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mkrzych

Short explanation/confirmation needed for digital filters

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Hello experts,

Maybe this question was asked several times, maybe not, but which digital filter has the most steepness: minimum phase, linear phase or apodizing in general? I see some doubts and discussion about this subject on the Internet. Also, is the roll-off done at the Nyquist frequency, so does it mean 48kHz if 24/96 is playing? This is to refresh my understanding of my DAC-R filters ;-)

 

I saw also some articles explaining that "apodizing" is similar to "windowing" and it may roll-off gently before the Fs/2, but for high resolution above 48kHz it could be the way to go?

 

Thanks in advance.

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Linear-phase filter can be very steep brickwall filter. Also it is possible to design very gentle roll-off linear-phase filter.

Similar level of steepness can be achieved also by minimum-phase filter. Also it is possible to design very gentle roll-off minimum-phase filter.

But (this is my understanding, it can be wrong) , minimum-phase filter cannot place zero on the unit circle of Z-plane therefore it cannot eliminate stopband signal completely, while linear-phase filter can place zero on the unit circle. Also I feel math is more difficult on designing minimum-phase filter :)

> Also, is the roll-off done at the Nyquist frequency,
> so does it mean 48kHz if 24/96 is playing

Basically yes. Practically there is no meaningful signal exists at 48000Hz of 96kHz PCM data, Typical Nyquist filter cut off frequency is 43200Hz ~ 45600Hz when fs=96kHz

Apodizing means some reduction of ringing of time domain, this means very steep brickwall filter is not possible. I'm not sure it is the way to go for everyone or not. You may choose any digital filter you liked the most by listening music using your DAC-R. Personally think the sound difference of digital filters is very small :)

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6 hours ago, mkrzych said:

Maybe this question was asked several times, maybe not, but which digital filter has the most steepness: minimum phase, linear phase or apodizing in general?

Both linear and minimum phase filters can produce any practical magnitude response. Where they differ is, as the names indicate, in the phase response. Apodizing filters are by definition slow roll-off.

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Many thanks guys for the explanation. Sure, at the end listening is the most important, but just wanted to refresh my understanding to be better prepared for listening ;-) If most of the filters cuts off above the 40kHz indeed, it could be very small difference (if audible at all) to them. In general what I have been noticed is using apodizing filter for high resolution content produce a bit open and deeper soundstage with more warm sound - quite like it, it depends also on the quality of the mastering and recording. 

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1 hour ago, yamamoto2002 said:

But (this is my understanding, it can be wrong) , minimum-phase filter cannot place zero on the unit circle of Z-plane therefore it cannot eliminate stopband signal completely, while linear-phase filter can place zero on the unit circle. Also I feel math is more difficult on designing minimum-phase filter :)

 

Both filters can have exactly same frequency response, only different phase response. That is the case with mine.

 

1 hour ago, yamamoto2002 said:

Apodizing means some reduction of ringing of time domain, this means very steep brickwall filter is not possible. I'm not sure it is the way to go for everyone or not. You may choose any digital filter you liked the most by listening music using your DAC-R. Personally think the sound difference of digital filters is very small :)

 

It means just replacing the original ringing with something else, shorter or longer. I have both... But more important effect is to reduce adverse effects of current ADC filters.

 

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47 minutes ago, mansr said:

Apodizing filters are by definition slow roll-off.

 

Not necessarily, for example the ESS one is "sharp" roll-off...

 

I do both, relatively slow ones and also extremely steep ones.

 

In fact the first apodizing filters were pretty steep. While many of the newer ones, like MQA are very slow roll-off and in fact likely don't anymore even function as apodizing filters because of that. (if a filter doesn't really filter anything it cannot do much either)

 

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9 hours ago, Miska said:

 

Both filters can have exactly same frequency response, only different phase response. That is the case with mine.

 

 

 

 

Thank you for your clarifying. I thought if minimum-phase filter eliminates some frequency signal completely, complimentary maximum-phase filter cannot recover the original signal because information is lost.

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20 hours ago, Miska said:

 

Not necessarily, for example the ESS one is "sharp" roll-off...

 

I do both, relatively slow ones and also extremely steep ones.

 

In fact the first apodizing filters were pretty steep. While many of the newer ones, like MQA are very slow roll-off and in fact likely don't anymore even function as apodizing filters because of that. (if a filter doesn't really filter anything it cannot do much either)

 

 

Thanks @Miska! It seems very dependable on the implementation, so in case of Wolfson WM8742, what is that?

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10 minutes ago, mkrzych said:

Thanks @Miska! It seems very dependable on the implementation, so in case of Wolfson WM8742, what is that?

 

That is one of the "original" and similar to the ESS one, so goes into "steep" category. If you can select filter, the Filter 5 is quite nice.

 

P.S. It is also one of the chips that has nice DSD Direct mode. Being a bit old it is just limited to DSD64.

 

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