IPB

Welcome Guest ( Log In | Register )

Best kind of digital EQ filter?, FIR or IIR? Linear phase or minimum phase?
Best kind of digital EQ filter?
You cannot see the results of the poll until you have voted. Please login and cast your vote to see the results of this poll.
Total Votes: 27
Guests cannot vote 
Joe Bloggs
post Nov 7 2013, 17:06
Post #1





Group: Members
Posts: 375
Joined: 29-September 01
Member No.: 55



An audio company that I have some influence over is designing a new digital audio player and programming the digital EQ section. Their engineer told me that they're implementing it as an FIR filter. They're planning to play back hi-res music files up to 192k/24b on a somewhat dated SoC. I see two potential problems:

1. 192000Hz audio requires a LOT of taps in an FIR filter to get at the low frequencies. Frequency resolution is calculated as (Fs/N(taps)), so even a 2048 tap FIR filter can only get down to 100Hz or so. Not much of a bass boost filter, more like a midbass bloat effect.
2. The company director was also complaining of "phase shift" with digital filters. Now as you may know, corrective EQ filters are best implemented as minimum phase filters to cancel out the phase shift introduced by the headphones themselves, but FIR filters tend to be implemented as linear phase. However linear phase looks better on paper and sounds better to... somebody?

I suggested that they change the design to a minimum phase IIR filter, but the engineer said "isn't FIR supposed to be higher fidelity?" Where I have yet to get his word on what this "higher fidelity" entails.
I searched and found this:
http://www.dspguru.com/dsp/faqs/iir/basics
1.4 What are the advantages of IIR filters (compared to FIR filters)?

IIR filters can achieve a given filtering characteristic using less memory and calculations than a similar FIR filter.

1.5 What are the disadvantages of IIR filters (compared to FIR filters)?

They are more susceptable to problems of finite-length arithmetic, such as noise generated by calculations, and limit cycles. (This is a direct consequence of feedback: when the output isn't computed perfectly and is fed back, the imperfection can compound.)
They are harder (slower) to implement using fixed-point arithmetic.
They don't offer the computational advantages of FIR filters for multirate (decimation and interpolation) applications.

Now, I suspect that neither of the first two disadvantages apply, since they told me they're implementing their existing filter using 64-bit arithmetic. That sounds like plenty enough accuracy, and 64-bit has got to be floating point, I guess?

But what does the last point mean?

And can someone offer me some examples of how much more noise / distortion an IIR filter would generate compared to an FIR filter given the same bit precision in calculations?
Go to the top of the page
+Quote Post
 
Start new topic
Replies
Alexey Lukin
post Nov 9 2013, 22:34
Post #2





Group: Members
Posts: 206
Joined: 31-July 08
Member No.: 56508



I don't get the question. There's no Hilbert transform in RMAA.
Go to the top of the page
+Quote Post
saratoga
post Nov 9 2013, 23:00
Post #3





Group: Members
Posts: 5148
Joined: 2-September 02
Member No.: 3264



QUOTE (Alexey Lukin @ Nov 9 2013, 17:34) *
I don't get the question. There's no Hilbert transform in RMAA.


No there isn't. I had to use matlab's because I couldn't figure out how to get RMAA to show me any phase information at all.
Go to the top of the page
+Quote Post
Alexey Lukin
post Nov 10 2013, 08:56
Post #4





Group: Members
Posts: 206
Joined: 31-July 08
Member No.: 56508



QUOTE (saratoga @ Nov 9 2013, 18:00) *
No there isn't. I had to use matlab's because I couldn't figure out how to get RMAA to show me any phase information at all.

Why would you need a Hilbert transform to measure phase? You just need an FFT of the impulse response for that. If I recall correctly, RMAA does it for you: it displays phase and group delay graphs when the “Impulse/Phase” test finishes. Is it not the case for you?
Go to the top of the page
+Quote Post

Posts in this topic
- Joe Bloggs   Best kind of digital EQ filter?   Nov 7 2013, 17:06
- - Alexey Lukin   The last point refers to sampling rate conversion,...   Nov 7 2013, 17:20
- - saratoga   This is what we based the EQ in rockbox on: http:...   Nov 7 2013, 17:28
- - Alexey Lukin   I would not say that linear-phase EQs are better, ...   Nov 7 2013, 18:02
|- - saratoga   QUOTE (Alexey Lukin @ Nov 7 2013, 13:02) ...   Nov 7 2013, 18:46
|- - Joe Bloggs   QUOTE (saratoga @ Nov 8 2013, 01:46) QUOT...   Nov 7 2013, 19:01
|- - saratoga   QUOTE (Joe Bloggs @ Nov 7 2013, 14:01) QU...   Nov 7 2013, 19:39
|- - Ethan Winer   QUOTE (Joe Bloggs @ Nov 7 2013, 13:01) 1....   Nov 7 2013, 20:05
|- - mynameismeech   QUOTE (Ethan Winer @ Nov 7 2013, 14:05) T...   Dec 4 2013, 09:09
- - DVDdoug   I know a little about DSP (I have a couple of DSP ...   Nov 7 2013, 19:12
|- - Alexey Lukin   QUOTE (DVDdoug @ Nov 7 2013, 14:12) There...   Nov 7 2013, 19:26
- - Alexey Lukin   A 32-bit FP format does not always have sufficient...   Nov 7 2013, 19:30
- - extrabigmehdi   I've once used the vst plugin analyser by chr...   Nov 7 2013, 19:43
|- - saratoga   QUOTE (extrabigmehdi @ Nov 7 2013, 14:43)...   Nov 7 2013, 19:54
|- - extrabigmehdi   QUOTE (saratoga @ Nov 7 2013, 18:54) A gr...   Nov 7 2013, 23:40
- - Joe Bloggs   So the advice for the engineer, if he has 64 bit f...   Nov 7 2013, 20:03
- - sshd   2048 FIR taps is not a lot. I am using 6-channel ...   Nov 8 2013, 11:14
- - markanini   Theres a killer test I stumbled upon that involves...   Nov 8 2013, 12:33
|- - extrabigmehdi   QUOTE (markanini @ Nov 8 2013, 11:33) FIR...   Nov 8 2013, 12:51
|- - markanini   QUOTE (extrabigmehdi @ Nov 8 2013, 12:51)...   Nov 8 2013, 13:04
|- - extrabigmehdi   QUOTE (markanini @ Nov 8 2013, 12:04) QUO...   Nov 8 2013, 14:08
|- - markanini   Another case for minimum phase; Ask any pro mixing...   Nov 8 2013, 15:59
- - 2Bdecided   QUOTE (Joe Bloggs @ Nov 7 2013, 17:06) An...   Nov 8 2013, 12:37
|- - saratoga   QUOTE (2Bdecided @ Nov 8 2013, 07:37) QUO...   Nov 8 2013, 18:30
|- - Alexey Lukin   QUOTE (saratoga @ Nov 8 2013, 13:30) 1) ...   Nov 8 2013, 21:42
|- - xnor   QUOTE (Alexey Lukin @ Nov 8 2013, 22:42) ...   Nov 10 2013, 17:30
|- - Alexey Lukin   QUOTE (xnor @ Nov 10 2013, 12:30) QUOTE (...   Nov 10 2013, 18:30
|- - xnor   QUOTE (Alexey Lukin @ Nov 10 2013, 19:30)...   Nov 10 2013, 20:38
|- - Canar   QUOTE (Alexey Lukin @ Nov 10 2013, 10:30)...   Dec 4 2013, 19:14
- - knutinh   I would be sceptical about an "audio engineer...   Nov 8 2013, 21:37
|- - Alexey Lukin   QUOTE (knutinh @ Nov 8 2013, 16:37) I bel...   Nov 8 2013, 21:51
|- - saratoga   Did RMAA remove phase/impulse response testing? I...   Nov 9 2013, 20:31
|- - knutinh   QUOTE (Alexey Lukin @ Nov 8 2013, 21:51) ...   Nov 9 2013, 22:55
|- - saratoga   QUOTE (knutinh @ Nov 9 2013, 17:55) I don...   Nov 9 2013, 23:16
||- - knutinh   QUOTE (saratoga @ Nov 9 2013, 23:16) QUOT...   Nov 10 2013, 12:07
||- - Joe Bloggs   QUOTE (knutinh @ Nov 10 2013, 19:07) QUOT...   Nov 10 2013, 13:53
||- - Alexey Lukin   QUOTE (knutinh @ Nov 10 2013, 07:07) I do...   Nov 10 2013, 14:15
||- - knutinh   QUOTE (Alexey Lukin @ Nov 10 2013, 14:15)...   Nov 10 2013, 21:15
||- - saratoga   QUOTE (knutinh @ Nov 10 2013, 16:15) 1. S...   Nov 10 2013, 21:24
||- - knutinh   QUOTE (saratoga @ Nov 10 2013, 21:24) The...   Nov 11 2013, 10:50
||- - saratoga   QUOTE (knutinh @ Nov 11 2013, 05:50) QUOT...   Nov 11 2013, 23:09
|- - Alexey Lukin   QUOTE (knutinh @ Nov 9 2013, 17:55) I don...   Nov 10 2013, 08:53
- - extrabigmehdi   Well , markanini was previously discussing about h...   Nov 9 2013, 01:22
|- - markanini   QUOTE (extrabigmehdi @ Nov 9 2013, 01:22)...   Nov 9 2013, 09:21
|- - extrabigmehdi   QUOTE (markanini @ Nov 9 2013, 08:21) Exc...   Nov 9 2013, 12:18
- - Joe Bloggs   Can we have a show of hands among the experts on t...   Nov 9 2013, 15:39
- - bandpass   There isn't a best kind. The product's de...   Nov 9 2013, 19:33
- - saratoga   If its mobile iir is absolutely the right way to g...   Nov 9 2013, 19:53
- - Alexey Lukin   RMAA never displayed an impulse response, only a f...   Nov 9 2013, 21:11
|- - saratoga   QUOTE (Alexey Lukin @ Nov 9 2013, 16:11) ...   Nov 9 2013, 21:25
- - Alexey Lukin   Ah, yes, that test displays phase response and sav...   Nov 9 2013, 21:53
- - saratoga   Is there a way to get it to display the phase resp...   Nov 9 2013, 21:59
- - Alexey Lukin   I don't get the question. There's no Hilbe...   Nov 9 2013, 22:34
|- - saratoga   QUOTE (Alexey Lukin @ Nov 9 2013, 17:34) ...   Nov 9 2013, 23:00
|- - Alexey Lukin   QUOTE (saratoga @ Nov 9 2013, 18:00) No t...   Nov 10 2013, 08:56
|- - saratoga   QUOTE (Alexey Lukin @ Nov 10 2013, 03:56)...   Nov 10 2013, 18:35
- - Alexey Lukin   Hmm, it could have been pulled from the recent ver...   Nov 10 2013, 18:57
|- - saratoga   QUOTE (Alexey Lukin @ Nov 10 2013, 13:57)...   Nov 10 2013, 21:21
- - Alexey Lukin   Can you post these impulses as WAV files? Looking ...   Nov 10 2013, 21:09
- - Alexey Lukin   2. Yes, it would be numerically identical, albeit ...   Nov 10 2013, 21:21
|- - knutinh   QUOTE (Alexey Lukin @ Nov 10 2013, 21:21)...   Dec 4 2013, 09:37
- - xnor   QUOTE (Alexey Lukin @ Nov 10 2013, 22:09)...   Nov 10 2013, 21:36
- - Alexey Lukin   Thanks. I'm wondering if this is universal or ...   Nov 10 2013, 22:58
|- - knutinh   QUOTE (Alexey Lukin @ Nov 10 2013, 22:58)...   Nov 11 2013, 11:49
||- - Alexey Lukin   QUOTE (knutinh @ Nov 11 2013, 06:49) What...   Nov 11 2013, 20:34
||- - saratoga   QUOTE (knutinh @ Nov 11 2013, 06:49) I di...   Nov 11 2013, 23:11
|- - xnor   QUOTE (Alexey Lukin @ Nov 10 2013, 23:58)...   Nov 11 2013, 15:02
|- - Alexey Lukin   QUOTE (xnor @ Nov 11 2013, 10:02) No that...   Nov 11 2013, 20:29
|- - xnor   QUOTE (Alexey Lukin @ Nov 11 2013, 21:29)...   Nov 11 2013, 22:30
|- - Alexey Lukin   QUOTE (xnor @ Nov 11 2013, 17:30) How did...   Nov 12 2013, 08:56
- - Alexey Lukin   I don't know if any closed-form expression exi...   Dec 4 2013, 22:17


Reply to this topicStart new topic
1 User(s) are reading this topic (1 Guests and 0 Anonymous Users)
0 Members:

 



RSS Lo-Fi Version Time is now: 19th December 2014 - 21:46