Seeking Advice on Improving FIR Filters for 4-Way Stereo System

[omousis]

Dear all,

I’m still learning the ropes when it comes to creating effective FIR filters for my 4-way stereo system. Unfortunately, the filters I’ve designed so far don’t sound as good as some older FIR filters that friends have uploaded to my system. I suspect the issue lies in my preparation process.

Below, I have included screenshots to provide more context:

1. Parameters chosen in the Correction Procedure Designer.
2. Measurements with the chosen target curve and the corrected measurements.
3. Target curve and corrected measurements only.

From these, I’ve noticed a few things:

• The target curve and the corrected measurements are significantly lower than the measurements. Specifically, they are almost 20 dB lower compared to the bass and upper midrange, and 10 dB lower compared to the lower midrange. While I don’t think this is the sole cause of the poor sound quality, it might contribute to the subpar results.
• Another concern is the size of the generated FIR correction filter. My filter is about 4 MB, whereas the ones I’ve used successfully in the past are over 100 MB. This seems like a potential issue.

Does anyone know the typical size of an FIR filter generated with AL? Could this size difference be impacting the sound quality?

Many thanks for your interest and insights!

Best regards,
Olivier

 

[omousis]

I noticed that the size of the FIR filter appears to be standard, so there doesn't seem to be an issue at this stage. The zip file sent to Roon contains one WAV file and two CFG files, whereas the older one generated by Acourate includes eight WAV files and two CFG files. Could this discrepancy be the source of a problem?

Olivier.

 

[juicehifi]

First bit is to be 100% certain that your measurements are ok. Two, maybe three things are required. 1) If your audio devices create glitches in the audio streams, the ttd correction will suffer. 2) If your measurement microphone isn’t properly calibrated it is very difficult to dial in on the best voicing. 3) If you measure at such a loud level that tour speakers are strained when they play the sweeps.

If you’re past that, more specifics about the sound quality would be helpful.

With a good mrasurement you can pretty much voice the sound to your preferences. And the only thing after that might be left to improve then would be transparency. But I have reason to believe that Audiolense is on top in that department. So hang in there. Trust the app, but be diligent about measurement quality.

 

[omousis]

Hi Bernt,

Thank you for your useful suggestions. Could you kindly clarify what you mean by the possibility that my audio devices might be causing glitches in the audio streams?In any case, I will revisit the measurements. You’re right; I’ve been conducting them at a relatively high level. Perhaps lowering the volume could help—I do hear some distortion of the sweep on one channel. I’m using the Beyerdynamic MM1 with its calibration files for the measurements, and I don’t believe the issue lies there. I’ll share updates on the forum soon!

 

[omousis]

I attempted to take additional measurements under more appropriate conditions, aiming to avoid saturation. Unfortunately, this did not improve the quality of the correction. Below, I have included the impulse response of my system; I'm not sure if it will help identify any issues with the measurements. Thank you for your assistance!

 

[juicehifi]

Nothing stands out as wrong with the impulses.

Does the timing difference between the tweeters look OK? And do you get similar timing on the tweeters from measurement to measurement?

And ... what is it that you don't like with the sound?

 

[omousis]

Thanks for your question, Bernt! Below, I have included the impulse response corrected for the tweeters. I noticed about a 0.4 ms delay between the left and right channels, which I assume is acceptable since it's under 1 ms.

The second plot shows the step response simulation and result. This one seems to deviate significantly from the shape shown in the Audiolense Help document. Could this indicate an issue at this stage?

The difference compared to the previous FIR filter created by my friend using Accourate is quite noticeable: the sound feels fuzzy, less focused, and lacking definition in the treble. I suspect I've made a mistake somewhere—could it be related to pre-ringing?

Looking forward to your thoughts! Thanks!

 

[omousis]

I also attach the FIR filter generated with AL. It is inserted in Roon...

 

[juicehifi]

Fostex? I'm guessing comppression driver here. With horn loading too maybe?

The tweeter corrections do not look optimal. I'm sure there are better ways.

I could look at your measurement file and see what can be done if you put it up here.

 

[omousis]

Please find the measurement file here: https://drive.google.com/drive/folders/1MibKVSZgAtweb_baM_VDkOXslEgJwmpA?usp=drive_link

The Fostex T925 correspond to the treble channel. A 2" Beyma compression is used for the upper midrange... The lower mid-range is 15-20dB lower than the other channels... May be it is part of the problem?

Thanks,
Olivier.