Wondering about convolution files

[tony22]

I’ve been toying with the idea of trying them out. I know and use REW, and have my room as well treated acoustically as I can manage, but there are still some discontinuities that I’d like to try addressing with convolution files. I ran REW’s EQ tool and looked over the filters, but one of the things that’s been on my mind is - are there limits to boosting in the digital domain like we have when doing EQ in the analog domain? I’m not sure. Say, for example, a convolution filter boosts +6dB at 60Hz (this is just an example). If it’s done in the digital domain, is there the same kind of risk to blowing out drivers / amps / etc as if it was done with (like) an old Audio Control C-101?

I’m a long time Minimserver user, so I’d enable the usage there. A little tweaky, but it doesn’t look too hard.

 

[GroovySauce]

I know just enough about using convolution filters to get myself (and others) into trouble.

4+ years ago was the last time I used any type of room correction software.

My experience was it was much better to lower peaks and not boost anything. I also found that a gentle touch was more pleasing that tweek everything to ruler flat. I was using HQPlayer.

+6 db boost is 4x the power. Even with a lot of headroom you can run into clipping issues depending on your setup.

If you have a suck out due to waves canceling at the listening position, adding more energy at that frequency isn't going to fix the problem.

 

[tony22]

My experience was it was much better to lower peaks and not boost anything. I also found that a gentle touch was more pleasing that tweek everything to ruler flat. I was using HQPlayer.

Yes, that’s kind of what I’ve concluded as well. My limited experience with DRC goes back to the earlier Squeezebox days, and Inguz.

If you have a suck out due to waves canceling at the listening position, adding more energy at that - frequency isn't going to fix the problem.

Yeah, I really can’t argue with that. More speaker movement planned, but there’s probably only so much i can do.

 

[ecwl]

I’ve been toying with the idea of trying them out. I know and use REW, and have my room as well treated acoustically as I can manage, but there are still some discontinuities that I’d like to try addressing with convolution files. I ran REW’s EQ tool and looked over the filters, but one of the things that’s been on my mind is - are there limits to boosting in the digital domain like we have when doing EQ in the analog domain? I’m not sure. Say, for example, a convolution filter boosts +6dB at 60Hz (this is just an example). If it’s done in the digital domain, is there the same kind of risk to blowing out drivers / amps / etc as if it was done with (like) an old Audio Control C-101?

There are two ways to do this. You can just add the +6dB at 60Hz digitally so what would happen is that if the music at 60Hz is already maxed out, it’ll simply digitally clip the signal which would create a distortion but generally won’t blow out the speakers. And of course you won’t actually get that +6dB boost because digitally the music signal was already maxed out at 60Hz. Alternatively, if you don’t want any clipping you can lower the entire digital signal by 6dB first and then you add that +6dB boost at 60Hz. That way there will be no clipping but then you would have to crank up your volume knob by 6dB to get the same volume. That’s the theory digitally…

in reality, if you have a 6dB dip at 60Hz in the room, it’s usually because there is a room mode null there. So cranking up the speaker volume at that frequency by 6dB would not cancel that null because the louder 6dB would bounce around the room and cancel itself out.

 

[ecwl]

Yeah, I really can’t argue with that. More speaker movement planned, but there’s probably only so much i can do.

So it is not that often where the speakers are sitting at a 60Hz null which is causing the 6dB dip. It would be much more often that your listening position is where the 60Hz null is which is causing the dip.

This is why usually, it's always recommended as GroovySauce said, to move the listening position first, instead of moving the speakers. Moreover, unless your speakers are on wheels, it's harder to move the speakers around.

The best thing to do is actually not to move anything first. Since you already have REW & a microphone, you should actually look at the possible positions you can put your listening seat. And then measure the frequency response of the listening position say 6" forward, 6" back 12" forward, 12" back, etc at ear level. Wherever you found the bass to be smoothest by looking at the graph in REW is where you want to move the sofa to.

Once you moved the listening position, you'll have to toe in and out of the speakers to make sure the midrange and treble balance and imaging remains the same as before.

Of course, if you have speakers on wheels, then it's relatively easy for you to afterwards keep the microphone now at the new listening position and then move the speakers forward and backwards by 6" at a time and see where the bass is smoothest. Once you've settled on that, you'll have to once again re-toe in and out the speakers until the imaging and midrange/treble balance is restored. I found that even though you can do the latter with the microphone too, it usually is much easier just to do it by ear. And then you can put the spikes/feet back onto your speakers.

In the past, I've found it impossible to determine bass peaks and nulls by ear since I'm not a seasoned pro with decades of experience. So I always use REW or other forms of RTA for that.

 

[tony22]

The best thing to do is actually not to move anything first. Since you already have REW & a microphone, you should actually look at the possible positions you can put your listening seat. And then measure the frequency response of the listening position say 6" forward, 6" back 12" forward, 12" back, etc at ear level.

Did all that. Many times. Also used REW’s Sim tool (and others) also many times to see what happens when things get moved around. I can get the center frequency of the dip to move around some, depending on what gets moved, and I can even bring it up by about 3dB (so far as indicated by simulation), but I can’t get rid of it completely and keep either the speakers or the seat in a reasonable location. I can get rid of it if I add a sub as a mode cancellation device, but I’d rather not do that… just yet.

 

[Zuman]

I've been thinking about the Schiit Loki Max eq as an alternative. The reviews I've seen have been very positive, and they've made it clear that they were trying to emulate the legendary Mark Levinson Cello Palette. I don't want to insert a new device and set of cables into my chain, but I haven't read anything where people who have used it have found a problem.

 

[ecwl]

Did all that. Many times. Also used REW’s Sim tool (and others) also many times to see what happens when things get moved around. I can get the center frequency of the dip to move around some, depending on what gets moved, and I can even bring it up by about 3dB (so far as indicated by simulation), but I can’t get rid of it completely and keep either the speakers or the seat in a reasonable location. I can get rid of it if I add a sub as a mode cancellation device, but I’d rather not do that… just yet.

I wouldn't trust the room simulator unless you found the room simulator results are identical to your current measurements. I personally have never seen a room simulator result to closely match a real physical room's measurements.

But if you've moved the microphone around and your current listening position is the best possible position for the bass, yeah, you're done. There really aren't a whole lot more you can do. I always think about everything I do in audio as a series of compromises, just like in life.

 

[jtcfdog]

I've been thinking about the Schiit Loki Max eq as an alternative. The reviews I've seen have been very positive, and they've made it clear that they were trying to emulate the legendary Mark Levinson Cello Palette. I don't want to insert a new device and set of cables into my chain, but I haven't read anything where people who have used it have found a problem.

I bought the Schiit Lokius just a week ago just hoping to tone down the strident upper mids in some recordings and it resides between the dac and pre.It does the job.It won't help issues with a room, but tiny adjustments can help with less than stellar recordings. I was concerned about the addition of another set of cables and yes I can hear the influence of the odd set that really don't belong.
I didn't have an extra set of ICs of the same brand (Voodoo)even though they are the same metal(silver).The odd set are ribbons (ZenWave) and fortunately I like the difference when the Lokius is set to bypass and when it is active.I tried a set of copper instead and it sounded very strange.If I had Voodoo throughout very possibly it would be transparent.Right now it's fun to play around with and I'm thinking about buying a professional unit in the future.

 

[Brucemck2]

I’ve used various DSP-based filters for years. A simple notch (or two or three) and basic shelving is easy to do in the DSP section of most playback software (via Roon, or adding a plug in similar to Fab Filter to J River). AFTER you’ve done what you can via speaker and listener placement, and room treatment, it can make a nice improvement. You’ll need to learn how to do before and after measurements as the simulators aren’t great.

Convolution files can improve things well beyond that (phase, timing alignment, etc.) but aren’t easy to dial in. As with turntable setup, years of experience makes a real difference. I’d highly encourage you using a third party to develop the filters based on measurements you provide to them:

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