Impulse Response

[KG_is_back]

Hello guys, sorry for being here rarely lately - I'm in the middle of exam period, so not much time for Flowstone, sadly.

The reverb works suberB. The CPU usage is also not crazy high. Yes, the memins are currently implemented very badly in ASM module. 3.0.9 will surely provide considerable improvement in this area, namely the memrefin input. I also have several ideas how to improve loading of impulses even in current version. Instead of doing the stuff in green via greenFFT and then appending arrays, I think the better solution would be to create mem and then fill it with data using streams connected to analyser prim. I've done it that way in my project and it worked much faster. Hopefully I'll find time doing that soon.
Also there is an easy way to adapt the CPU usage to impulse length - just add a selector after each sub-convolver which would turn it off if impulse isn't long enough. Similarly the Impulse FFT preprocessing can be limited to only the needed parts via trigger blocker.
As for the longest IR, I recommend 20-30seconds maximum. With above-described smart-bypass mechanisms it wouldn't even affect CPU usage nor loading times (except schematic loading time). Also consider that many users use higher sample-rates!!! so 5seconds @44kHz would only correspond to 2.5seconds @ 96kHz.


@Spogg
Convolution (reverb) works by multiplying spectra (in frequency domain): Dry x IR = Wet
Similarly, if you have a dry signal and recorded wet signal you can calculate the IR by dividing the spectra: Wet / Dry = IR, which is called deconvolution.
Both are done in frequency domain, so you need a dry signal, which contains all frequency elements. Otherwise you get division by zero during deconvolution. Sine sweep is the best choice, since it is guaranteed to contain all frequencies.
It is possible to download free deconvolver online, as well as sine sweep. Or you may generate your own. Deconvolving them should be a matter of loading the wet file and dry file and clicking "start" and "save result" - it's not a rocket science.
Mathematically speaking Impulse response is a reverberation the room/device has when it is excited by an impulse (single sample click). Naturally, you can generate similar click via. hand clap, starting pistol or blowing up a baloon. However, the IR will have the frequency footprint of the used "device" imprinted on it. The same is true when using a speaker and deconvolution, but modern speakers have much flatter frequency response than any of above-mentioned. In the end of the day, the IR you end up with is actually a convolution of 4 IR's really - speaker IR x room IR x microphone IR x soundcard IR. That is normal and there is no way to avoid it.


As for the Flowstone reverb, perhaps we can simply add a stereo-shaper tool in front and after the convolver. By stereo shaper, I mean something that does: Lout=L*a+R*b; Rout=L*c+R*d;
By calculating the paropriate a,b,c and d you can widen/narrow the stereo field, rotate it, switch between LR and MS configurations, etc. It's more of a matter of making the GUI intuitive. Perhaps when I'll have more time messing with it...

[Spogg]

OMG what sheer fun this old Vulcan had this morning!
Sorry, I meant I had a fascinating investigation.

If anyone saw me clapping slowly in the street with a small device getting my attention, they will, at the very least, be rather puzzled. I've heard no sirens so I think I got away with it

Anyways. I recorded 3 areas, as per the filenames in the zip. In the unprocessed format the stairwell came out the most authentic I think. These first ones were only cut out and normalised to peak value.

I was a bit dissapointed with the street one so I did some editing, as per their filenames, and got wonderful results considering I haven't a clue what I'm doing.

I used a Tascam DR-07 portable recorder using the built-in microphones with windshield for the street one.
The impulse was a single clap about 1 metre from the recorder.
The files are 44k 16 bit stereo.
I auditoned using headphones which was good for assessing the detail.

@tulamide: I read and enjoyed the links you posted. I was expecting heavy-duty maths but they were very accessible for me. I still can't really claim to understand the magic but it doesn't matter because I don't need to. That's for the wizards here!

@Martin: I used your schematic many times auditioning these and it never glitched once. The files loaded quickly and worked perfectly. I guess there may be problems on lower spec systems maybe...

Here are the files I made.

Cheers

Spogg

[KG_is_back]

I wonder if Jean Baptiste Joseph Fourier was aware of what he found out when he came up with his Fourier analysis? I quote wikipedia, because I even don't understand that simple sentence: "Fourier's observation that some discontinuous functions are the sum of infinite series was a breakthrough."

No he probably wasn't. Fourier analysis was actually used a few times even before Fourier - namely in astronomy (gravitational effect of passing-by object on orbit of an asteroid). However, Fourier could not have anticipated that it will have such a widespread use, especially in fields like Quantum mechanics (microprocessors, chemistry, medicine (NMRI machines)) and statistics...

[tulamide]

From a german newspaper (I try to translate it as accurate as possible):

Birmingham, 19 January
Police reported an incident of typical english eccentricity. According to eyewitness accounts, a man with pointed ears who almost looked like he came from (here it is not easy to tranlate, because the german word "Vulkan" means either a volcano or vulcan, but since they mentioned pointed ears I guess "Vulcan" is the correct translation) Vulcan, sneaked through the streets of Birmingham while performing a strange ritual. Every few steps he stopped, formed the letter "V" with each hand and then clapped.

Several kids were traumatized, they just repeated "It was Spock's cousin, I swear. So it was all real" over and over again. Most women were able to flee or hide, hoping to not get kidnapped in space, but some were really attracted by his eyebrows, especially when he raised the left one, mumbling something like "Fascinating". The men just pretended they hadn't noticed anything.

[Spogg]

From a german newspaper (I try to translate it as accurate as possible):

Birmingham, 19 January
Police reported an incident of typical english eccentricity. According to eyewitness accounts, a man with pointed ears who almost looked like he came from (here it is not easy to tranlate, because the german word "Vulkan" means either a volcano or vulcan, but since they mentioned pointed ears I guess "Vulcan" is the correct translation) Vulcan, sneaked through the streets of Birmingham while performing a strange ritual. Every few steps he stopped, formed the letter "V" with each hand and then clapped.

Several kids were traumatized, they just repeated "It was Spock's cousin, I swear. So it was all real" over and over again. Most women were able to flee or hide, hoping to not get kidnapped in space, but some were really attracted by his eyebrows, especially when he raised the left one, mumbling something like "Fascinating". The men just pretended they hadn't noticed anything.

Thank you tulamide for passing on this report. I wondered why the streets seemed unusually deserted. The paper failed to mention my Phaser so I have something to be grateful for.

Cheers

Spogg

[KG_is_back]

like... seriously? :D:D:D

[Spogg]

Quilcom IRA: Impulse Response Author

This topic is so fascinating that I felt it might benefit from something orange

Based on all the info you guys have given me I now have some idea of the process, so many thanks for that.

I've made a synth dedicated to creating stereo reverb-like sounds, or, if you so wish, gunshot samples.

I hope it's easy to pick up what to do and I've made some presets and saved some IR wavs which are in the zip. Try them and see what you think...

What really blew me away were the results in Martin's Demo convolution reverb. With this Quilcom you can make custom reverb-like sounds then hear the effect on real audio. Unbelievable! It would take forever to program a conventional reverb, if it were possible to do this stuff, but it's so easy to make the sound of the reverb first.
BTW I loaded a 5 second sample and it worked and sounded good!

Notes:
The On time should ideally relate to the graphic envelopes. This will affect the repeat which is there to assist adjusting the system only, to save keep hitting the FIRE button.
If the green LED, which shows the On time, is lit then you won't be able to FIRE the impulse but it will re-start the timer. So, wait until the LED is off then you can FIRE single hits.
Set a recording time to be just above the the envelope time. Press the Arm button then FIRE the impulse. Then tap the Save button to save the impulse you just recorded.
The Parametric EQ only affects the tail and the idea is to simulate a resonant enclosure like a small room or speaker box for example.
The dynamic filters can be used to simulate reverb damping and many other effects.
The original impulse and tail can be mixed to taste and the stereo width can be set.
What you hear is what gets recorded.

Please use this or modify it as you wish.

Cheers

Spogg

[tulamide]

I will have a look tomorrow, erm I mean later this day. If it works as I assume it would be an awesome tool for generating unusual IRs (depends on what exactly you can create, just fast delayed echos won't offer much versatility). Hopefully a good toy to go along with the convolution engine!

[tulamide]

My first impression is not so enthusiastic. The tool itself is really good, with a lot of options to play with and create filtered noise. But the results are of bad quality compared to other IRs. I will try to save the impulse as an isolated second wav and de-convolve the files. Maybe the quality gets better then.

[Spogg]

My first impression is not so enthusiastic. The tool itself is really good, with a lot of options to play with and create filtered noise. But the results are of bad quality compared to other IRs. I will try to save the impulse as an isolated second wav and de-convolve the files. Maybe the quality gets better then.

No probs!
If you can suggest ways that I can improve on this I would love to try and implement them. For me this is open ended and this was a first stab so... bring it on!

Cheers

Spogg