound like doing it the hard way, but it was something I wanted to do anyway: I extricated the filter generator from the resampler in the latest SoX source code and ran it on its own.

An interesting question is at what phase response is the ringing least audible---for me it seems to be around 030.

-bandpass
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2Bdecided
post Dec 14 2008, 15:33
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Certainly stacking them up in fb2k and playing through them, the click seems most click-like with least ringing around file 030. What do the numbers correspond to?

If you look at the waveform, 030 has less post-ring than 000, but no pre-ring. In fact it's the shortest filter with no pre-ring at all, which probably explains the preference.

I always "thought" minimum phase was the shortest filter, so maybe I don't understand.

Cheers,
David.
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bandpass
post Dec 14 2008, 16:39
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QUOTE (2Bdecided @ Dec 14 2008, 14:33) *
Certainly stacking them up in fb2k and playing through them, the click seems most click-like with least ringing around file 030. What do the numbers correspond to?


The numbers are percentage phase response; so 000 is minimum phase and 100 is maximun phase. You'll need to use a dB amplitude scale with the impulse to see what's going on---linear amplitude scale won't cut it.
E.g. 030 does have pre-ring, but you won't see it with linear amplitude.

-bandpass
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KikeG
post Dec 14 2008, 19:27
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I think there are 2 different claims to prove about this ringing issue.

(1) Whether brickwall filtering causes ringing or not.
(2) If there is ringing, whether this ringing is audible or not.

As for (1), let's restrict just to linear phase filters for simplicity. Linear phase filters are filters that have no phase distortion, or in other words, filters that don't modify phase is at all (but for a simple constant time delay to the signal). A linear phase brickwall filter is no other thing than the sinc function. As you can see, the fourier transform, or in other words, the frequency domain view of this function is the rectangular function, this is, a function where there the result is 1 up to a frequency and is 0 from this frequency to infinite, or the maximum sampled frequency of this system. This is obviously the same than a brickwall filter.

As you can see, the time-domain view of this funcion has what is commonly called pre and post ringing, a fading-in and fading-out sinusoid of the same frequency than the filter cutoff.

All this can be simulated and verified in CEP or Adobe Audition creating an impulse signal, brickwall filtering it with a FFT filter, and looking al the resultant signal. In frequency domain you can see the ringing using the spectral view, or using a short FFT analysis (128 point for example) in the temporal proximities of the filtered impulse.

So, from my point of view, point (1) is proved.

Now let's go for (2), is it audible? Well, the question for me is if there is something that prevents it from being audible. The answer is that there are two things that can prevent it:

The first one is the frequency of the ringing. If it is outside of the audible range, then it is inaudible. So brickwall filters over 20 KHz will not be audible, which is the case of cd-audio antialiasing and reconstruction filters.

The second thing is the length of the ringing. Due to a propery of out ear called temporal masking, a faint signal may get masked by another louder signal very close in time, this is what is called temporal masking. Faint signals before a loud signal need to be very close to this loud signal to get masked, in other words, our ear is not very prone to backwards temporal masking. But faint signals after the loud signal may be more away from the loud signal and still get masked, in other words, our ear is more prone to forward temporal masking.

So, if the ringing due to the brickwall filtering is at an audible frequency but is very short in time, it will be very probably masked due to this temporal masking property of our hearing. If the ringing is not very short but not very long, the pre-ringing will be audible but the post-ringing not. And if it is very long, both pre and post ringing may get audible.

What does the lenght of the ringing depends on? Just on the length of the filter, in other words, the number of samples used to compute it, which is the same as the order of the filter. A 65K-samples filter will have 32K samples of pre-ringing and 32K samples of post ringing. A long filter is sharper in frequency domain, but has longer ringing. A short filter is less sharp in frequency domain, but has shorter ringing. A long "softened" brickwall filter will have shorter ringing too.

So, is it audible? Depends on the cutoff of the brickwwall, the lenght of the filter and the sampling frequency. At 44.1 KHz and a brickwall cutting at an audible frequency, A 16K filter has 0.2 s of pre-ringing, which is easily audible over an impulse. A 512 samples filter has 6 ms of pre-ringing, which is much less audible, but probably still audible. A 128 samples filter is less than 2 ms, I think it is not audible. A 256 maybe yes, maybe not.

I think the difference between the 16K and the 512-samples filter is very audible. See the attached file with examples of the results of these filters at a 4KHz cutoff over an impulse signal. I had no time to ABX, but the difference is obvious. The files are time-aligned and level matched at 0.01 dB or less, so no processing is needed. Both the level match of signals in the baseband and frequency response of filters can be checked doing a dual-channel FFT of the stereo file. So (2) is proved too.

Finally, note that if the signal to be filtered has no content at the cutoff frequency, there will be no ringing to talk of. And if the signal is not impulsive, the ringing will be nearly nonexistent compared with the non-impulsive signal.

Sorry for any typos, at the end I was on a hurry when writing this.

This post has been edited by KikeG: Dec 14 2008, 23:52
Attached File(s)
Attached File  4Kbrickwall.zip ( 119.5K ) Number of downloads: 204
 
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2Bdecided
post Dec 14 2008, 22:05
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I agree with all of that. Especially the "why wouldn't it be audible" approach - I've already referenced the temporal masking data on this.

But you've dragged us back to the "harder" question of the audibility of ringing in two filters with non-identical frequency response - i.e. both linear phase, one "gentle". I have no problem with this, but this is where I started two pages ago, and was criticised, so I'd retreated to the even "safer" position of the audibility of ringing in two filters with identical frequency response.

Still, in either case, I can't believe anyone can plausibly claim the ringing from a brick wall filter is not audible when the transition band is within the audible range, and there's content within the original signal to exercise the ringing. I hope Arny will be gracious enough to retract his former claim and accept that this is the case.

Cheers,
David.

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KikeG
post Dec 14 2008, 23:44
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Yes, I restricted to linear phase in order to focus in the two different claims over this ringing issue, and the importance of the filter length over the audibility. It's hard to believe the audible differences between the long and short filter are not due to ringing, because the audible difference is that one file rings and the other does not (or not as much). Also, your files were properly level matched in the pass band, Arny's normalization over the whole band probably destroyed this level matching.

As you say, going the case of exact same frequency response and just changing phase of the filter (and associated location of ringing) makes even more evident that the audible differences are due to these different locations of ringing, so the conclusion is that this ringing is audible.
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Arnold B. Kruege...
post Dec 15 2008, 14:59
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QUOTE (2Bdecided @ Dec 14 2008, 16:05) *
Still, in either case, I can't believe anyone can plausibly claim the ringing from a brick wall filter is not audible when the transition band is within the audible range, and there's content within the original signal to exercise the ringing. I hope Arny will be gracious enough to retract his former claim and accept that this is the case.


I'm very impressed and convinced by the data. There's no question about the level matching or frequency response matching. The samples are totally matched in the pass band, vary only enough to convince me that they are really different in the transition band, and differ measurably but inconsequentially in the rejection band. Of course the temporal data is definitive and obvious.

Listening test data for at least the 2 extreme cases is equally clear and definative. ABXing to any reasonble level of statistical difference is trivially easy (even using my ancient ears diminished by a bad head cold).

Furthermore, the 5% and 100% samples clearly and unmistakably sound like they are whistling. The 100% sample seems to be whistling around 4 KHz and the 5% sample a little less, a little lower. The linear phase filter seems to minimze this effect.

In terms of temporal dispersal, the linear phase filter seems to have reduced temporal dispersal, even as compared to the original wave.

Since the 50% is well-qualified as a brick wall filter, there is no obvious proof that brick wall filters are necessarily evil.

One of the less obvious characteristics of filter is the degree to which it causes the data to have increased peak amplitude in either direction. Again, the linear phase filter seems to be the winner.

I hear and see a lot of justification for linear phase filtering.
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krabapple
post Dec 15 2008, 17:59
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QUOTE (KikeG @ Dec 14 2008, 13:27) *
Now let's go for (2), is it audible? Well, the question for me is if there is something that prevents it from being audible. The answer is that there are two things that can prevent it:

The first one is the frequency of the ringing. If it is outside of the audible range, then it is inaudible. So brickwall filters over 20 KHz will not be audible, which is the case of cd-audio antialiasing and reconstruction filters.



I just thought this should be emphasized.
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2Bdecided
post Dec 15 2008, 18:36
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QUOTE (Arnold B. Krueger @ Dec 15 2008, 14:59) *
In terms of temporal dispersal, the linear phase filter seems to have reduced temporal dispersal, even as compared to the original wave.

Since the 50% is well-qualified as a brick wall filter, there is no obvious proof that brick wall filters are necessarily evil.
So you don't hear any chirping with the linear phase filter?

And you think the 4kHz brick wall linear phase filtered click has "reduced temporal dispersal, even as compared to the original wave"?

Cheers,
David.
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bandpass
post Dec 15 2008, 18:46
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QUOTE (bandpass @ Dec 14 2008, 15:39) *
The numbers are percentage phase response; so 000 is minimum phase and 100 is maximun phase. You'll need to use a dB amplitude scale with the impulse to see what's going on---linear amplitude scale won't cut it.

Here's a graph (time x-axis, amplitude dB y-axis) of the phases 0-50% (minimum to linear phase). Phases 55-100% are not shown but look like phases 45-0% mirrored about the y-axis.

Due to differences between forward and backward temporal masking, linear phase should not sound the best to most people. (But I agree that this does not apply to filters @ >20kHz).

-bandpass



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2Bdecided
post Dec 15 2008, 21:42
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QUOTE (bandpass @ Dec 14 2008, 16:39) *
You'll need to use a dB amplitude scale with the impulse to see what's going on---linear amplitude scale won't cut it.
Missed that first time around - thanks for re-stating it!

IIRC there's a comment by Brian Moore that temporal pre-masking decreases greatly with training, making the pre/post difference even more stark. Something like 3ms vs 20ms for a masker/maskee combination, but that's from memory - I've lost the paper.

Cheers,
David.
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Arnold B. Kruege...
post Dec 16 2008, 11:14
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QUOTE (2Bdecided @ Dec 15 2008, 12:36) *
QUOTE (Arnold B. Krueger @ Dec 15 2008, 14:59) *
In terms of temporal dispersal, the linear phase filter seems to have reduced temporal dispersal, even as compared to the original wave.

Since the 50% is well-qualified as a brick wall filter, there is no obvious proof that brick wall filters are necessarily evil.
So you don't hear any chirping with the linear phase filter?


Vastly less, as compared to the 5% and 100% samples. Comparison with the original wave is invalid because it has a vastly different frequency response.

QUOTE
And you think the 4kHz brick wall linear phase filtered click has "reduced temporal dispersal, even as compared to the original wave"?


Again, comparison with the original wave is obviously invalid, as it has vastly different frequency response.

I think we may need to review the purpose of the exercise. We are trying to filter out HF noise as effectively as possible with minimal effect on SQ.

Observing that no filter affects sound less than a potentially effective filter doesn't seem to help very much.
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2Bdecided
post Dec 16 2008, 12:20
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QUOTE (Arnold B. Krueger @ Dec 16 2008, 11:14) *
QUOTE (2Bdecided @ Dec 15 2008, 12:36) *
So you don't hear any chirping with the linear phase filter?
Vastly less, as compared to the 5% and 100% samples.
OK, that's fine, no one can argue with that.

QUOTE
I think we may need to review the purpose of the exercise. We are trying to filter out HF noise as effectively as possible with minimal effect on SQ.
We were, but we've moved on a long way from the original question. We're in the audible range now, for one thing.


So let me turn this around.

My hypothesis is that a brick wall filter rings, and that this ringing can be audible and objectionable. A more gentle filter will ring substantially less, to the point where the ringing is substantially inaudible.

The spectral and temporal responses of the gentle filter are different from those of the brick wall filter, but whereas the change in spectral response is small and rarely of any practical importance (I don't say whether it's audible or not), the change in temporal response is dramatic, clearly audible, and solves an objectionable problem with brick wall filtering.

How would you prove / disprove this in a way that you would find convincing?

Suitable samples are at the end of KikeG's post:
http://www.hydrogenaudio.org/forums/index....st&p=604669

Cheers,
David.

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Arnold B. Kruege...
post Dec 16 2008, 15:03
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[quote name='2Bdecided' date='Dec 16 2008, 06:20' post='604891']
[quote name='Arnold B. Krueger' post='604877' date='Dec 16 2008, 11:14']
[quote name='2Bdecided' post='604792' date='Dec 15 2008, 12:36']So you don't hear any chirping with the linear phase filter?[/quote]

Vastly less, as compared to the 5% and 100% samples.[/quote]

OK, that's fine, no one can argue with that.
[/quote]

I think we may need to review the purpose of the exercise. We are trying to filter out HF noise as effectively as possible with minimal effect on SQ.[/quote]

We were, but we've moved on a long way from the original question. We're in the audible range now, for one thing.[/quote]

We always were in the audible range, when we're talking effective filters in the middle of the frequency range of most sensitive human hearing.

OTOH, we always have to keep our eyes on our masking curves.

The impulse is composed of every frequency that isn't being filtered out, so conceivably it is masking concurrent sounds in the same frequency range around the time it has peak amplitude. That potentially includes the ringing.

The impulse is also a very loud sound at the time its amplitude peaks, so it is masking sounds that are happening at about the same time. That potentially includes the ringing.

I suspect that if we can appropriately control the duration, amplitude and shape of the envelope of the ringing, we might mask it all.

[quote]
My hypothesis is that a brick wall filter rings, and that this ringing can be audible and objectionable.
[/quote]

You do understand that the filter need not be brick wall in order to ring. As a matter of fact, our test signal rings pretty vigorously with no filtering at all. Also, I applied a 20 Hz impulse to a 4th order filter, and it rang as well. Just less, and more clearly under a presumed temporal masking curve.

[quote]
A more gentle filter will ring substantially less, to the point where the ringing is substantially inaudible.
[/quote]

But, more noise gets through.

[quote]
The spectral and temporal responses of the gentle filter are different from those of the brick wall filter,
[/quote]

Major side effect - remove less noise for a given effect on the music.

[quote]
but whereas the change in spectral response is small and rarely of any practical importance (I don't say whether it's audible or not),
[/quote]

I believe that it was audible for a more gentle filter that was proposed earlier in the thread.

[quote]
the change in temporal response is dramatic, clearly audible, and solves an objectionable problem with brick wall filtering.
[/quote]

But of course, less filternig, less noticable.

[quote]
How would you prove / disprove this in a way that you would find convincing?
[/quote]

First I think we need to agree on what we are expecting the filter to do in terms of its first order effect.

The ringing, etc., is a second order or higher effect.

[quote]
Suitable samples are at the end of KikeG's post:
http://www.hydrogenaudio.org/forums/index....st&p=604669
[/quote]

Suitable for what?

Those samples only focus on the secondary effects, and show nothing about any balance between primary and secondary effects.

As long as low slope, no slope filtering has no cost associated with it, it will always be the means of choice. After all, the best way to do nothing is to simply do nothing. ;-)

BTW this post is a mess of quotes, but I've stopped trying to please this conference software. I can balance quotes on other HTML forums, no sweat. There seem to be some hidden agendas.

At least on Usenet, we've got tools that handle quoting automagically.
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2Bdecided
post Dec 16 2008, 16:31
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QUOTE (Arnold B. Krueger @ Dec 16 2008, 15:03) *
BTW this post is a mess of quotes, but I've stopped trying to please this conference software. I can balance quotes on other HTML forums, no sweat. There seem to be some hidden agendas.
At the top of your post, you opened three quotes, then closed five. At least that is what is shown.

Cheers,
David.
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2Bdecided
post Dec 16 2008, 16:53
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QUOTE (Arnold B. Krueger @ Dec 16 2008, 15:03) *
I suspect that if we can appropriately control the duration, amplitude and shape of the envelope of the ringing, we might mask it all.
But when constrained to a linear phase brick wall filter, we have no independent control of any of those things - they are all pre-defined. A linear phase brick wall filter is a sinc function. That is what it is. The only variables are the cut off frequency, and where you decide to truncate the time-domain waveform (since an ideal sinc function is infinite).

KikeG has already covered making it "less brick wall" by truncating/windowing the response. This is the entire point - doing this makes the filter more gentle in its frequency response and (obviously) shorter in its temporal response.

QUOTE
You do understand that the filter need not be brick wall in order to ring.
The vast majority of filters ring. What's that got to do with the price of fish? The problem is whether the ringing is audible, and can be reduced so that it is not. Linear phase brick wall filters create audible ringing unless you make them less brick wall like!

QUOTE
QUOTE
A more gentle filter will ring substantially less, to the point where the ringing is substantially inaudible.
But, more noise gets through.
Ah, so we come to the question of what the filter is supposed to be doing, and whether a sharp cut off is more important than the avoidance of ringing.

That depends on the application. The point is whether the brick wall filter introduces audible ringing. You stated that it did not. So while you suggest I'm assigning a "zero cost" to the gentle cut off, you are assigning a "zero cost" to the ringing.

In truth, both have a cost - judging which is preferable is a matter for the designer, and application specific.

However, that's was not your original point at all: you implied that ringing is a "zero cost" problem because you believe there is no ringing, and if there is, it isn't audible.


I'm not asking you how you would prove to your satisfaction "what is the best filter for this job" or even "what is this job" - I'm asking how would you prove or disprove that the ringing from brick wall filters is audible.

Cheers,
David.
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krabapple
post Dec 16 2008, 18:28
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QUOTE (2Bdecided @ Dec 16 2008, 10:31) *
QUOTE (Arnold B. Krueger @ Dec 16 2008, 15:03) *
BTW this post is a mess of quotes, but I've stopped trying to please this conference software. I can balance quotes on other HTML forums, no sweat. There seem to be some hidden agendas.
At the top of your post, you opened three quotes, then closed five. At least that is what is shown.

Cheers,
David.



Not just that, there appears to be a ten-quote limit (brickwall filter? laugh.gif ) per post --I've run into it before, with complex replies.

It's not an 'agenda', Arny, though it might indicate that post could use trimming.

This post has been edited by krabapple: Dec 16 2008, 18:42
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Kees de Visser
post Dec 16 2008, 18:34
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QUOTE (bandpass @ Dec 15 2008, 18:46) *
Here's a graph (time x-axis, amplitude dB y-axis) of the phases 0-50% (minimum to linear phase). Phases 55-100% are not shown but look like phases 45-0% mirrored about the y-axis.
The iZotope RX application can display time and spectrum at the same time. Perhaps it helps to see the differences even better.
I've picked the phases from 0-100% from left to right in 10% increments.


This post has been edited by Kees de Visser: Dec 16 2008, 21:33
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bandpass
post Dec 17 2008, 08:21
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QUOTE (2Bdecided @ Dec 15 2008, 20:42) *
IIRC there's a comment by Brian Moore that temporal pre-masking decreases greatly with training, making the pre/post difference even more stark. Something like 3ms vs 20ms for a masker/maskee combination, but that's from memory - I've lost the paper.
Yes, I remember reading that somewhere too. Bit reluctant to try it myself though--don't want to end up hearing more artefacts! I daresay the actual masking periods are very signal dependent, filtered clicks being one of the most provocative cases.

QUOTE (Kees de Visser @ Dec 16 2008, 17:34) *
The iZotope RX application can display time and spectrum at the same time. Perhaps it helps to see the differences even better.
I've picked the phases from 0-100% from left to right in 10% increments.

Nice display. For the hell of it, I've redone my time-domain display above as an animated gif.

Does anyone fancy extracting the nuggets from this thread to a wiki entry?

-bandpass
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2Bdecided
post Dec 17 2008, 10:46
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QUOTE (Kees de Visser @ Dec 16 2008, 18:34) *
That's a beautiful graph, but only the centre one is linear phase - not all of them, as first words of the text imply.

Cheers,
David.
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Kees de Visser
post Dec 17 2008, 12:01
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QUOTE (2Bdecided @ Dec 17 2008, 10:46) *
only the centre one is linear phase - not all of them, as first words of the text imply.
Thanks for pointing that out. It has been corrected.
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Arnold B. Kruege...
post Dec 17 2008, 13:42
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QUOTE (2Bdecided @ Dec 16 2008, 10:53) *
Ah, so we come to the question of what the filter is supposed to be doing, and whether a sharp cut off is more important than the avoidance of ringing.

That depends on the application. The point is whether the brick wall filter introduces audible ringing. You stated that it did not. So while you suggest I'm assigning a "zero cost" to the gentle cut off, you are assigning a "zero cost" to the ringing.


No, I'm saying that there are two costs that need to be balanced - balance the cost of ringing to the cost of having more audible noise.

QUOTE
In truth, both have a cost - judging which is preferable is a matter for the designer, and application specific.


Check the title of the thread - the application is "Mastering Captured Vinyl For CD".

QUOTE
However, that's was not your original point at all: you implied that ringing is a "zero cost" problem because you believe there is no ringing, and if there is, it isn't audible.


Apparently you haven't kept up with my recent recantation of that position.

What I've learned so far is that it would probably be a good thing if we had filtering tools for vinyl mastering to CD that were based on linear phase filters, or better yet filters that were tipped a bit from linear phase towards minimum phase so that the ringing receives maximum temporal masking.

It further appears that said tools might benefit from variable slope features so that a subjective trade-off could be made to balance noise and ringing.

I know of no such tools on the market today, but it appears that they would be feasible to develop.

Voila: a product opportunity.
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2Bdecided
post Dec 17 2008, 14:26
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QUOTE (Arnold B. Krueger @ Dec 17 2008, 13:42) *
Apparently you haven't kept up with my recent recantation of that position.
Well, it is a little difficult to keep up with your position on anything...

QUOTE (Arnold B. Krueger @ Dec 15 2008, 14:59) *
In terms of temporal dispersal, the linear phase filter seems to have reduced temporal dispersal, even as compared to the original wave.
QUOTE (Arnold B. Krueger @ Dec 16 2008, 11:14) *
Comparison with the original wave is invalid because it has a vastly different frequency response.


QUOTE (Arnold B. Krueger @ Dec 16 2008, 11:14) *
I think we may need to review the purpose of the exercise. We are trying to filter out HF noise as effectively as possible with minimal effect on SQ.
QUOTE (2Bdecided @ Dec 16 2008, 12:20) *
We were, but we've moved on a long way from the original question. We're in the audible range now, for one thing.
QUOTE (Arnold B. Krueger @ Dec 16 2008, 15:03) *
We always were in the audible range, when we're talking effective filters in the middle of the frequency range of most sensitive human hearing.
QUOTE (Arnold B. Krueger @ Dec 17 2008, 13:42) *
Check the title of the thread - the application is "Mastering Captured Vinyl For CD".

Quitting now, before the forum quote bug strikes!

This post has been edited by 2Bdecided: Dec 17 2008, 14:29
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2Bdecided
post Dec 17 2008, 14:44
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QUOTE (Arnold B. Krueger @ Dec 17 2008, 13:42) *
What I've learned so far...
I was hoping what you've learnt so far is that brick wall filters ring, the ringing can be audible and objectionable, and it can be dramatically reduced by making the filters less brick-wall like.

You know, all the stuff that some of us were saying from page one wink.gif

QUOTE
...is that it would probably be a good thing if we had filtering tools for vinyl mastering to CD that were based on linear phase filters, or better yet filters that were tipped a bit from linear phase towards minimum phase so that the ringing receives maximum temporal masking.

It further appears that said tools might benefit from variable slope features so that a subjective trade-off could be made to balance noise and ringing.

I know of no such tools on the market today, but it appears that they would be feasible to develop.

Voila: a product opportunity.
Making the filters more gentle, rather than fiddling with the phase response, is the dramatically preferably solution unless the transition from objectionable noise to wanted signal is extremely localised spectrally.

This isn't the case with Vinyl: brick wall filters are pointless here. It's not even the case with 78s or tapes - the noise is broadband, while the signal level reduces (somewhat gently) at high frequencies. If any filtering is appropriate, it's gentle filtering. Brick wall filtering is not only pointless in this instance, but the associated audible ringing will be triggered by any transient (or worse still, impulsive) content in the recording. Do you think a recording from vinyl or shellac might contain any impulsive signal elements? smile.gif


As for a product opportunity: Yes.

However, Cool Edit Pro has had the FFT filter for over a decade - you can dial in as sharp or as gentle a filter as you wish. You cannot change the phase, but since the ringing is inaudible with a reasonably gentle filter, it would be of no great benefit there.

For the people trying to filter out spectrally localised noise (e.g. 15.625kHz squeak, 50/60Hz hum), shifting the phase would be beneficial. Though there can be better ways of defeating both of those issues, depending on the exact interference.


I daren't mention that one product opportunity appears to be in brick wall filters for CD upsampling. The top end of the market appears to be moving / have moved from brick wall to gentle, and from linear phase towards minimum phase. The difference "should" be inaudible, yet in A/B (not ABX) tests, the preference for these inaudible filters matches the preference for audible filters demonstrated in this thread - closer to minimum than linear phase; more gentle than brick wall.

I'm not claiming anything. Just pointing out the "co-incidence".

Cheers,
David.
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Kees de Visser
post Dec 19 2008, 23:37
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QUOTE (2Bdecided @ Dec 17 2008, 14:44) *
The difference "should" be inaudible, yet in A/B (not ABX) tests, the preference for these inaudible filters matches the preference for audible filters demonstrated in this thread - closer to minimum than linear phase; more gentle than brick wall.
So, do we have the courage (after 3 pages of warming up) to design a test to find out if >20kHz brick wall filter artifacts can be audible ?
I'd be surprised if tests like this have not been done before, so perhaps we can learn from them.
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