Article: Calibrating Desktop Speakers using Focus Fidelity Filter Designer

[Focus Fidelity]

On 3/5/2021 at 10:10 PM, Confused said:

@mitchco - A fascinating article.  I have to admit that the very concept of "room correction" for desktop speakers had never occurred to me, but it seems obvious now it is out there!  Thanks for writing this.

 

You mention at the start of the article that correction for a desk top set up is "highly demanding", and the ultimate conclusion is that the Focus Fidelity software did a good job.  Can it be extrapolated from this you would recommend Focus Fidelity for a conventional (not desktop) hifi set up?

 

I have spent quite a bit of time with REW, and have obtained reasonable results, but I always feel it would need a LOT more time and effort to get everything "just so".   Is Focus Fidelity a better option than REW, in terms of results obtained versus time invested? 

 

I am planning to make some changes to my room, which will include some room treatments etc., so it would be great to have some (reasonably) user friendly software to assist with periodic updates.  I know this stuff will never be easy, it does take effort to move along the learning curve, but any software that might help just a little has to be of interest.

 

Hi @Confused Our software is intended for conventional Hi-Fi layouts and we expect this to be the most common use case.

Once you have a set of measurements and are familiar with our software you'll find it only takes a few minutes to make adjustments and generate a new filter.

 

Kind regards,

David

[Focus Fidelity]

Hi @Confused,

 

Yes, a dedicated module for performing measurements will be released but is likely several months away. This will have a workflow that makes it easy to perform measurements of multiple speakers in multiple positions. All settings will have suitable default values and a good step by step user guide will be included. It'll be tested thoroughly with the UMIK-1, UMIK-2 and a Dayton EMM-6 plus USB audio interface.

 

If you're up and running doing measurements with REW then I think you'll find the learning curve with the filter design software straight forward and you should be generating filters within an hour by following the user guide https://www.focusfidelity.com/FFDManual.pdf

 

Kind regards,

David

 

[Focus Fidelity]

1 hour ago, dm68 said:

Hi Mitch, great article. I bought a license. I'm intending to use the filters with HQPlayer which requires seperate filters for the left and right channels. I can't for the life of me work out how to export the filters for the seperate channels. Any help would be much appreciated.

Hi @dm68 The filters are exported as stereo *.wav files so both channels in one file. There is no feature right now to export as mono *.wav files. I can however add this as a feature if needed.

[Focus Fidelity]

On 5/10/2021 at 8:44 PM, Confused said:

I am just trying to improve my own understanding of how this software works, so apologies if these are basic questions.

 

Looking at the Focus Fidelity website, it shows this for the target response:

 

 

In the above example, for the frequencies between 100Hz and 1000Hz, the majority of the in room measured response is below the target line.  So what does the software do here in terms of frequecy SPL correction?  Does it ignore this region or does it provide a "boost" to these frequencies?  From my limited experiments with REW creating relatively crude PEQ type correction, you essentially cut the peaks above the line but any "boosting" below the line is either ignored, or at least severely limited. 

 

In the above example, I can see that the peak at 50Hz or could be easily corrected, as could the peak at about 10kHz, it is just the 100Hz to 10000Hz zone that puzzles me.  Maybe I am misunderstanding how the target works?

 

Hi,

 

It will apply boost when the measured frequency response is below the target, the maximum amount of boost is adjustable (on the filter magnitude page). I should also point out that the software determines which dips/notches are not minimum phase and limits to the boost to those areas even further. This gives a more optimal result in the time domain.

 

[Focus Fidelity]

15 hours ago, Confused said:

Thanks for the response.  

 

This makes me wonder, I note the software includes phase corrections.  So where you have minimum phase induced dips / nulls (particularly in the bass region) do these phase corrections serve to mitigate the these dips / nulls (in terms of frequency vs SPL) , at least in part?

The software focuses on attenuating resonant modes and improving time domain criteria (ringing, step response, excess phase). Boosting a sharp dip/notch will result in a filter with significant ringing (pre or post depending on if the dip is minimum or maximum phase) so the software will seek to largely ignore the dip.  The relationship between phase, time domain and magnitude response gets rather complex and mathematical quickly.

[Focus Fidelity]

If the dip is minimum phase it will apply boost (gain) with matching phase shift to improve both the frequency response and impulse response.

[Focus Fidelity]

15 hours ago, Confused said:

OK, so the phase shift should have some positive impact on frequency response.  (I guess this will be room / case dependent to a degree)

 

Anyway, I feel that I have been laboring this point a little, so apologies for that, but I am just trying to get a better understanding of mechanisms involved here.  Ever curious.

 

For what it's worth, I have pretty much decided to buy the software and give it a try.  The only thing stopping me is that I am busy with other projects in the short term, no point buying software and not having time to use it, but I should get there in a couple of weeks or so.

It's fairly complex, some of the relevant math https://en.wikipedia.org/wiki/Hilbert_transform

 

Time domain performance is the end goal really, an example showing a waterfall plot and step response can be found here https://www.focusfidelity.com/solutions

[Focus Fidelity]

14 hours ago, Confused said:

I had a few plans for last weekend that were all basically abandoned due to very wet weather in the UK.  So finding myself with a little unexpected free time, I decided I would re-measure my room using REW, and with that done buy myself a copy of the Focus Fidelity Filter Designer software.  

 

I suspect that anyone who follows the topic of room correction on this forum will acknowledge that Mitchco is an expert in this field, by contrast, I am not. 

 

So when I read Mitcho's article regarding Focus Fidelity Filter Designer and he states that the software is "easy to use", I did kind of think in my head "yes, for you maybe, but I bet I'll get stuck somewhere".  The point being, that I can of many time in my life when I have tried some new software package and have found myself wasting hours on end wondering why it does not work as it should.  Maybe a bug somewhere, some odd setting that I have not got right, unexplained weird results, this kind of thing.  I have a fear of new software, which I see as route to frustration and hours of free time wasted.

 

So having sorted out some new REW measurements, I took the plunge and purchased the Filter Designer software.

 

Completely new to the software, I ran trough the instructions in the manual, step by step.  Where default settings were available, I simply kept with the defaults, I just wanted to see if I could get this thing working.  Anyway, within about one hour of starting the download for the software package itself, I had created a zip file for my convolutions, loaded them into Roon and had music playing.  I was actually expecting to hit a few issues and problems, but no, the software did it's stuff and everything seemed to work as it should. 

 

With a quick listen, I was not that happy with the result, I had just used the automatically generated target curve, and the tonal balance did not sound right at all to my ears.  To be honest, I was just pleased I had got everything working.  So, a second attempt, this time making some minor adjustments in the target frequency curve editor.  The results were better, this was moving in the right direction, but it still did not sound as I had hoped.  Then a third attempt, a bit more fine tuning of the target curve, this was much better.

 

After that, I just sat down and listened to selection of music.  Everything sounded good, from acoustic stuff, to rock, to electronica.  The main difference is a simple step forward in clarity, the effect is remarkable.  Sound that is a little muddled and irritating is replaced by music.  Maybe when people talk about "digititis" what they are actually suffering is "roonititis", but this is the effect, music sounds less reproduced by digits and more real.  Improvements in sound staging were obvious, the speakers become a less obvious source of the sound, moving towards invisibility, and a definite step up in clarity.  As a bit of an aside, I use a Devialet amp, which perhaps unusually these days has tone controls.  In the past, I have pretty much found the bass control to be useless in practical terms.  OK, it works, but if you happen to listen to an album that is inherently bass light, think of the classic "80's CD sound", then adding bass gain often just makes things sound worse, it just adds mud to the sound and sounds wrong.  Running the Focus Fidelity convolutions, suddenly the bass control does what it should, you add bass gain, you get more bass, clear bass.  I think this is clearly indicative of how Focus Fidelity is "cleaning" the sound of the system in the room

 

I was worried that would would struggle to get anywhere with this software, but it basically took my one Sunday morning from scratch to get a result that I was pleased with, and I am a room correction novice.  

 

I am sure that I still have a lot to learn, and I am also sure that I can improve on this early result.  The good thing is that the software is quick and easy to use, so I am happy that once I have had some time to listen more to the convolutions that I have, I will be able to investigate some of the settings in more detail, it should be easy to "fine tune", create new convolutions, and experience the results for myself.  This is where I think this software will be invaluable to myself.  Room correction is very complex topic, but there is nothing to beat being able to fine tune some parameter or another, and within a few minutes being able to listen to the results for yourself.

 

To be clear, the hardest part of this entire process was getting the actual measurements made in REW.  So I would say that for anyone who is at a level where they can perform the required REW measurements, using Focus Fidelity Filter Designer should be relatively simple, it is far more intuitive than REW.

 

It is very early days for myself, I have a lot to learn, a lot to investigate and try, but this is a great tool to start the convolution journey.  The fact that someone like myself can get good results in one rainy Sunday morning perhaps tells you all you need to know. 

 

Being in the UK the cost of the software worked out at £185.  Based on my experience of the software so far, this is £185 well spent and an absolute bargain in audiophile terms.

 

I also note that at the time of writing only 7 people are following this thread, whereas you get hundreds of followers following other "tweaker" threads.  Seems a shame, as there are some very real benefits to sound quality available here, for those will to make the effort.

Hi,

 

Thanks for taking the time to share your experience in detail.

Tweaking the target curve is to be expected in general, while the initial target is a best fit through the measurement data it can still also be a large change from what you might be used to or simply not be what you prefer.

If you do find yourself with any questions or have anything you'd just like doubled checked simply e-mail your project file to the Focus Fidelity support e-mail address.

 

Kind regards,

David

 

[Focus Fidelity]

3 hours ago, MagnusH said:

I know of one very good reason for export to two mono convolution files: HQPlayer. I use that for its filters (I recommend it strongly), but also for its excellent DSP/convolution engine. However, it only accepts 2 mono files for convolution (as far as I know).

Hi @MagnusH You can now export the filters as two mono *.wav files. I have customers using this feature with HQPlayer.

[Focus Fidelity]

Focus Fidelity's freeware measurement tool is now available for download, https://www.focusfidelity.com/download

 

The user manual https://www.focusfidelity.com/ImpalaManual.pdf

is a step-by-step guide.

[Focus Fidelity]

Hi @dathzo With the Focus Fidelity software you can select how many measurement points you'd like to use in a project between 1 and 10. You can cluster the points tightly to cover 1 seat of wider spacing to cover a sofa for example depending on your application. So there is room for experimentation.

 

[Focus Fidelity]

Hi @dathzo Happy New Year to you as well. The current plan is some updates to the existing software followed by a Mac version. Crossovers etc will follow after that, I don't have a timeframe for those features right now.

[Focus Fidelity]

Hi @Confused  The target curve was based on the Harman target but with the bump around 600Hz added to preserve the "character" of the speakers being used.