The dbx 120X and I think the 500 before that are subharmonic synthesizers that artificially create music an octave down from the show. I use it to simulate stepping on organ pedals when I don’t have organ pedals.
It takes bass notes around and above 120 Hz and creates new tones centered roughly at 28, 34, 40, and 50Hz.
Nobody is likely to step on four pedals at the same time, so dividing up the bass spectrum like this is relatively safe. Even if you do digital division, simple filters at that frequency will turn everything back into sine waves anyway.
The acoustic effect is that of pulling out the 16’ stop. Suddenly you have music that makes your shirt move – assuming your speakers are up to it. The electronics are continuously variable, so it’s not exactly like pulling out a pneumatic stop and suddenly there it is. Just like a real organ and church, I can tell you which notes cause my listening room to rumble.
I wonder what would happen to someone’s voice in this device. I wonder if this wouldn’t help all those people looking for that “pro announcer voice” and can’t get the PAF to work right.
Then, if I can get it to work in hardware, try to make it work in software.
sort of like an exciter in the other direction
even if 3 of those freqs are not true subharmonics
which makes me wonder why they didnt use all true subharmonics
(60 30 20 15 and the 40 you noted)
they must have had a reason to offset them
easier hardware design?
The frequencies are set to cover the bottom octave (below fifty something Hz), so the range from lowest synthesized tone to highest needs to be within a doubling of frequency. Using exact sub-harmonics would produce a ‘bumpy’ output with certain notes from the input producing much higher output (if harmonically related to the synthesized tones) than other notes (not closely harmonically related).
The chosen frequencies are approximately equivalent to a major 7th chord on the note of A0, which gives very even coverage of the audio spectrum within that octave range, so the device will always be able to produce a tone that is close to a true sub-harmonic, for any frequency from the octave above. Pitch recognition at extreme low frequencies is much less acute than in the normal “melodic” range, so the fact that none of the synthesized tones are exactly in “concert pitch” is not important from the standpoint of harmony/dissonance, but is an important factor in producing an even amount of sub-bass across the octave.
At one time these were quite popular with discos, but would often sound really bad because of the uneven frequency response of the disco “scoop” bass bins, coupled with the fact that they need to be carefully tuned for the room (the wavelength of sound at these frequencies are around 10 meters so it is really easy to set up standing waves in large rooms).
(scoop bins are not always “bad”, but they never have an even bass response - I think they can sound great for dub reggae)
Exactly correct. I have a brochure where they claim “dbx Disco Products.”
And yes, it’s never quite perfect because of the delays. Actual 16’ diapason or flute pedals are played slightly ahead to give the Diesel generators behind the loft time to crank up.
Sub Bass generators can never achieve good timing because they’re always two bass note structures late. One to figure out there was a bass note there to begin with and then the process to make a new, lower one and get it out the door. The show, bass and sub-bass can never line up in real time.
I need to try this. Where’s my microphone…
OK, well. The results are in and they’re about what I would expect had I thought about it for any amount of time. Far from making me sound like A Famous Announcer, it made me sound like Koz with a truck going by – and you could only hear it if your speakers went down that low. All that and the effect is only triggered when my original voice goes down into range. Back to the drawing board.
I did get tracks good to mess with like recreating that delay effect mentioned.
I did notice one other thing while I was recording the dbx machine raw. I don’t think they bother to filter out the higher harmonics. The recording I got is seriously unstable. Sometimes it plays cleanly and sometimes with terrible distortion. If I do a spectrum analysis, some of the energy goes up past 20 KHz and just keeps going. Since 44100 can only handle up to about 17 KHz without tricks, I suspect that’s what’s going on.