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Re: Linear Phase Subwoofer

Reply #51
Hi, Wow, a Linear Phase cross over!! I'm new to Foobar2000 and I've only just installed and opened the app, but this is my first impression: Mindblowing!

What I noticed that I found mindblowing:

* The amazing flexibility and ability to control settings
* Ms delay resolution down to 0.1 ms. Just wow!
* Negative delay - so that sub may be "prelayed"
* 12 different types of cross over filters and with adjustability within each!! Wow!
* Adjustable FIR length in fractions of ms
* Snap back to original settings when unsync/resync - nice safety net when/if I mess things up

Features I found that possibly could be added are:
* Additional names for the filters such as their db/octave or "Linkwitz-Riley" etc
* A dual ms/distance scale for the delay
* A version of delay adjust for when multiple subs are used and they are not equidistant to the main speakers/listener.
* In addition, I understand this is mono signal for the sub channel, could it be made into stereo?

I have a few questions:

If I unsync L/R there will be some influence on the total cross over frequency/timing curve. I guess this influences phase? Will this enable stereo LFE if I have more subs? I have two, and cross them over quite high in the range, so I will need stereo or lower the cross over frequency.

Bass processing is resource intensive. The adjustable FIR lengths, which I assume is the same as "filter taps" (please correct me if I misunderstand) enables a balance between resource usage, the time it takes to process and quality. If I set it to max, the 700 ms, I assume this will render the highest resolution in the bass. Is this correct?

Thank you for this outstanding plug in!!


Re: Linear Phase Subwoofer

Reply #52
Ignore that stereo question. I guess unsyncing L/R could enable off-axis listening?

Re: Linear Phase Subwoofer

Reply #53
Thank you for this outstanding plug in!!
Hi, thanks for reply - you make me very happy!

Additional names for the filters such as their db/octave or "Linkwitz-Riley" etc
"Linkwitz-Riley" identical to "Classic" filter. I named it to "classic", because it draws by another formula at logarithmic scale and parametrized by another concept. I don`t like db/octave regulator, because it reflect physical realization with discrete steps.

A dual ms/distance scale for the delay
Yes, i think about this.

* A version of delay adjust for when multiple subs are used and they are not equidistant to the main speakers/listener.
* In addition, I understand this is mono signal for the sub channel, could it be made into stereo?
In first versions i made a support of second sub with independent delay and volume, but remove it later. Two reasons: it make using of plugin harder and no one use it. I plan to make independent plugin for this at future, if anybody need it. You can use Matrix Mixer (or some another) yet.

If I unsync L/R there will be some influence on the total cross over frequency/timing curve. I guess this influences phase?

Unsync mode is just simple equalization, no other side-effects.

The adjustable FIR lengths, which I assume is the same as "filter taps" (please correct me if I misunderstand) enables a balance between resource usage, the time it takes to process and quality. If I set it to max, the 700 ms, I assume this will render the highest resolution in the bass. Is this correct?

No, more taps no make higher resolution, it needs only for "brickwall" filtering and some peoples who like big taps. 700 ms = 32768 taps at 44.1 kHz samplerate. For example, the impulse response of "Soft" filter at 100Hz with width=2:




Re: Linear Phase Subwoofer

Reply #54
Thank you kindly for the explanatory and rapid reply E. Sokol!

Quote
In first versions i made a support of second sub with independent delay and volume, but remove it later. Two reasons: it make using of plugin harder and no one use it. I plan to make independent plugin for this at future, if anybody need it. You can use Matrix Mixer (or some another) yet.

Yes, please do. Bring it back!! I need it!! I use my dual "subs" up to ca 300 Hz and they will need individual alignment with the main speakers. There are other benefits of dual subs, for example when used with room correction software, they can be used to lift the dips in the response, that occur (not the way I have set them up, just to highlight other benefits of multiple subs).

I take the opportunity to return to the stereo question. Since this is built on LFE concept, doest that mean that stereo cannot be created in the dual sub independent plugin?

Thank you also for the Matrix Mixer link. I'll check it out.

I will be eagerly waiting for the dual sub independent plugin!!

Thank you again!

Re: Linear Phase Subwoofer

Reply #55
I have to add, the interface is SO easy to use. Just switching between the curves, setting the frequency, and sliding width it's really, really nice. And fast. A lot of fun to use!

Re: Linear Phase Subwoofer

Reply #56
I take the opportunity to return to the stereo question. Since this is built on LFE concept, doest that mean that stereo cannot be created in the dual sub independent plugin?
You mean independent LFE for left and right channels?

Re: Linear Phase Subwoofer

Reply #57
Yes, that's what I mean.

BTW, I've never seen so many types of crossovers applied to audio anywhere. I'm looking them up, to find out what their backgrounds are. I'm curious about what made you create this great application, and what your background is. A mathematician?

Re: Linear Phase Subwoofer

Reply #58
Yes, that's what I mean.
OK, i think about this.

BTW, I've never seen so many types of crossovers applied to audio anywhere. I'm looking them up, to find out what their backgrounds are. I'm curious about what made you create this great application, and what your background is. A mathematician?
No, i`m not mathematician. Say more: i have not subwoofer even:) Programming, graphics, DSP and mathematics is my hobbies. I have some crazy ideas of non-standard audio processing, and this filters - one of them. My other interests - multichannel stereo splitting using fft, triple and quadro (ancient versions).

Re: Linear Phase Subwoofer

Reply #59
Cool! What, no sub! :-D I really like your creative approach! Graphics - your structure and layout of the subwoofer crossover is great. Really easy to use, great clarity and structure.

 DSP applied to audio is fantastic. I got into it for room correction, almost 20 years ago. Other ways of playing with audio is Ambiophonics, which you may have heard of, multichannel spherical Ambisonics, and binaural Bacch 3D.

Thank you for the triple and quadro links!

Re: Linear Phase Subwoofer

Reply #60
I'm trying to link your crossovers with known names. The classical is a modified Linkwitz-Riley if I remember correctly. I found a few pages of Douglas Self's book on active crossovers online. He names a lot of crossovers by their creators (perhaps you'll be in the next edition). Of your crossovers would you know if any of them correspond with any of the following names (and if so, which):

Le Cleac'h
Kreskovsky
Duelund
Butterworth
Bessel
Harsch

In the book he also discusses the types of crossover filters.

The first distinction Self makes is all pole vs non-pole, where an all poles have montonic roll-offs, meaning that once the response starts going down, it continues down. Non poles may come back up again, as in notch filters. Your filters are all pole.

The next distinction is symmetric  vs asymmetric as in having identical vs non identical slopes of both sides of the crossover. All of your filters are symmetric, showing identical slopes on both sides.

The next distinction Self makes is between all pass vs constant power vs constant voltage filters. All pass is a filter that sums the filter outputs in front of the loudspeaker to create a flat frequency response, aka amplitude, or SPL, or voltage response, on axis. All pass refers to the phase response with the phase of a first order all pass filter changing 180 degrees over the audio band, whereas a second order all pass filter phase changing 360 degrees across the audio band. The constant power crossover output filter sums the filter "...in front of the loudspeaker to create a flat frequency response in terms of power rather than in terms of SPL", that is it sums the total radiated power of both on-axis and off-axis response. This doesn't give a flat on-axis frequency response. The constant voltage crossover filter subtracts the output filter from the input, and when summing dual outputs a reconstructed linear phase waveform response is produced. The constant voltage filter shows a 6dB/octave output, regardless of the filter slope. I believe this is what your filters produce.

Self also discusses first-order crossovers stating that it is the only type that can accomplish linear phase, minimum phase and flat frequency response, hence it is the only type that allows a waveform to be accurately reconstructed when summing a high frequency and low frequency signal paths.  The shallowness of the first-order crossover slope of 6dB/octave requires that the loudspeaker drive elements can handle at least 2-3 octaves above and below the cross over frequency.




Re: Linear Phase Subwoofer

Reply #61
I'm trying to link your crossovers with known names.
I want to believe that my filters are unique - because all formulas was created by me. They designed as piecewise-defined function (except classic, erf, exponential and gudermannian) at logarithmic scale and named from a used functions names, which connect flat passband and stopband (and symmetric by design). They have not and can`t be have a physical prototypes.

The classical is a modified Linkwitz-Riley if I remember correctly.
Not quite.
Linkwitz–Riley filter can be parametrized only by integer step of roll-off values (12/24/48/etc dB/octave). Classic filter parametrized by required amplitude at cutoff frequency (-40 dB hard coded to have close view to other filters), but intersects with Linkwitz–Riley at some values. For example,
12 db/oct -> width = 6.62936
24 db/oct -> width = 3.31468
48 db/oct -> width = 2.20979

Re: Linear Phase Subwoofer

Reply #62
Ok, thank you! What about this: it looks like all the crossovers, regardless of the filter slope, do cross over at -6dB in your application. Is that the equivalent of this ""The constant voltage filter shows a 6dB/octave output, regardless of the filter slope."?

 
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