Silent Subliminal Recording

[MikeM3]

Audacity and to this forum are new to me, so I hope that someone can advise me.

I am using Audacity version 2.0.6 and XP Pro SP3.

I would like to make some silent subliminal recordings for educational purposes but I seem to have got lost in the process.

Reading the previous threads on this subject only added to my confusion as there were snippets of code in the replies and other suggestions that were for earlier versions of Audacity, v1.4.??

I added some audio, not mine, but a prerecorded item and set the output (I think) to 16500 hz, then I exported it as a WMA file.

When I opened the file in windows media player, I could still hear the audio at the set volume!

Should I try to play it on a machine that doesn't have the original on it, or is there something, (probably a lot), that I haven't done?

Any help or suggestions will be gratefully accepted.

Thank you for reading this.

Mike.

[DVDdoug]

You didn't say what you did to make the recordings "subliminal".

I would like to make some silent subliminal recordings for educational
purposes but I seem to have got lost in the process.

Silent??? You can create a totally silent file by clicking on Generate -> Silence, but a silent file doesn't contain any subliminal information...

If you simply want to reduce the volume, you can use the Amplify effect. Maybe try -60dB or so. If you can still hear it, reduce it more.

The problem is, if you are not controlling the volume the user can turn it up or re-amplify it to the point where it's audible again.

If you want to prevent that, you can mix the very-quiet subliminal message with normal music or pink/white noise.

Or if you are controlling the volume and you simply want to make sounds nobody can hear, you don't need to make a special file... Just turn-down the playback volume to the point where nobody can hear it!

...then I exported it as a WMA file.

WMA, MP3, AAC, etc. are lossy compression formats. They work by throwing-away stuff you can't hear. Specifically, they work by throwing-away sounds that are masked (drowned-out) by other sounds. Your experiment may be invalid if the subliminal information is thrown-away. WMA encoding shouldn't bring-back stuff you couldn't hear before.

16-bit WAV files go down to about -93 or -96 dB, and any audio below that level will be lost if you save as 16-bit WAV.

[steve]

You didn't say what you did to make the recordings "subliminal".

He didn't, but my guess is that he wants to emulate Lowry's silent subliminal presentation system (US Patent 5,159,703 October 27, 1992).
http://www.google.co.uk/patents/US5159703

If that is what you are after Mike, then see this post: http://forum.audacityteam.org/viewtopic ... 08#p138508
That was written for Audacity 1.3.13 but it applies equally to the current 2.0.6 version of Audacity.

[MikeM3]

Thank you Gentlemen for the swift replies.

DVDdoug, you said that I didn't say what I did to make it subliminal. Having only been using the software since 15th October, I used the only thing/place I could find that had any indication of Hz is at the bottom left of the screen called "Project Rate (Hz)", this is where I typed 16500 in the window.

Thank you for the information about WMA, MP3 and AAC, I read about the MP3 & AAC, but thought that WMA was OK.

Steve, you are correct in the assumption that I am trying to get the message across in a non irritating manner as Mr. Lowery so clearly explains in his patent application.

I have read the contents of your link to the that you answered to in 2011, in fact I read it before I asked the question.

You give two pieces of code to apply to the project and these are what frightened me slightly, but having read them again I feel comfortable with them and your instructions are very clear.

The settings are different from the ones that I have read about, most of the places that I looked at on the internet suggest that the output frequency should be 16.5Khz, so I assume that I need to type in two numbers that are, one higher and one lower than the target one.

In your first piece of code, you add a warning that the high frequency is liable to burn out speakers, I can't have that as others will be using my end product in their home, I hope, so I will have to go for the lower numbers.

According to the statements made by others, the silent output will not disturb or bore anybody who is within "Hearing Range" of the player, you won't hear anything with your ears, but they will still pick up the output, even if it is covered/masked by another audible sound such as waves at the shore, birds tweeting or even any music.

These messages, if I am successful will help a group of people to learn Spanish.

Thank you once again for the help you have given me so far, no doubt I will be back for more till I become familiar with the program.

Mike.

[steve]

The settings are different from the ones that I have read about, most of the places that I looked at on the internet

That particular code provides a close approximation to Lowrey's method. There are many other ways to implement the same (or similar) technique.

If you care to search the forum, there is a plug-in by "Edgar-rft" that simplifies the process. (there may also be one from me, but this was all a long time ago )


The risk regarding burning out speakers and hearing damage is particularly to do with using the "silent sound" on its own.

Typically, "real world" audio has very low energy at extreme high frequencies.
If you look at the spectrum (see: http://manual.audacityteam.org/o/man/plot_spectrum.html) of normal sound, you will notice that very high frequencies drop off in amplitude quite considerably compared with the main "audible sound".

With synthesized signals, it is possible to produce very high frequencies with very high amplitude, and this is where it can start getting risky.
If you generate a tone at 18000 Hz and play it back at "normal volume", then it will either sound extremely quiet, or totally silent. Although the generated tone is much bigger than would be found at that frequency in "real world" sound, I do not think it is likely in itself to damage either the equipment or your hearing (but note that I am not a doctor!) It is probably not good to play high amplitude extreme high frequencies for extended periods - the equipment is not designed to do that.

Because it is silent, or virtually so, then the temptation is to whack up the volume to make it "louder". This is where the risk to equipment becomes significant (and possibly a risk of hearing damage - I don't know, but I wouldn't risk it and I accept no responsibility if my warnings are ignored )

So the question is: "As I can't hear this "sound", how do I know how "loud" it is?"
This is not actually the right question. "Loudness" is subjective. Something is "loud" if it "sounds loud" or is "quiet" when it does not "sound loud". The correct term is "amplitude" (or "level"). We can tell how "big" an isolated tone is (how great the amplitude is) by looking at the waveform. The vertical height of the waveform indicates the "amplitude" (also called "the signal level").

If your "silent sound" is mixed with normal sound (apparently a common technique with "silent subliminals"), and the normal sound has a significantly higher amplitude than the "silent sound", then that should protect both the equipment and the listener's ears because they will not want to turn up the playback volume to extreme levels (because the audible sound will become so darned loud )


I'm no expert on the efficacy of "subliminal messaging", but having read a bit about it, there is very little documented evidence that Lowrey's method works at all. According to scientific research (of which there is lots because it has huge financial implications in terms of advertising and propaganda), the most effective form of audio subliminal messaging is extremely simple - the "message" is played at a volume level that is at the threshold of hearing. In other words, all you need to do is to turn down the playback level until you can barely hear what is being said. This technique is not favoured by people wanting to sell "silent subliminal products" for obvious reasons - it's too easy and anyone can do it.

[MikeM3]

Thanks again Steve for your reply.

Having read your words and the content of the links that you provided,
I have come to the conclusion that I don't know enough to be even called
a novice, I am completely ignorant about sound!

I didn't think that this type of recording would be so complicated.

This is not just clicking a button or two to get the desired results.

Can a sine wave be see after the effects have been carried out
successfully?

Has anybody in the past been successful with a project like this?

I going to be busy for a couple of weeks anyway, after which I will
have a lot more time to try again.

Thank you for your help and advice.

Mike.

[steve]

This is not just clicking a button or two to get the desired results.

Here is the topic and the plug-in that I was referring to previously: http://forum.audacityteam.org/viewtopic ... 86#p148686

Using the plug-in should make it easy to create "silent subliminals".
Instructions for installing plug-ins are here: http://wiki.audacityteam.org/wiki/Downl ... g_Plug-ins

[MikeM3]

Thank you once again Steve.

Mike.

[sydsrich26]

Thank you Steve.

I have purchased subliminal recordings and not been sure they were for real because despite how loud I played them there was no signal in the output level to show they were generating sound. But today I followed your instructions and while I can't hear anything I can see by the output levels sound is coming out. Prior today all I did was turn the amp down as far as it would go and that seamed to vaguely work. Thank you again.

Syd

[sydsrich26]

Hi

Somehow a couple of weeks ago I managed to download a subliminal plug in from here. I proved it worked and left it until I needed it (NOW) but when I click on subliminal in the effects menu I get the box saying "carrier 17500 (which can be adjusted) I click on ok and then I get (I assume) an error message "Die samplefrequenz der tonspur muss mindestens 44100Hz sein" . Can you help?

Regards Syd