Hi Reverb Lovers!
Recording IRs with Zynthian is something i wanted to try from a long time ago. The goal is recording an post-processing IRs from the zynthian-ui, so you have the IRs ready to use without leaving the zynthian-ui.
A few days ago we (@zylvio and @jofemodo) was allowed to make an IR recording session in the “Teatro Fortuny” in Reus (Spain), and we wanted to take profit from this opportunity, so we prepared the session carefully and added some extra option to zynthian.
First, I would like to introduce the theater:
As you can see, a nice piece from end of XIX century.
We decided to record as follows:
- 3 points at different distances in the center corridor.
- For each point, we would do 4 recordings:
- sine sweep, stereo recording with a pair of little capacitor mics
- sine sweep, mono recording with an omni-directional microphone (AKG)
- clap, stereo recording with a pair of little capacitor mics
- clap, mono recording with an omni-directional microphone (AKG)
The sine sweep would be generated by zynthian and played using the theater PA. We didn’t want to over-complicate things by carrying our monitor speakers, or ideally, an omnidirectional flat-response speaker set that we don’t have, so we prefered to go the easier way and capture the “PA character” in the sine-sweep IRs. It would be nice to compare with the “clap” generated ones.
The exciting sinesweep generated by zynthian and the audio from mics would be recorded in the same multi-track audio file, perfectly synced to the sample, so post-processing this would be really easy. Simply deconvolve both signals to get the IR, with minimal (or none!) human intervention.
Regarding the clap, it was generated by simply clapping hands from the stage. No perfect, but it was a first try and none of us had previous experience, so we thought that it would be fine to start using the more “basic techniques” and learn from the beginning. Post-processing this would need some human intervention to “crop” the audio signal.
As pre-amp we would use a Focusrite Scarlett 2i2. Good enough for this first try.
We met at 16:00, with a totally empty theater and quite silence. So, here we go with the recording session!!
I was all the time in the control room, near the roof:
Silvio was in the pit, placing the mics and clapping hands 
The session was quite fast and with little issues, excepting our initial problems to get the sine-sweep going through the PA. Indeed, we finished before the 2 hours we was allowed to use.
Here is the snapshot i used for the sine-sweep generation + recording:
015-Sweep-response-recording.zss (7.5 KB)
Results
I have added a new “deconvolve” option to zynsampler that allow to post-process multi-track recording files to obtain the final IR. It assumes the tracks 1 & 2 contain the exciting signal as generated by the source (in this case, a 10 seconds sine-sweep), and the tracks 3 & 4 contain the audio recorded from the microphones. To ease things, we duplicated the signal from the omnidirectional microphone, so all our recording files could be processed the same.
With this “deconvolve” option we got totally usable IR files from the sine-weep recordings. They had some weak ghost harmonics in the tail, but perfectly usable and quite nice.
This is an example IR:
obtained by deconvolution 100% with zynthian, without any human intervention.
Anyway, for the final IRs, i have removed the ghost harmonics by cutting the long tail.
(ahh! this new deconvolve option is available now in Vangelis branch)
For “cropping” the claps, i copied the files to my desktop computer and used Audacity to crop the audio wave. With these recordings, the noise-floor added a kind of “continuous reverberation” in the tail. Reducing the noise and adding a fade-off to the end, fixed the problem.
And nothing more. Here the final 12 x IR files:
jofezylvio_Fortuny_theater-IRs.tar.xz (9.5 MB)
For using the IR files, i recommend the X42 convolver plugin, from the reverbs category. You probably need to reduce the default wet level (-25 to -35dB) and increase dry level (0 to 2dB or so).
Do you want to hear it? OK 
This is a little hammond reef, switching the reverb on each loop. The 2 first loops are dry, same than the last one. Some loops are a bit saturated because i had no time to reduce the wet level on these ones while recording. I recorded this on a single pass, sorry.
In general sweep-generated IRs are more louder and bass-richer. Clap-IRs are more high-pitched and omni-directional sweeps have the more bass.
Enjoy!