"Freeverb" port...

Tom7777 · 9 May 2005

Thanks 🙂

Shifrin · 9 May 2005

Actually, I wrapped it into a VST effect with the little knobs on to control it and tested it out in my sequencer with various synths/drums/samples etc and it's surprisingly good! Any bugs or anything let me know and I'll update it (or if I find any myself etc).

It's very simple to add a pre-delay to it too - but that wasn't in Freeverb so I left it out 😉

Shif.

unkargherth · 9 May 2005

Very Nice work !!!

I think there's suficiently good to work as a Synth effect.

On the predelay issue, is easy to add it externally, so better don't include in the reverb itself

Shifrin · 9 May 2005

unkargherth wrote: Very Nice work !!!

I think there's suficiently good to work as a Synth effect.

Yep, it's not bad at all is it. Thanks to NAS for poiting me in the direction of the original Jezar sources, and to Jezar for making them public domain 🙂

unkargherth wrote: On the predelay issue, is easy to add it externally, so better don't include in the reverb itself

My thoughts exactly 🙂

Shif.

Nu Audio Science · 9 May 2005

Woohoo LATKs Freeverb Creakbox - Its gone mad round here and i love it 😉

Really nice work here by the way Shif, Stuff like this really is making me see how infinitely powerful SM is compared to anything else.

Kitchen Sink · 11 May 2005

Shifrin wrote: Ok, here is an attempt at converting the 'Jezar' Freeverb code to SM.

Totally completely awesome!! 😮 😀 Amazing.

skOre · 11 May 2005

Love your design style shif... the rectangle connections 🙂

Shifrin · 11 May 2005

skOre wrote: Love your design style shif... the rectangle connections 🙂

Hehe, it's great that we have these lovely 'bendy' connections in SM but sometimes it's more clear (to me) to add a dummy module for the purpose of making a wire bend at a right angle 😉

Oh yeah :-

I checked the entire schematic against the Freeverb source and they are now (to my knowledge) algorithmically identical, with one expection: My allpass filter is a standard feedforward+feedback comb design. The one in the source is 'weird' and when I implemented it I got a more harsh metallic sound. So I left my allpass filter as is. Everything else is the same as the source though!

Only thing left to do might be to add some denormal checking in the feedback paths of the filters.

Shif.

Nu Audio Science · 12 May 2005

Can you believe it, The actual Freeverb source is hosted at KVR DOH

malc · 12 May 2005

This is great Shif!

You might be interested to know that you can create links with right-angle bends without the need for a 'corner' module. Go to Options | Advanced and set the link curvature to zero (straight). This allows you to do this:

It's not perfect though. For a start it's an application setting and so if you send it to someone else it might look different. Also, the interaction for the control points doesn't provide any mechanism for getting at links that are below the link that is on top.

That all said, if you want to get this effect you may still find it useful. I'm sure that this is something we will enhance later down the line.

Malc.

Tom7777 · 12 May 2005

I think Freeverb has a really nice sound to it 🙂

Shifrin · 12 May 2005

Thats interesting to know malc, cheers!

Shif.

Shifrin · 12 May 2005

Nu Audio Science wrote: Can you believe it, The actual Freeverb source is hosted at KVR DOH

Oh just saw you posted that, any chance you could give the link? I tried searching KVR for it myself but came up with nothing but hits for archived forum messages. I'd be interested to compare the source with that which you posted a link to 🙂

Shif.

Nu Audio Science · 12 May 2005

http://www.kvr-vst.com/resources/pluginsrc/freeverb_src.zip

Hahahahahahahahah See you cant always trust searches 😉

Shifrin · 12 May 2005

Nu Audio Science wrote: http://www.kvr-vst.com/resources/pluginsrc/freeverb_src.zip

Hahahahahahahahah See you cant always trust searches 😉

Thanking you! Will compare it to what I already have, just for any inconsistencies 🙂

Shif.

ik_ik_ik · 11 Jun 2005

Shifrin wrote: Only thing left to do might be to add some denormal checking in the feedback paths of the filters.

Shif,

I had a look at your Freeverb port today. It's really interesting and educational to see the guts of something like that 🙂 Amazing layout as always too!

Something came up whilst I was trying it out...

Fire a click into the reverb, sounds great 🙂 Then, leave it and the CPU hits the roof after about 30 seconds (on my Centrino 1.6GHz at full throttle). If I fire some more clicks into the reverb then things seem to recover. Seems to be repeatable and doesn't seem to depend too much on the reverb parameters so I'm wondering if this might this be related to the denormal checking you mentioned?

Cheers,

Inigo

Shifrin · 11 Jun 2005

Actually I think I had a similar thing happen with the CPU jumping and forgot to mention it here!!!

I don't think there should be denormal problems as the schematic gets compiled to SSE code?!

Maybe jorge could offer some info/advice!

Shif.

jorge · 11 Jun 2005

Shifrin wrote: Actually I think I had a similar thing happen with the CPU jumping and forgot to mention it here!!!

I don't think there should be denormal problems as the schematic gets compiled to SSE code?!

Maybe jorge could offer some info/advice!

Shif.

Denormals are not related to SSE but to the CPU. I think P4 and Celeron have a problem with denormals while Pentium M doesnt. I´m not sure about Athlon but I think it is a lot better than P4 and Celeron.

The problem described above sounds like a tipical Denormal problem as the values recirculating around a feedback path keep getting smaller until they´re treated as denormals which I´m guessing is after the 30 sec.

Getting rid of denormals is something that should be done in the schematic itself. One way is to add and subtract 1e-18 in the feedback path.

ik_ik_ik · 12 Jun 2005

jorge wrote: Denormals are not related to SSE but to the CPU. I think P4 and Celeron have a problem with denormals while Pentium M doesnt. I´m not sure about Athlon but I think it is a lot better than P4 and Celeron.

The problem described above sounds like a tipical Denormal problem as the values recirculating around a feedback path keep getting smaller until they´re treated as denormals which I´m guessing is after the 30 sec.

Getting rid of denormals is something that should be done in the schematic itself. One way is to add and subtract 1e-18 in the feedback path.

If I remember right Jorge (from the good old runaway CPU topic) we both use Pentium-M (Centrino) machines - maybe they do have problems still (there's the usual sea of anecdote on the web)?

This was an interesting article I ended up reading after the 1e-18 suggestion. I tried the add subtract trick in the feedback paths in both the "comb" and "allpass" sections but SM went into a spate of crashing out :-( Probably my error as I'm tired; I'll have another look tomorrow...

Inigo

Shifrin · 12 Jun 2005

I'll have a look at the denormal issue, funny thing is I run an Athlon XP and have had no problems with denormals before, even with VST/i's that are known to give bad denormals on P4 processors.

Shif.

ik_ik_ik · 13 Jun 2005

I've fiddled about with the comb modules but no luck so far. I'm pretty sure the problem is there rather than the allpass filter chains since isolating the combs gets rid of the problem.

I noticed yesterday that the problem seems worse when very short impulses are fired in to the reverb, less so with longer sounds. It could be a property if not weakness of the actual algorithm.

Jorge, SM crashed out when connecting an empty float to the damping input of the Freeverb module (whilst it was running). I'll email you the dmp.

Inigo

jorge · 13 Jun 2005

ik_ik_ik wrote: Jorge, SM crashed out when connecting an empty float to the damping input of the Freeverb module (whilst it was running). I'll email you the dmp.

Thanks Inigo. Much more useful than the dmp is the schematic itself so we can recreate it. I'm assuming it´s the one posted on this thread.

ik_ik_ik · 13 Jun 2005

jorge wrote: ik_ik_ik wrote: Jorge, SM crashed out when connecting an empty float to the damping input of the Freeverb module (whilst it was running). I'll email you the dmp.

Thanks Inigo. Much more useful than the dmp is the schematic itself so we can recreate it. I'm assuming it´s the one posted on this thread.

Yep. That's the one (as found in sk0re's NO_Effects pack).

Shifrin · 13 Jun 2005

ik_ik_ik wrote: I've fiddled about with the comb modules but no luck so far. I'm pretty sure the problem is there rather than the allpass filter chains since isolating the combs gets rid of the problem.

I've not had much free time to look at this recently, but there must be a way to fix it 🙂 I'll have a look at the comb sections too, assuming I don't get crashes all the time 😉

Shif.

oddson · 21 Sept 2005

Anyone interested in this project might want to have a look at this bug report.

ik_ik_ik wrote: I've fiddled about with the comb modules but no luck so far. I'm pretty sure the problem is there rather than the allpass filter chains since isolating the combs gets rid of the problem.

Both the combs and allpass have mono feeds adding at the input of a delay - which appears to be problematic.

oddson · 22 Sept 2005

This is primarily for sambean... but if anyone else knows please feel free...

I'm looking at your impulse graph in the bug thread, I'm not sure why the "correct" impulse chart is the one you've indicated, other than it matches what the literature says is correct.

It seems to me the time-zero spike should be negative as the only path that doesn't go through the delay is being multiplied by the inverse gain param (through the so called feed forward path).

Any chance of my second free DSP lesson? 😉

Oh yeah, the freeverb port sounds better (i.e. less 'metalic') with the explicit add components. (But I haven't done any systematic check against alternatives.)

Also: If Jorge's diagnosis about the stage addition is correct then shouldn't the explicit add version be correct. 😕

And: What does it mean that poles show negative and positive at what appears to be the same time on the 'incorrect' impulse charts.

And: Can you shed any light on the crazy FFT charts in my post?

Ever greedy for answers! 😇

skOre · 22 Sept 2005

Sometimes, the correct things sound worse than broken stuff...

sambean · 22 Sept 2005

I'll try to explain what I can as best I can.. 😕 .. But if anyone else can put their 2p worth in please do..

I modified the layout slightly from how Shif had designed it to match the diagram I showed of the allpass filters where the the feedback input is equal to g ..

In this layout the feedback path is multiplied by the inverse (-g), and the feedforward by (g), thats why the first spike is positive.. (1 * g)

We have to wait for this impulse to pass through the delay , it then comes out the delay (delay out = DOut = 1), through the feedback loop (DOut * -g), and through the feedforward loop again (DOut * -g * g)

At this point we have:

Output = delay out + feedforward loop = Dout + Dout * -g * g = Dout (1 - g^2)

New Delay input = DOut * -g (from feedback loop)

as the new delay input = delay output * -g this implies the next spike will be negative and each consecutive spike will alternate between positive and nagative.. And also as g < 1 and (1-g^2) <1 each consecutive spike will be smaller in amplitude.

So for the impulse response we have

g, (1- g^2), -g(1- g^2), g^2(1 - g^2)...

for g = 0.7

0.7, 0.51, -0.357, 0.2499,... which is what we see for the impulse response..

sambean · 22 Sept 2005

Just found this.. Which shows you can have the inverse g on the feedforward and the positive g on the feedback..

http://www.harmony-central.com/Effects/ ... lpass.html

For the 'incorrect' resposes seen in the other thread (positive and negative spikes at the same time) what I think is happening is the output is being calculated from the delay output and the feedforward loop then the feedback loop is is being calculated. so on the following sample we have the impulse being spread over 2 samples, one positive one negative..

As to why the allpass (should) have a flat response consider the feedback and feedforward sections separately (set the value for the other =0)- the feedback section's frequency response is that of an upward comb filter and the feedforward section has a downward comb filter, add them together and they cancel each other out, leaving a flat frequency response..

What you were seeing in your frequency response of the files you posted was some kind of strange comb filter (hence metallic sound?).. Have a look at the frequency response with the other FFT (non-logarithmic)

oddson · 22 Sept 2005

Yah - that's the page I was going by...

It's going to take me a little time to digest all this Sam but thanks so much for taking the time! 😀

ake · 24 Sept 2005

The origins of this algoritm I think is here

http://www.jamminpower.com/PDF/reverberation%20business.pdf

Just some history

åke