<div dir="ltr">Yeah, my [filterplot.mmb] abstraction actually wraps the phase to -pi to pi and scales that to -1 to 1. I don't remember why I did the scaling. ;-) Also, I don't know if it matters with how you're analyzing [phaseshift~], but the frequency axis is non-linear. You can change it by sending a [linfreq 1( message (I think I forgot to put that in the helpfile).<div>
<br></div><div>You're right that a second-order filter doesn't necessarily mean it is a biquad structure, but as long as it is a linear filter, you can recreate any second-order filter using a biquad. You just put in 0 for the coefficients you aren't using. However, second-order all-pass filters are likely going to be biquads, since the feedforward and feedback coefficients will be inverses of each other (i.e. b0 = a2, b1 = a1, b2 = a0).</div>
<div><br></div><div>Anyway, I don't have access to Max these, so I can't really look at it. There is this filter described here (<a href="https://ccrma.stanford.edu/~jos/pasp/Phasing_2nd_Order_Allpass_Filters.html" target="_blank">https://ccrma.stanford.edu/~jos/pasp/Phasing_2nd_Order_Allpass_Filters.html</a>) that gives a response similar to what you described with f = 4kHz and R = .1, but I don't think that's the one given what it says in the [phaseshift~] reference page. The paper describe this filter says R should be exp(-pi * bandwidth / samplerate), and that usually results in .5 < R < 1.</div>
<div><br></div><div>Hope that helps at all.</div><div>.mmb</div>
</div><div class="gmail_extra"><br><br><div class="gmail_quote">On Sat, Oct 5, 2013 at 7:14 PM, Alexandre Torres Porres <span dir="ltr"><<a href="mailto:porres@gmail.com" target="_blank">porres@gmail.com</a>></span> wrote:<br>
<blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div dir="ltr"><div>hi mmb, thanks for showing up :)</div><div><br></div>hmmmm, my problem was that the phase response graph generated from your Pd patch based on RBJ looks different than the one from max's phaseshift. But it just occurred to me that one thing about it might only be a matter of normalizing it and displaying in the same way.<div>
<br></div><div>For example, your patch gives us a drop from 0 to -1 and then from 1 to 0, while phaseshift in Max is from 0 to -2pi continuously. I'm now considering that both behaviours could be related, only that your patch "wraps" it around -1 back to 1. What do you think?</div>
<div><br></div><div>But even so, there's also the issue of getting the Q parameter to behave in the same way. Max's phaseshift, when set to Q = 0.1 and freq = 4KHz will give you a linear drop from 0 to -2pi. Now, I can't seem to get that based on RBJ's cookbook formulas and your patch. But then, another thing I haven't thought of might be a difference in the scale plot...</div>
<div><br></div><div>One way or another, the Q parameter seems off. </div><div><br></div><div>So, as you can see, there are these plotting differences, but I know what you mean, that is what I was suspecting too, it sure looks like the same thing at a first glance, meaning you can get to it from a biquad coefficient perspective. The problem is that max's phaseshift isn't very clear about what it really is, other than saying it is a second order filter. But that doesn't have to imply it is the same as a second order biquad, does it?</div>
<div><br></div><div>Thanks</div></div><div class="HOEnZb"><div class="h5"><div class="gmail_extra"><br><br><div class="gmail_quote">2013/10/5 Mike Moser-Booth <span dir="ltr"><<a href="mailto:mmoserbooth@gmail.com" target="_blank">mmoserbooth@gmail.com</a>></span><br>
<blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div dir="ltr">From looking at the helpfile for [phaseshift~], this sounds very much like the all-pass filter from Robert Bristow-Johnson's EQ Cookbook. You can calculate the biquad coefficients for it like this:<div>
<br>
</div><div>w0 = 2*pi*frequency_in_Hz / sample_rate</div><div>alpha = sin(w0)*sinh(ln(2)/2*Q*w0/sin(w0))</div><div><br></div><div>fb1 = 2*cos(w0) / (1+alpha)</div><div>fb2 = (-1+alpha) / (1+alpha)</div><div>ff1 = -fb2</div>
<div>ff2 = -fb1</div><div>ff3 = 1</div><span><font color="#888888"><div><br></div><div>.mmb</div></font></span></div><div><div><div class="gmail_extra"><br><br><div class="gmail_quote">
On Sat, Oct 5, 2013 at 12:31 PM, Alexandre Torres Porres <span dir="ltr"><<a href="mailto:porres@gmail.com" target="_blank">porres@gmail.com</a>></span> wrote:<br>
<blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div dir="ltr"><div>> the phase response given in phaseshift's help file suggest otherwise.<br><div class="gmail_extra">
<br></div></div><div class="gmail_extra">it's more like the response from miller's H14 example...</div>
<div class="gmail_extra"><br></div><div class="gmail_extra">So I guess you can have a 2nd order one (lie phaseshift) by putting two of these together, right? And I suspect it doesn't really need to have anything to do biquad just for being "2nd order", huh?</div>
<div class="gmail_extra"><br></div><div class="gmail_extra">cheers</div><div><div><div class="gmail_extra"><br><br><div class="gmail_quote">2013/10/5 Alexandre Torres Porres <span dir="ltr"><<a href="mailto:porres@gmail.com" target="_blank">porres@gmail.com</a>></span><br>
<blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left-width:1px;border-left-color:rgb(204,204,204);border-left-style:solid;padding-left:1ex"><div dir="ltr">Anyway, next on my list is finding out how to implement max's [phaseshift~], which is also an allpass filter. There's no Pd clone for it so it seems, right? <div>
<br></div><div>Well, it doesn't really what it is other than a 2nd order filter. From that I could think you can generate it with [biquad~], but the phase response given in phaseshift's help file suggest otherwise.<br>
<div class="gmail_extra"><br></div><div class="gmail_extra">any contributions welcome</div><div class="gmail_extra"><br></div><div class="gmail_extra">thanks a lot<br><br><div class="gmail_quote">2013/10/5 Alexandre Torres Porres <span dir="ltr"><<a href="mailto:porres@gmail.com" target="_blank">porres@gmail.com</a>></span><br>
<blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left-width:1px;border-left-color:rgb(204,204,204);border-left-style:solid;padding-left:1ex"><div dir="ltr">but this way it won't be the same as cyclone's [allpass~], the way I did it is equivalent to it (and max's).<div>
<br></div><div>cheers</div></div><div><div><div class="gmail_extra"><br><br><div class="gmail_quote">
2013/10/3 Chris Clepper <span dir="ltr"><<a href="mailto:cgclepper@gmail.com" target="_blank">cgclepper@gmail.com</a>></span><br><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left-width:1px;border-left-color:rgb(204,204,204);border-left-style:solid;padding-left:1ex">
<div dir="ltr">You only need one delay line for the allpass.<div><br></div><div>feedforward = input * -gain</div><div>feedback = delayout * gain</div><div>delayin = input + feedback</div><div>output = delayout + feedforward</div>
<div><br></div><div><a href="http://www.spinsemi.com/knowledge_base/effects.html#Reverberation" target="_blank">http://www.spinsemi.com/knowledge_base/effects.html#Reverberation</a><br></div>
</div><div><div><div class="gmail_extra"><br><br><div class="gmail_quote">On Thu, Oct 3, 2013 at 11:29 AM, Alexandre Torres Porres <span dir="ltr"><<a href="mailto:porres@gmail.com" target="_blank">porres@gmail.com</a>></span> wrote:<br>
<blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left-width:1px;border-left-color:rgb(204,204,204);border-left-style:solid;padding-left:1ex"><div dir="ltr">i hope i guess i figured it out on how to implement it with delay lines. see attachment. And I realize you can't do this with [fexpr~] or [biquad~] because the sample delay length is kinda big for that, right?<div>
<br></div><div>cheers</div></div><div><div><div class="gmail_extra"><br><br><div class="gmail_quote">2013/10/3 Alexandre Torres Porres <span dir="ltr"><<a href="mailto:porres@gmail.com" target="_blank">porres@gmail.com</a>></span><br>
<blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left-width:1px;border-left-color:rgb(204,204,204);border-left-style:solid;padding-left:1ex"><div dir="ltr">cool, but do you know how to implement cyclone's [allpass~] with it? <div>
<br></div><div>It's really unclear to me what is the relation of this pass filter with the one you can generate with biquad coefficients, or with raw poles/zeros objects for that matter.</div>
<div><br></div><div>Well, one way or another, it's also unclear to me how to do it with delay lines.<br></div><div><br></div><div>seems that it is related to a comb filter, right?</div><div><br></div><div>cheers</div>
</div><div><div><div class="gmail_extra"><br><br><div class="gmail_quote">2013/10/2 Chris Clepper <span dir="ltr"><<a href="mailto:cgclepper@gmail.com" target="_blank">cgclepper@gmail.com</a>></span><br>
<blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left-width:1px;border-left-color:rgb(204,204,204);border-left-style:solid;padding-left:1ex">
<div dir="ltr">Allpass for reverb is easy to do with delwrite~ and vd~. I used 32 of them today to recreate a famous 'deep space' reverb.</div><div class="gmail_extra"><br><br><div class="gmail_quote"><div><div>
On Wed, Oct 2, 2013 at 1:53 AM, Alexandre Torres Porres <span dir="ltr"><<a href="mailto:porres@gmail.com" target="_blank">porres@gmail.com</a>></span> wrote:<br>
</div></div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left-width:1px;border-left-color:rgb(204,204,204);border-left-style:solid;padding-left:1ex"><div><div><div dir="ltr">hi there, i see the biquad's coefficients can be set as an allpass filter, generated by frequency and "Q" parameters. But can it do the same as cyclone's [allpass~] filer? If yes, them how since the parameters for [allpass~] are different (delaytime and such).<div>
<br></div><div>One way or another, I guess that my real question is: how to implement [allpass~] from vanilla objects?</div><div><br></div><div>thanks</div></div>
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