I'm sharing the explanation of what I believe to be happening with this phase shuffling on my thread. I had mentioned trying it and using it and consider this thread to be mine so I don't spam others too much. Here I just release my thoughts freely. So far I've shared most every experiment I did, and say what it does or does not do for me. Or what I think/believe it does like in this case. So this experiment isn't any different, my excuses for the confusion. I see this as a sequel to my earlier cross talk cancelation experiments. No harm intended though. Out of sheer enthusiasm I can get carried away and post a lot. If I'm in such a "thought wave" I figure it's time to retreat to my own little corner on this forum and vent there. Make sense?
If there's any side effect of me posting this here that will result in more people checking out the phantom center thread, that's what I'm actually secretly hoping for. 😀
It looks like you've found your way back again 😉. See you there!
If there's any side effect of me posting this here that will result in more people checking out the phantom center thread, that's what I'm actually secretly hoping for. 😀
It looks like you've found your way back again 😉. See you there!
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I totally enjoy your thoughts on all of this. I often get a bit off subject too, but believe that can be productive sometimes as well.
Back to reality... the Phantom Shuffler, what is it and how does it work? That question intrigued me so I went on a crusade to figure it out. It all started with BYRTT posting some Dirac pulses summed with a slight time delay.
That triggered me to start investigating what it was that I liked about the shuffler. If you want to see what I tried, follow this link...
I'll try and explain what I think is happening... First we start with a picture of what cross talk is:
(picture "borrowed" from Steve Hoffman forums)
The thick red and blue lines are the direct sound. They will arrive at your ears first. The thin lines cannot be avoided though, sound from the left channel is going to reach the ear on the right side and vice versa. There will be a time difference between those two sounds. Depending on how the speakers are setup and even your head size plays a role.
If we listen to phantom information both our left and right channel are playing the same information. But we saw above that sound also travels around your head reaching the other ear. That's where the sound will interfere and will cause comb filtering to happen (oh no, not that again 😀).
So what does it look like, you may ask. If we stick with an average delay of 0.270 ms we can figure it out.
Sound travels from the left speaker to the left ear, the wave continues and reaches the right one 0.27 ms later. But that particular ear just received the same info as the left if the content was panned to the center. This is where the combing starts. If we assume a Dirac pulse, arriving at that right ear we would get the delayed content of the left ear interfering with that pulse 0.27 ms later.
On to REW, we take 2 Dirac pulses and delay one of them with 0.27 ms. This will give us a view of our comb pattern:
So we get a first wave front, free from combing and 0.27 ms later it starts combing (at both ears) and creates the above pattern at our ears.
It actually fitted my experience, I've told you guys I cut 2 frequencies in my mid/side processing. Guess what they are!
One cut is at 3700 Hz, Q = 2.5 and gain = -1.4 dB and the second one is at 7270 Hz, Q = 2.5 and gain = -1 dB. Those settings were a "left over" from my earlier cross talk cancelation experiments. I found it cleared up some center panned vocals that were harder to follow without the cuts. It's in this thread somewhere.
Good fit right? If you look at the summed Dirac comb filter pattern it makes perfect sense. I even cut a tiny bit in the sides signal to fine tune my balance. But it wouldn't/shouldn't be absolutely necessary.
Now why does the phase shuffle work? What does it do to the above situation?
To find out we start to sum the shuffler IR instead of that perfect Dirac pulse.
Again we offset one of the pulses by 0.27 ms and look at the comb filter result.
Red trace is the shuffler called "Rephase Shuffle-2.wav" from Pano's thread. Purple trace is the Dirac again to compare.
Do you see the difference? By alternating the phase, which is what the shuffler does (see a couple of posts above), we move the dips to a different location. We created a phase difference at ~2000 Hz between both channels of 60 degree (or slightly more).
The signal still sums, but the dip is moved in frequency by that subtle phase turn. Because the phase is opposite on the other channel the result at the other ear will look different.
Here's a view of both results. One trace would represent the left ear signal and the other one the right ear:
Now we see the magic! You either get that Dirac comb pattern at both ears (without shuffle) or we get the above combing, slightly different for each ear but together creating a better balance. Remember, we already heard the direct (non disturbed) wave front for 0.270 ms before this happens.
So the choice is to listen to the Dirac combing at left and right ear, screwing up our balance or use a shuffler to shift the dips and get a more even balance to process in our head.
Let's look at an average of the shuffler combing and the Dirac combing as we get to process it in our head:
See how most dips are filled in? This actually brightens the phantom center. Making it sound more real. The dips eat away less of the signal arriving at the ears. It even gave me more sense of depth. Earlier I quoted material that told us boosting at 2 KHz gives more sense of depth. Care to guess why that is if you look at this story? 🙄
Now why would it only work on the phantom center material? If you look at the sounds panned hard to the left, they don't have an equivalent sound wave comming from the right channel to interfere with the left channel sounds that's leaking to the right ear. And if we combine the left shuffle IR with a delayed left shuffle IR we end up with: the exact same shape as the Dirac comb pattern. So for panned sounds we get some cross talk, possibly coloring what we hear but not the combing, eating away at our wave front.
In other words: no change to the left or right panned sounds, only a perceptual change of the phantom center. Except for the possibility of hearing the small phase shifts we introduced to the signal chain. Some sounds will be a bit early (by about 0.16 ms max) or late (by the same amount). I'll have to admit, I couldn't hear that difference.
I was more in awe of what the shuffler did for the phantom center! 😱
I hope you guys like this theory, it's the best I can do right now 🙂.
Ronald
I've got to criticize myself in this rambling. The last bit about panned sounds to one speaker isn't accurate. I mention combining the two signals to form a Dirac shape while in fact this isn't happening. There is no interfering sound, so we get the first wave at one ear, and a delayed (and influenced by head shading) wave at the other, but no Dirac shaped wave, only the cross talk.
So the panned signals, panned somewhere between both speakers are the ones that suffer from the comb coloring the sound. Not the sides. At least not in my simple theory. The rest still stands for the time being. 😀
All the praise for the shuffler, this seems like something I'll have to try soon.
The original document says that such phase decorrelation should give more stability to the phantom centre and resist collapsing of the centre image to the nearest speaker for non-equidistant listening position from both speakers more compared to the conventional setup.
This possible sweet-spot widening interests me more than filling up the hole in the 2khz region, which is good too.
So, what is your off-axis listening experience so far with this shuffler in your system?
Is there any change in the centre image focus?
Nice simulations btw.
The original document says that such phase decorrelation should give more stability to the phantom centre and resist collapsing of the centre image to the nearest speaker for non-equidistant listening position from both speakers more compared to the conventional setup.
This possible sweet-spot widening interests me more than filling up the hole in the 2khz region, which is good too.
So, what is your off-axis listening experience so far with this shuffler in your system?
Is there any change in the centre image focus?
Nice simulations btw.
I did sense more stability in the phantom center. Though I had way too much fun in the center to focus on that. 🙂
I'm still playing around with various settings to see what does what. Filling that 2KHz dip is the biggest plus in my book. On the phantom center thread I shared a file only targeting that dip. Though in my preliminary tests filling in the dips above it surely helped too.
You can try playing with the tracks dynoMike shared. It's important that phase is well behaved and that requires an absence/avoidance of early reflections.
I'm still playing around with various settings to see what does what. Filling that 2KHz dip is the biggest plus in my book. On the phantom center thread I shared a file only targeting that dip. Though in my preliminary tests filling in the dips above it surely helped too.
You can try playing with the tracks dynoMike shared. It's important that phase is well behaved and that requires an absence/avoidance of early reflections.
I take a small break and look where all these thread are running away with so much info to catch up!
You all truly deserve a big pat on the back for pushing the boundaries of DIY Audio stuff!
I'll go back to reading and catching up!
You all truly deserve a big pat on the back for pushing the boundaries of DIY Audio stuff!
I'll go back to reading and catching up!
I wonder how this would go over if you included this shuffler in a self powered speaker as an optional setting? Perhaps you just don't say anything and put it into the dsp with the phase shift already installed?
It is tempting 🙂. But I'd definitely make it optional. What if a mixer/master engineer decides to put it in an album... plus it will likely have less of an effect (or an undesirable effect) with speakers placed near reflective surfaces.
So you think with a normally reflective room that most people would have you wouldn't notice an improvement in the phantom center image? Is this specifically working only in a room where first reflections have been absorbed or reduces with panels? It just seemed like the concept would work even in a normally reflective room to improve the center imaging without really affecting the side channels integrity.
I have no experience with it in a more reflective environment but I bet curing the 2 KHz dip would work.(*) On the Phantom Center thread dynomike tried it on his big home speakers with less than desired results though, he loved it on his more near field speaker setup. I guess more experimenting is needed, I hope more people try this out!
This isn't a line array thing after all. It's a flaw in the Stereo concept. So many more could potentially benefit from something like this.
(*) = the Toole measurement I included in some of my graphs was taken in a reflective room. But no telling how early those reflections were. If I had to gamble and say a ~3 ms gap (reflection free) would be needed to make this work. But it could be more.
This isn't a line array thing after all. It's a flaw in the Stereo concept. So many more could potentially benefit from something like this.
(*) = the Toole measurement I included in some of my graphs was taken in a reflective room. But no telling how early those reflections were. If I had to gamble and say a ~3 ms gap (reflection free) would be needed to make this work. But it could be more.
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That was what I was thinking in that this is really a stereo problem with comb filtering of at least a portion of the center phantom image. I guess I would have to play with it in different types of rooms and configurations to see if just correcting the 2K problem would be a good thing.
Fixing that gap only already brings a good improvement. I've played with the 1850 Hz fix only today and hope to add the 5500 Hz in for a next test. Higher than that probably isn't needed anyway due to head shading and the short wavelengths there. It can still bring a perceptual change but it would be extremely difficult to tell if it's because of dips and peaks at different places or a real improvement. The one at ~1850 Hz (based on an average sized head) is the one that will stand out.
Sounds like your on top of the problem and experimentation. As you say just fixing this at that simple 1.8Khz frequency range sounds promising for the typical room and normal stereo image.
I'm still playing and having fun with this shuffler and decided to try and swap channels of the shuffler, making the other one lead for a change. That actually shifted my stage a bit.
I figured it would be because of an imbalance of either frequency or phase. I've always known there were slight differences in phase, while the FR is damn near the same left and right. As I now have found an easy trick to combine FIR filters I figured to EQ my phase too. Really only fine-tuning it as DRC has done the hard work already.
Here's the original phase as measured:
(viewed with a frequency dependent window of 5 cycles)
And the RePhase EQ-ed phase:
Not a huge difference but probably a better base for this shuffler experiment. It made the impulses look quite identical as well.
It will still take me a while to get to the point where I can definitely say if the shuffler is positive in every way. So far I think it can be, but I need to get it to my liking (adjust the new tonal balance) and live with it for a while to be sure.
I might have to make changes to the ambient mix as well as I let that one run up to ~2 KHz in the center. I'll play with that cut-off just to see what that does. What I've heard and experienced so far seems promising enough to put more time into it. Though I have less time available nowadays.
I figured it would be because of an imbalance of either frequency or phase. I've always known there were slight differences in phase, while the FR is damn near the same left and right. As I now have found an easy trick to combine FIR filters I figured to EQ my phase too. Really only fine-tuning it as DRC has done the hard work already.
Here's the original phase as measured:
(viewed with a frequency dependent window of 5 cycles)
And the RePhase EQ-ed phase:
Not a huge difference but probably a better base for this shuffler experiment. It made the impulses look quite identical as well.
It will still take me a while to get to the point where I can definitely say if the shuffler is positive in every way. So far I think it can be, but I need to get it to my liking (adjust the new tonal balance) and live with it for a while to be sure.
I might have to make changes to the ambient mix as well as I let that one run up to ~2 KHz in the center. I'll play with that cut-off just to see what that does. What I've heard and experienced so far seems promising enough to put more time into it. Though I have less time available nowadays.
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Did you post about the way to easily combine FIR filters? Don't remember reading about it...
Ah... I wish my phase looked like that! I guess I have way too many reflections in my concrete room.
Right here: http://www.diyaudio.com/forums/full-range/242171-making-two-towers-25-driver-full-range-line-array-219.html#post4694469
I've been using it extensively ever since! 🙂 If you need the peak to be exactly at the same position, the hardest part is to edit out the silent, that I fist add to the beginning and end of the file. I suspect it only to be of importance if you run more IR's simultaneously though. Like I do with my ambient channels.
I've been using it extensively ever since! 🙂 If you need the peak to be exactly at the same position, the hardest part is to edit out the silent, that I fist add to the beginning and end of the file. I suspect it only to be of importance if you run more IR's simultaneously though. Like I do with my ambient channels.
Somehow , I missed that post.
Ok, but unfortunately, I'm back on a Mac now, and it doesn't have the "Disk writer" option.
Couldn't I use a DAW or something similar to sum up both .wav filter files?
Ok, but unfortunately, I'm back on a Mac now, and it doesn't have the "Disk writer" option.
Couldn't I use a DAW or something similar to sum up both .wav filter files?
Perceval,
Okay missing "Disk writer" option then remember somewhere over phantom image thread someone mentioned use Sox, other than that i could be wrong but think should be possible too with some investigation into Audacity where there is so many packages and plugins available and think especially if Taps/FFT length and also sample rate happen is same for the two IR-wav files to blend it should be possible.
wesayso,
Nice new left verse right results for phase, you have been in engine room to calibrate the two cylinder engine so ignition timing is in absolute sync now via "Phase EQ" tab, couldn't resist tweak your two carburetors vacuum throttle too just a little little bit on the next "Gain tab" shifting from default minimum-phase to linear-phase with small numbers in below graphs. With new dimension for system critical quality control have set new check mark : )
Okay missing "Disk writer" option then remember somewhere over phantom image thread someone mentioned use Sox, other than that i could be wrong but think should be possible too with some investigation into Audacity where there is so many packages and plugins available and think especially if Taps/FFT length and also sample rate happen is same for the two IR-wav files to blend it should be possible.
wesayso,
Nice new left verse right results for phase, you have been in engine room to calibrate the two cylinder engine so ignition timing is in absolute sync now via "Phase EQ" tab, couldn't resist tweak your two carburetors vacuum throttle too just a little little bit on the next "Gain tab" shifting from default minimum-phase to linear-phase with small numbers in below graphs. With new dimension for system critical quality control have set new check mark : )
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Another way to combine FIR filters is to run a sweep through multiple convolver instances, then deconvolve the resulting "processed sweep" against the original sweep tone.
Impulse response deconvolution tool software - Voxengo Deconvolver - Voxengo
I use the Voxengo Deconvolver all the time to create FIR filters out of anything you want.
Impulse response deconvolution tool software - Voxengo Deconvolver - Voxengo
I use the Voxengo Deconvolver all the time to create FIR filters out of anything you want.