What is the difference between silent subliminal and high pass filter? I used both, in silent subliminal the waveform is big, in high pass filter, the waveform is small. But both are inaudible sometimes.
If both achieve the same purpose, what is the need for silent subliminal?
I have a request in for notes on the Audacity Silent Subliminal process. I can’t tell which process we settled on.
High Pass Filter is pretty simple. Depending on the setting, it just removes low and/or medium pitch tones from the file. Traditionally, it’s used to remove rumble, earthquake, thunder, thumping, and breath sounds from a performance. A more extreme example does that and also “tightens up” the voice making it sound like a voice played on a phone. All the way up and it removes everything except tongue-ticks, lip smacks, mouth noises, and background hiss. So it doesn’t “convert” the message to anything useful.
You can’t derive a message from it and you can’t reverse it.
More as I find out.
Koz
A traditional high-pass filter reduces the signal level more, the farther down you are from the cutoff frequency.
Depending on the cutoff frequency and the sharpness of the filter the audio could be completely lost… Essentially “rounded down” to zero. A 16-bit file goes down to -96dB and a 24-bit file down to -144dB if you go lower you get sample values of zero which is digital silence or-infinity dB. (When you play a dead-siand lent digital file there is analog noise so you don’t actually get -infinity dB bust there is no digital audio.)
I see two programs available. One produces Single Sideband in a “sound” pitch above natural voice tones and the other one is a mystery. Apparently, the SSB one is based on existing, published subliminal process and experiments. It’s also based on known electronics, and not magic.
Fair warning, that these processes demand that you have a sound system that can deal with ultra-sonic sound—dog whistles. You know that thing when your dog suddenly wakes up and starts barking frantically and charges for the door—but you can’t hear anything? Those sounds.
As we go.
Koz
This is the silent subliminal code I’m using. What is the difference between output produced by this and high pass filter? This doesn’t demand any ultra sonic, 20KHz is well within the audibility range and frequency range of most earphones, headphones and speakers. The reason the output is limited to within 20KHz is because treble becomes inaudible as people grow old.
;nyquist plug-in
;version 1
;type process
;name "Subliminal..."
;action "Subliminal..."
;control carrier "Carrier" real "Hz" 17500 14000 20000
(setf carrier (max 14000 (min carrier 20000)))
;; We have two Nyquist frequencies, carrier/2 and *sound-srate*/2.
;; The CUTOFF is the maximum allowed frequency in the modulator.
;; It must not be greater than carrier/2, but also not greater than
;; the difference between the carrier and *sound-srate*/2, because
;; otherwise the modulated carrier aliases.
(setf cutoff (min (/ carrier 2.0) (- (/ *sound-srate* 2.0) carrier)))
(defun cut (function sound frequency)
(dotimes (ignore 10 sound)
(setf sound (funcall function sound frequency))))
(defun subliminal (sound)
(let ((result (mult 2 (cut #'lowpass8 (hp sound 80) cutoff)
(hzosc carrier))))
(cut #'highpass8 result carrier)))
(if (< *sound-srate* 44100)
(princ "The track sample frequency must be minimum 44100Hz.")
(multichan-expand #'subliminal s))
Bingo. That’s the software I got using a different path. Now all I need to do is run it and see what happens. My goal is to be able to reverse it.
I need to drop for a while.
Koz
I downloaded the module and installed it for testing, but it didn’t do what I was expecting. Actually, beside creating a blank track, it didn’t do anything. I think I have enough notes now to start actual troubleshooting.
Question. When you use the software, what does the timeline look like? The original mono track on top followed by what looks like the same track you can’t hear?
I can’t predict what the SSB track is going to look like.
Koz
After using the silent subliminal script, the track is transformed, with the wave form showing slight decrease in amplitude and plot spectrum showing it occupy frequency range 3000Hz above and below the chose frequency.
Thank you. I did get it to work enough to reveal some basic electronic problems.
The script depends on the operator strictly adhering to the specifications as presented. You can’t use a video sound track at 48000 sample rate. It must be Audio CD standard of 44100. This is me writing that down.
I am writing to another form poster and it might be useful for you to join that conversation.
!@#$%^
This was so much easier in the old forum software.
Koz
I’m participating in that thread as well.
Thanks to Steve TF a senior forum elf for helping out. He can speak Nyquist and he unscrambled some of the oddities and apparent missing pieces in my experiments.
There is one safety consideration that has to do with playback volume. This isn’t posted anywhere, but I suggest a small sample of “real world sound” be included before the subliminal material. Set your headphones or sound system for comfortable listening and then let it sail right into the affirmations or “Stop Smoking” message.
Koz
You haven’t yet posted your script. If you do, I can compare it against the one I posted.
;nyquist plug-in
;version 1
;type process
;name “Subliminal…”
;action “Subliminal…”
;control carrier “Carrier” real “Hz” 17500 14000 20000
(setf carrier (max 14000 (min carrier 20000)))
;; We have two Nyquist frequencies, carrier/2 and sound-srate/2.
;; The CUTOFF is the maximum allowed frequency in the modulator.
;; It must not be greater than carrier/2, but also not greater than
;; the difference between the carrier and sound-srate/2, because
;; otherwise the modulated carrier aliases.
(setf cutoff (min (/ carrier 2.0) (- (/ sound-srate 2.0) carrier)))
(defun cut (function sound frequency)
(dotimes (ignore 10 sound)
(setf sound (funcall function sound frequency))))
(defun subliminal (sound)
(let ((result (mult 2 (cut #'lowpass8 (hp sound 80) cutoff)
(hzosc carrier))))
(cut #'highpass8 result carrier)))
(if (< sound-srate 44100)
(princ “The track sample frequency must be minimum 44100Hz.”)
(multichan-expand #'subliminal s))
Koz
Note there is a handful of changes and cautions to get this to work. You can’t just dump an unfiltered, noisy, distorted sound file in there and you’re done.
As before, I’ll post a detailed How-To when we finally pull off a beginning-to-end test.
Koz
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