Reverberation Concerns with Fluidsynth 2.2.8

[JOHNjORGAN]

jOrgan, an Open Source Virtual Pipe Organ program, makes extensive use of Fluidsynth as our sound engine of choice. Reverberation is very important to us. Whilst we are pleased with the improved quality of the reverb sound in Fluidsynth 2 compared with FS 1, it is marred, at least for our use, by a cyclic modulation at a rate of about once each second. It does seem to be a modulation of amplitude rather than pitch.

I am sending this in the hope that developers can address this matter. (Sorry - the Title should be version 2.2.8)

Best wishes,
JOHNjORGAN

[derselbst]

Yes, there is a vibrato effect. This is intentional, see

fluidsynth/src/rvoice/fluid_rev.c

Lines 256 to 273 in e64ad84

	/*-- Modulation related settings ----------------------------------*/
	/* For many instruments, the range for MOD_FREQ and MOD_DEPTH should be:
	MOD_DEPTH: [3..6] (in samples).
	MOD_FREQ: [0.5 ..2.0] (in Hz).
	Values below the lower limits are often not sufficient to cancel unwanted
	"ringing"(resonant frequency).
	Values above upper limits augment the unwanted "chorus".
	With NBR_DELAYS to 8:
	MOD_DEPTH must be >= 4 to cancel the unwanted "ringing".[4..6].
	With NBR_DELAYS to 12:
	MOD_DEPTH to 3 is sufficient to cancel the unwanted "ringing".[3..6]
	*/
	#define MOD_DEPTH 4 /* modulation depth (samples)*/
	#define MOD_RATE 50 /* modulation rate (samples)*/
	#define MOD_FREQ 1.0f /* modulation frequency (Hz) */

I don't like it too much either. To address this I was thinking about making the reverb engine configurable. I.e. re-introduce the old freeverb engine and an additional Lexicon-like reverbator. To do so, I would like to rewrite the current reverb implementation to a C++ abstract class hierarchy, to make it easy implementing more reverb engines. But so far I had no time to do so.

[JOHNjORGAN]

Thank you very much for your reply, which explains it all. I have conveyed this information to the jOrgan Mailing List. It is clear that the type of music and the reverb settings make a big difference to how intrusive that modulation is. There is no doubt that the use of this technique has produced a better sound for most users. There is much less "selective" ringing.

[moonskin]

I have also worked with jOrgan but mostly with Miditzer.

To say this "effect" is "intentional" is, to me, saying that there is a bug here that is unresolved. Any reverberator that adds an unwanted modulation to a steady tone is faulty. This needs to be fixed IMO. I would be inclined to report it as a bug if I could see how.

Regards
Graham

[derselbst]

Any reverberator that adds an unwanted modulation to a steady tone is faulty. This needs to be fixed IMO.

I welcome your PR.

[jimhen3ry]

I have submitted this as Issue #1215 on behalf of moonskin and JOHNjORGAN.