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Audio-gd Digital Filter (flavor switch) for NFB5, NFB9, NFB10se, NFB3.1

post #1 of 32
Thread Starter 

 

Starting a new discussion for Audio-gd's digital filter which is also known as "flavor switch" for NFB5, NFB9, NFB10se, NFB3.1

Any comments / reviews and discussion is appreciated.

 

 

What's advantage of setting the digital filter characteristic:
Except the NOS DACs , all DACs have applied the digital filter, the digital filter characteristic effects the sound quality and flavors. Most DACs have the fixed digital filter characteristic maybe not the best taste for the users. The NFB-x have 9 types  digital filter characteristic for users find the best sound of personal sense.

 

 

Flavor button:
Select the oversampling and digital filter response of the NFB-9 .

Display 1 : 2X oversampling , Minimum phase 'soft-knee' filter. Up to 192KHz support.            3s.GIF
Display 2 : 2X oversampling , Linear phase 'soft-knee' filter. Up to 192KHz support.                         2s.GIF
Display 3 : 2X oversampling , Linear phase 'brickwall' filter. Up to 192KHz support.                         1s.GIF
Display 4 : 4X oversampling , Minimum phase 'soft-knee' filter. Up to 96KHz support.                      6s.GIF
Display 5 : 4X oversampling , Linear phase 'soft-knee' filter. Up to 96KHz support.                        5s.GIF
Display 6 : 4X oversampling , Linear phase 'brickwall' filter. Up to 96KHz support.                         4s.GIF
Display 7 : 8X oversampling , Minimum phase apodising filter. Up to 48KHz support.                    9s.GIF
Display 8 : 8X oversampling , Linear phase apodising filter. Up to 48KHz support.                         8s.GIF
Display 9 : 8X oversampling , Linear phase half-band filter for backward compatibility. Up to 48KHz support.                                                                                                            
                                                                                                                                             7s.GIF

 

 

As I know, the digital filter is built-in component of WM8741.

post #2 of 32

WM8741 digital filters. The presentation is slightly more open with filters 5 and 7 imo.

post #3 of 32
Thread Starter 

 

 

Thank you for the point out.

 

copy the article here -->

http://hifiduino.blogspot.com/2009/05/wm8741-digital-filters.html

 

WM8741 Digital Filters

 

One of the reasons I embarked to use Arduino to control the WM8741 DAC was because certain digital filters are only available thought the s/w interface. I've done some additional reading about these filters. The DAC has the following 5 selectable filters. The names of these filters are mentioned in a white paper and in the data sheet of the new WM8742. (The 8742, however seems to be a cost-efficient version of the older WM8741 which is spec'ed as having better signal to noise ratio). These filters are:

  1. Linear phase ‘soft knee filter’
  2. Minimum phase ‘soft knee filter’
  3. Linear phase brickwall filter
  4. Minimum phase apodising filter
  5. Linear phase apodising filter

Filter #3, the linear phase brickwall filter is the traditional/historical filter for digital audio. It is a steep filter right after 20 KHz and has been shown to produce a lot of pre and post ringing from an inpulse response. Wolfson indicates that this filter is to be used with other filters (from other components such as DSP chips) in the digital audio path. Filter #1 is the "slow roll off" filter that more modern DACs and CD players have used to remove some of the "digital hash" that have been observed in the past. The slow roll off filter reduces both the pre and post ringing of an impulse response. These two filters brickwall or fast roll-off and soft knee or slow roll-off have been the mainstay of digital audio reproduction for all these years.

Filter #2 is a new kind of digital filter. Whereas in the past audio engineers have insisted in phase linearity (meaning all frequencies have equal phase or delay), More recent research have shown that a "minimum phase" filter sacrifices some of the phase linearity (adds some phase distortion) for better time response. Specifically, minimum phase filters minimizes the pre-ringing of an impulse response. Audio researchers have argued that pre-ringing is an un-natural effect and therefore the ear is more sensitive to this kind of distortion. They have also argued that phase distortion is not very audible. This filter also incorporates soft-knee or slow roll-off and this reduces post ringing as well. The properties of this filter are similar to the "MP filter" found in Ayres latest CD player.

Here is a diagram depicting the impulse response in a linear phase filter and a minimum phase filter.

According to the Ayre white paper, adding the properties of slow roll-off filter to the minimum phase filter will decrease the post ringing, resulting in something like this:

Note that the axis are different, but in relation ot the first diagram, the second diagram shows no pre-ringing and much reduced post-ringing.

Conceptually, the Wolfson Minimum Phase soft-knee filter is the equivalent of Ayre's MP listen filter. Obviously the implementation is different and the relative quality of these filters have not been evaluated.

 

Filter 4 and 5 are only available through the s/w interface. "Apodising" ("Apodizing" in American English) filters have been equated to minimum phase filters and minimum phase filters with slow roll-off in the literature. But as the name of the filters in the Wofson DAC suggests, "apodizing" is an additional filter technique to that provided by minimum phase soft-knee.

The use of slow roll-off filters allows some of the higher frequency (beyond the Nyquist frequency) energy to be reflected back into the audio band. This is known as "aliasing" an is a source of distortion. An apodizing filter according to the Wolfson white paper, is one where the filter fully attenuates by Fs/2 (the Nyquist frequency) and thus they start attenuating earlier than Fs/2 often sacrificing flat requency response to 20KHz.


Filter #4 appears to combine the best qualities of these filters. "Minimum phase apodizing" signifies that pre-ringing is eliminiated, post-ringing reduced and aliasing distortion eliminated. As the Wolfson white paper indicates, no one filter is the perfect filter but a designer hopes to makes the best trade offs by using multiple filters.

Conceptually Filter #4, minimum phase apodizing filter, is what Meridian is using in their latest CD player.
Obviously the implementation is different and the relative quality of these filters have not been evaluated.

post #4 of 32
Thread Starter 

Some comments I found on Internet:

http://www.stevehoffman.tv/forums/archive/index.php/t-239298.html

 

"Try listening to some classical orchestral music and the differences between the filters should be a lot more obvious. For example, you should be able to observe the first violins sounding a bit more metallic and edgy with the minimum phase filter types but conversely the notes upon change of bow will also seem to start more decisively with a clearer "bite" to them and you will thus get a slightly better sense of the individual players making up the section (since the players being human, there is no such thing as all the players playing in perfect synchronisation, plus each violin / bow / string brand and type / player combination will sound different).

On the other hand, the linear filters, especially the soft knee should make the violins and woodwind sound a bit warmer and silkier, but also a bit more clouded in sound, with the starts of notes upon bow changes (in the case of the strings) being less clear and well-defined compared to the minimum phase filters. The linear filters may also make the individual contributions of each player less obvious.

In my opinion, the best combination of filtering would be the soft knee linear filter when used in conjunction with high resolution, high sample rate source material, whereas the minimum phase filters may in some circumstances provide a subjectively better sound with low resolution source material."

post #5 of 32

^ Interesting. Goes towards explaining why I keep going back to filters 5 and 7 on the 10SE.

post #6 of 32

According to King Wa 9 is the best Better technicaly my fav are 3, 6 , 9 , currently using 9 (for me 3 -6 sound almost the same , 9 just a bit different peraphs placebo after king wa said 9 is better biggrin.gif)  , i don't like at all 1 and 3  (highs too much roled off for my tastes)  

 

But switching filters with NFB-2 is not very convenient (jumpers ...) soo not the best to hear difference beetween filters but some are obvious like not liking at all 1 and 3 .

 

Edited : hum ok , i read it somewhere else , so if i am not wrong King Wa said that he personnaly prefered Filter 9 .


Edited by HaVoC-28 - 11/25/11 at 5:51pm
post #7 of 32

A lot people consider in audio world there is never have the best but the better. There is a subjective sense world.

 

If there are a best option on the WM8741, I think the manufactory maybe only offer the best performance issue rather than offer so lot options but without the level comments .

 

post #8 of 32


 

Quote:
Originally Posted by Kingwa View Post

A lot people consider in audio world there is never have the best but the better. There is a subjective sense world.

 

If there are a best option on the WM8741, I think the manufactory maybe only offer the best performance issue rather than offer so lot options but without the level comments .

 



Edited my post thanks for the clarification but i am not wrong in saying that you prefered filter 9 am i ? (my english si not perfect like your biggrin.gif , some misunderstood can happen) . And sorry if i said something wrong about filters frown.gif.

 

Every one just have to try and use the filter that he likes most soo .


Edited by HaVoC-28 - 11/25/11 at 6:01pm
post #9 of 32

There are some lot alterable factors affect the sense even though with same system.

The mood, happy, exciting, tired ect make different taste.

The recorders  aren't always have same flavor.

The temperature and humidity  affect the headphone and special the speakers.

The different components of the system make different sound flavors.

So I think the options addjust by the WM8741 is reasonable.

Once you can pick up the different sound of the setting, can choice different setting for the sounding you want.

post #10 of 32
Quote:
Originally Posted by Kingwa View Post

There are some lot alterable factors affect the sense even though with same system.

The mood, happy, exciting, tired ect make different taste.

The recorders  aren't always have same flavor.

The temperature and humidity  affect the headphone and special the speakers.

The different components of the system make different sound flavors.

So I think the options addjust by the WM8741 is reasonable.

Once you can pick up the different sound of the setting, can choice different setting for the sounding you want.



Ok thanks for the clarification never though about all this .

post #11 of 32
Thread Starter 

Some interesting discussion about apodizing filter here --> http://www.avguide.com/forums/apodizing-filters

post #12 of 32

Is it possible to get 4x oversampling Linear phase apodising filter (24/96 support) with the WM8741 chip?

post #13 of 32
For what I understand, our cd audio quality is recorded in 16bit, 48khz sampling only. So, I think filter it in 7,8,9 in 10SE would be better? We could filter in #1, 2 or 3 but the sound quality should be at 16bit only.

Am I correct to say that?
post #14 of 32


 

Quote:
Originally Posted by YoengJyh View Post

For what I understand, our cd audio quality is recorded in 16bit, 48khz sampling only. So, I think filter it in 7,8,9 in 10SE would be better? We could filter in #1, 2 or 3 but the sound quality should be at 16bit only.
Am I correct to say that?


CD =  44khz sampling , DVD = 48khz etc , try yourself wich is better :p 


Edited by HaVoC-28 - 12/9/11 at 3:59am
post #15 of 32
Quote:
Originally Posted by HaVoC-28 View Post



 


CD =  44khz sampling , DVD = 48khz etc , try yourself wich is better tongue.gif 

I think it would be the same if the audio quality is in 16bits. 44 vs 48khz should not be the huge different in kbps.

Unless the dvd you mentioned were recording in 24bit.
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