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Phantom Signals


The Phantom Signals phenomenon is an auditory hallucination of a "radio station" nearly obscured by noise. It can be reliably produced in normal subjects using only a low-level broadband noise stimulus, delivered to one ear only via headphones in a quiet room.

After a few minutes of listening, faint music and/or speech is heard, in an ongoing non-repeating stream reminiscent of a radio station. The program volume seems to be just a bit too low to hear distinctly against the background noise, but there is a strong sense that a real signal is present.

A certain style of music may be heard, but not clearly enough to identify the particular song, nor to catch the actual melody. An "announcer" may be heard, possibly identifiable as male or female, delivering what may sound like a news broadcast or a commerical. But the words are never distinct.

The perception is so compelling that some people are convinced that the sound system must be picking up leakage from a nearby radio station, and may insist that there is something wrong with the equipment... perhaps a faulty ground shield.

But when the same noise stimulus is then presented equally to both ears, the "program" instantly vanishes. This would be very hard to explain if the noise was actually contaminated with a radio signal... if that were the case, the same program should then be heard with both ears.

Some may suggest that perhaps only one output channel is defective, or only one earphone, and that when both are active the good one overwhelms the defective one. That can be easily disproven by switching channels and reversing the earphones, and noting that the phenomenon is still present when listening to the supposed "good" channel and/or earphone.

The Phantom Signals phenomenon is apparently undescribed in the scientific literature, so almost anything you do can be original work. Your experiments in this area might make a great science fair, honors, senior, or masters project, or even a doctoral thesis.


The Phantom_Signals macro mini-app that is included with Daqarta allows you to experience this phenomenon for yourself. To run it, hit the F8 key followed by the 'S' key, or hit CTRL+F8 to open the Macro Dialog and double-click on Phantom_Signals in the Macro List. You should be in a quiet room, using headphones.

The macro uses a Custom Controls dialog to allow setup and adjustments. (Grayed-out controls at the top of the dialog are for advanced experiments with different noise types instead of the default White. These will be explained later, under Experiments With Noise Types.)

Note that you can open this Help topic at any time by right-clicking anywhere in the Phantom_Signals control dialog.

Toggle the Setup button on and Daqarta's volume slider dialog will open, along with a message telling you to "Adjust volume for pulsing noise threshold. Then toggle Setup off for 30 dB above threshold."

The noise is amplitude modulated during Setup, and sounds somewhat like a steam engine. The pulsing allows you better distinguish the noise from the background. Adjust the volume sliders until you can just barely hear the noise, which will be in your left ear only. (You may have to reverse the phones on your head. This is only so that your setup will match the Left Only button... see below.)

When you toggle Setup off, the noise will become steady, and 30 dB louder than your hearing threshold for the noise. That loudness is not critical, just a good starting point.

Now keep listening. It may take several minutes, but the Phantom Signals will eventually become evident. (After you have a little practice the phenomenon will appear much sooner, sometimes in just a few seconds.)

Click on the Both Ears button. There will be a brief delay (about 2 seconds) before sound appears in both ears, but as soon as it does the Phantom Signals will instantly disappear. (See Left / Right Output Enable for an explanation of the delay. There is no lag when you toggle Both Ears off.)

You may find that one ear is better than the other at hearing the Phantom Signals. To switch ears, you can either reverse your headphones, or just click on the Left Only button and it will change to Right Only. Again, there will be a brief delay before the sound shifts.


What causes the Phantom Signals phenomenon? One possible explanation is that the "signals" are random features of the noise which just happen to be vaguely similar to speech or music. The brain then perceives real signals, in the same way that we can see animals or faces in cloud formations. This is called pareidolia.

But if the Phantom Signals are produced by features that are actually present in the noise, then why would listening to the same noise in both ears cause the illusion to vanish?

Also, if there are specific noise features that correspond to words or musical notes, then one might expect that if the identical noise sequence is repeated, containing exactly the same features, we should have a similar illusion each time. For example, if the first presentation sounds like Country music followed by a news broadcast, then we should hear that on later repetitions... we should not hear an emphatic commercial followed by Heavy Metal.

Daqarta allows you to repeat the identical noise sequence, and when this is done there seems to be no correlation with prior repetitions. An exact repeat produces no different experience than simply continuing with new previously-unheard random noise. This would seem to argue against there being any specific features in the noise sequence that are provoking pareidolia.

You can repeat the noise sequence just by restarting Daqarta. Since the Randomize option for the noise source in Stream 0 of Phantom.GEN is set to Independent, the sequence repeats exactly on every session. It will produce a series of random values that doesn't repeat for as long as you run it (assuming you don't run it longer than about 6 million years!), but when you restart Daqarta it will repeat the same sequence exactly.

Alternatively, you can arrange for the sequence to restart each time a button is clicked. First, click on the Left Wave Controls button in the Generator dialog to open the Stream 0 controls. Near the upper middle is a button labeled Smooth TC, which opens the Timing dialog. (The Smooth TC button replaces the Tone Freq button when Wave is set to one of the Noise types, which in this case is White.)

Near the bottom of the Timing dialog is the Randomize button, set to Independent by default. Click on that to open the Randomize control dialog, then click on Copy 1 under Left.

This copies the Stream 1 random sequence generator into Stream 0. Note that Stream 1 is not active in Phantom.GEN, so its sequence generator is never updated. That means that every time you click that Copy 1 button (even though it stays depressed), the identical original unchanged Stream 1 generator is copied to the active Stream 0, repeating the noise sequence exactly from that starting point.

(Setting Randomize 0 instead of Copy 1 will seed the Stream 0 random generator with new, unpredictable values. If you save the changed Generator setup, then Stream 0 will be randomized automatically every time that setup is loaded.)

Other Auditory Hallucinations:

Auditory hallucinations are common in schizophrenia, but those are almost always speech, not music. The speech is often distinct, typically specific commands or threats. By comparison, the Phantom Signals phenomenon is experienced by normal people, is always indistinct, usually includes music as well as voices, and the voices are not reported as commands or threats.

Auditory hallucinations are also experienced by normal people, typically those with some hearing loss, or those on certain medications like beta blockers or high doses of aspirin which cause tinnitus. (Tinnitus is the perception of noise or tones that arise internally, usually audible only by the subject. Tinnitus is most often due to spurious neural activity, but occasionally to mechanical noise caused by blood vessel restrictions or jaw problems, for example.)

Curiously, these hallucinations are most often patriotic or religious songs that are distinctly heard, and often repeat multiple times.

There are also a few reports of distinct songs heard by normal people in environments where there is prolonged loud external noise, such as in jet aircraft. This is apparently not very common, considering the number of air passengers.

These musical hallucinations may be analogous to the visual hallucinations of Charles Bonnet syndrome, which arises in people who are losing their eyesight (from macular degeneration, for example). A common explanation is that when visual input is greatly reduced, the brain sometimes "fills in the gap" with images from memory.

A similar explanation has been proposed for musical hallucinations, where normal auditory inputs are suppressed by hearing loss, or masked by external or drug-induced noise, and the brain compensates by "playing back" old songs from memory. (The reason for the prevalence of patriotic and religious songs is unclear.)

On the other hand, the fact that Phantom Signals are indistinct seems to preclude memory playback as an explanation. Phantom Signals are also suppressed by the presence of noise in both ears, unlike the above musical hallucinations in noisy environments.

Pre-Classification Error:

Phantom Signals may arise due to a quirk in the way sounds are classified by the brain. Before a sound is identified, there are a number of pre-processing steps that take place. In the earliest steps, inside the cochlea, the sound is decomposed into its various frequencies and amplitudes. In effect, there are separate neurons for each frequency we hear, whose firing rates are determined by the strength of the sound at those frequencies. (The cochlea essentially performs a mechanical Fourier transform as it converts from sound waves to neural firing patterns.)

Further information is extracted as the neural impulses proceed to successively higher brain centers. For example, there are neurons that detect upward and downward sweeps of frequency, which are important components of speech.

The actual identification of particular words, phrases, or melodies is clearly a high-level process, but it might be preceded by a preliminary classification that merely decides if there is any speech or music present, without specific identification. This might serve to alert higher-level systems that they need to attend to the incoming sound.

This preliminary classifier might be part of a more primitive system for directing attention to important sounds. Our ancestors would certainly have needed to tell the sound of an approaching predator from the sound of wind-blown leaves, or an infant's cry of distress from a creaking tree branch. The faster such distinctions could be made, the better the chances for survival.

Stewart Elliot Guthrie, in "Intelligent Design as Illusion" (Free Inquiry, Vol. 26, No. 3, April / May 2006) observes that perception is always uncertain, and proposes that the brain uses a strategy where "in the face of uncertainty, guess first at the most important possibility." The preliminary classifier model for Phantom Signals would seem to fit well with this general concept.

The preliminary detection might prompt head re-orientation toward the noise (the better to see as well as hear it), to allow the higher-level brain centers to make a final fight-or-flight judgement. Or, in some cases the preliminary detector might even prompt an immediate flight response, without waiting for the high-level centers to be absolutely certain about the origin of the sound. After all, it is far better to be teased for being startled by a mouse, than to be eaten by a tiger because you waited to make certain the threat was real.

In natural environments, broadband noise (like wind, rain, rivers, and waterfalls) is never limited to just one ear as in the Phantom Signals protocol. So, perhaps the preliminary classifier gets confused. Could this sound be, say, someone whispering into one ear? Forced to decide if the sound is unimportant background noise or a possibly-important speech signal, it may "play it safe" and give a false alarm that primes the higher brain centers to expect speech.

But the Phantom Signals phenomenon also includes music as well as speech. It could be that the preliminary classifier is attempting to detect any kind of information, not specifically speech. This seems likely if the classifier evolved earlier than speech or music, as part of a more general system. So when it gives a false alarm, it is really announcing the presence of a signal that needs to be interpreted by the higher brain centers, which then make the actual speech-versus-music decision based on arbitrary criteria.

Radio Station: Suggestion or Innate?

Why do Phantom Signals induce a "radio station" image, instead of simple speech or music... or other sounds? Under the "guess first at the most important possibility" model discussed above, speech might be the most important possibility. Yet there is no feeling that someone is speaking (or singing) in the same room, or even in another location through a microphone.

The radio image could be due to prior experience with radio broadcasts. When we hear speech or music through an earphone, we associate it with a radio. (If this is the explanation, then younger listeners may well associate it with an MP3 player.)

In addition, most people will probably also be aware that radio transmissions can sometimes interfere with other electronic equipment. (Even non-technical people will have been exposed to this concept from numerous movies and television shows.) Thus, when anything other than the original noise source is heard, the automatic assumption would be "some kind of radio interference". That might lead to the perception of a radio program.

Alternatively, the radio percept might be due simply to the power of suggestion, since that was used in the initial description of the phenomenon. If people who are unfamiliar with Phantom Signals can be made to experience something that is neither speech nor music, such as bird calls or traffic noises, that would point to suggestion as the determiner of the phenomenon. It would also tend to invalidate the entire explanation that Phantom Signals reflect an "important possibility" classifier.

One way to explore this might be to deliberately mislead test subjects by telling them that they are participating in an experiment on the detectability of various types of signals in a noisy background. The subjects could be tested in a room with conspicuous metal shielding, which they are told absolutely blocks all radio waves. This would hopefully reduce any tendency to assume radio interference.

Initially, the subjects would be presented with each of the possible test signals, a set which might include speech in their native language, foreign speech, various types of music, Morse code, police sirens, machine sounds, bird calls, and so forth. The test would then consist of random selections from the set, played at random times and at varying levels, along with a constant-level noise. Subjects would be asked to report whenever they heard one of the test signals, and to identify which it was.

They would never be explicitly told which answers were correct, but as they made more correct identifications, the signal level would be progressively reduced, while the noise remained the same. When they made mistakes, the signal level would be increased. Eventually, they would work their way down to some threshold signal level, which might differ for each sound in the set. At this point, the signals would be detected at no better than chance.

The subjects would then be told that they "are doing so well that the test is moving to the next difficulty level": At any time, they may get any signal from the previous set, or they may get completely new signals. But unknown to them, the true signals would simply be shut off... the experiment would then be running completely on Phantom Signals.

The initial set of test signals could be chosen to deliberately bias the test results. For example, suppose the set only included various bird calls, and the subject was told that the "next level of difficulty" might include any of these, as well as other bird calls. Would the Phantom Signals then be heard as only bird calls? Or would speech and music still be heard?

Experiments With Noise Types:

You can experiment with using different types of noise to induce Phantom Signals. The White button at the lower right in the Phantom Signals dialog indicates the current noise type. Repeated clicks cycle through Gauss, Pink, Band, and back to White.

When you change noise types the apparent loudness changes as well, so you may want to repeat the Setup procedure with each new type.

White noise has equal energy at all frequencies. To see this, make sure the Spectrum button in the Daqarta toolbar is toggled on. White noise has a uniform amplitude distribution, which means that the amplitude at each instant is random, with all values in the 16-bit range of the sound card being equally probable.

Gaussian noise differs from White in its amplitude distribution, having more low amplitudes and less high. The overall loudness is thus lower, but all frequencies are still equally represented so the spectrum remains flat. (Technically, that means it is still "white".)

When in Gauss mode, the Gauss Std Dev control in the Phantom Signals dialog becomes active. This allows you to adjust the standard deviation of the noise: At maximum, the distribution is almost identical to White. Lower values give a greater proportion of low amplitudes, so the volume is reduced. (Note that the effect is not linear, so the control slider is too sensitive to use for deviation values much less than one; direct entry is better.)

It turns out that our ears apparently don't detect amplitude distribution at all, only spectrum effects. Since the spectrum is unaffected, Gaussian noise sounds absolutely identical to White, just softer. If the volume is adjusted to match, they are indistinguishable. You can prove this for yourself via a special Generator setup that alternates between the two types while keeping the loudness the same; the noise sounds constant, with indetectable transitions. See Comparing Noise Distributions.

So it is unlikely that you will find any effects on Phantom Signals using Gaussian noise.

Pink noise has a "sagging" spectrum, such that as the frequency doubles the power is halved. (This may be clearer by viewing the spectrum in X-log mode, which you can toggle from buttons in the Spectrum or X-Axis control dialogs, or by hitting ALT+SHIFT+X.)

The Pink noise spectrum is closer than White (or Gauss) to what we hear in the natural world, as well as to long-term averages of music or speech. This may make it more "relevant" to the brain, and thus affect the Phantom Signals phenomenon.

Pink noise is also a crude approximation to the spectrum of jet engine noise. You can try this with the Both Ears option (and/or use speakers) to see if you are one of the few who can experience musical hallucinations from binaural noise. From the limited reports of this phenomenon, it is not clear how loud the sound must be, nor how long it takes before you can expect to hear anything.

When Band is selected, band-limited noise is active and the Band Rise Frequency, Band Fall Frequency, and Band Taps controls become enabled in the Phantom Signals dialog.

The default Rise and Fall settings are set to 300 and 3000 Hz, respectively, and Taps (steepness) is set to 64. This is a rough approximation of the human speech range, so it may be relevant to the Phantom Signals effect.

If you reduce or increase the band width, or move it up in frequency, what effect does this have on Phantom Signals?

If you set Rise higher than Fall, the spectrum will be otherwise flat but with a gap between those frequencies. Note that with Taps set to 512 (maximum) the sides of the gap become quite steep and the gap width can be made quite narrow. Are there certain frequency ranges that are critical to Phantom Signals, such that the effect fails if that range is missing from the spectrum?

You can also use Band mode to get different jet engine noise simulations than those obtained via Pink noise. Try setting Rise to 0 and Fall to 2000 Hz to get a deeper, rumbling jet engine sound.

Binaural Noise Experiments:

The following experiments involve different noise sources or levels to each ear. They can be done with Daqarta, but are not directly suported in the included Phantom Signals macro. You can use that macro as a starting point for your own modifications, or manually adjust the Generator controls while the Phantom Signals macro is active.

For the latter, start Phantom Signals in its default mode. Perform the Setup volume adjustment, and toggle that off. You should now have sound at 30 dB above threshold in your left ear only. Open the Generator dialog and toggle the Right output enable on, and Left Solo off.

You will hear White noise in both ears, but although the volumes and average spectra are the same, the sources are independent so the effect is quite different than having the identical signal in each ear... it's like "stereo noise". (Toggle either Dual button to hear the difference.)

It is known that when the same noise is presented equally to both ears, the Phantom Signals phenomenon is suppressed. What if it's not the same noise, just similar? What if the levels are different? What is the minimum level of noise to the other ear that causes suppression?

Make sure Dual is off. Click the Right Wave Controls to get to the Right Stream 0 dialog, and adjust the Generator Level for the Right channel. It starts out at 0 dB (maximum output level) by default; enter a large value like 100 (really -100 dB, but you don't need to enter the sign) to effectively shut off the right output. Now wait until you hear normal Phantom Signals from the left ear, and try setting louder right Level settings (less-negative attenuation) until the effect is suppressed.

(If you want to test the opposite ear, reverse the headphones. Don't use the Both Ears button in the Phantom Signals macro dialog.)

The above gives the suppression threshold when the noises are independent. To get the identical noise in both ears, but at reduced level in right only, Dual won't work: It just feeds the same signal to both outputs, at whatever level is set for that single channel and stream.

Instead, you can make the Right noise source track the Left. Click on Right Wave Controls again (if it's not already open) and then on Smooth TC to open the Random/Step Timing dialog. Near the bottom under Randomize click on Independent to open the Randomize dialog for the Right Stream 0 noise source. Click on Left Copy 0, and the Right channel will match the left exactly except for the Level setting.

Close the Randomize and Timing dialogs to get back to Right Stream 0, where the Level control should still be set from the independent-noise tests. Again start with -100 dB and wait for Phantom Signals, then see if they are suppressed at a greater or lesser attenuation than when the noise sources were independent.

Incidentally, Right Randomize 0 under the Timing - Randomize dialog will get it back to an independent noise source. If instead you hit Independent, that will indeed make it independent, but it will be starting from the copy of Left 0... it won't differ unless you change Timing Shift, for example, or apply timing modulation to the Shift.

However, that leads to another parameter to explore: The relative position of the noise source. With Right Stream 0 Level back at 0 dB, and with Left Copy 0 set, you will hear the same sound in both ears just as if Dual was active. Now, however, you can use Timing Shift to move the apparent position of the sound around your head. Positive values move it one direction, negative move it the other way. Does that affect the ability to get a Phantom Signals effect with equal-loudness noise in both ears?

Or, leave the Shift value at 0 and click the Shift button to open the Timing Modulation dialog, then toggle Mod On. The noise seems to move around your head, or back and forth through your head. (This can be very disconcerting!)

Returning to suppression thresholds, what if the frequency ranges of the two noise sources are very different? For example, suppose a low-pass noise is used to produce Phantom Signals, then a complimentary high-pass noise is applied to the other ear? How about a band-pass to one ear and a complimentary band-gap to the other?

In the Phantom Signals dialog, click the White button until it shows Band, and use the controls to set the desired signal for the left ear. Then in the Generator dialog click Right Wave Controls, then Wave, then click Band. Adjust the Rise and Fall frequencies as desired, then close the Band and Wave dialogs to get back to Right Stream 0 to adjust Level for threshold tests as before.


SETI Simulator: The Search for Extra-Terrestrial Intelligence (SETI) involves searching for signals among noise. If test subjects were presented with noise in one ear only and told to listen for possible signals, presumably they would encounter the Phantom Signals phenomenon. Would they perceive the typical "radio station" effect, or something more alien?

Electronic Voice Phenomenon (EVP): Students of the paranormal make recordings of ambient noise from "haunted" houses, then listen for "spirit" messages. If the playback is to one ear only, they would be expected to hear Phantom Signals. Will the effect be shaped by their expectations?

Dental Radio: A popular urban legend concerns people who can supposedly receive radio broadcasts through their dental work. However, this has never been verified, and there are only a few poorly-documented anecdotes (chiefly from Lucille Ball). But some kinds of tinnitus can produce noise in one ear. Perhaps this induces Phantom Signals, which are interpreted as real radio broadcasts.

Drug Interactions: Some drugs such as THC (marijuana) cause users to report more-vivid perceptions from otherwise-ordinary stimuli. Would such drugs cause Phantom Signals to be perceived as speech or music that was clear and distinct, instead of the typical indistinct signals?

Pre-Technological Societies: It is interesting to speculate what people from pre-technological eras might have reported for Phantom Signals: Voices of demons? Gods? Angelic choirs? Could these have been caused by tinnitus?

Musical Inspiration: If Phantom Signals include music with melodies that can't quite be identified, it may mean that there is just a "song-like" feeling, instead of hearing an unfamiliar melody. Nevertheless, could this still provide musical inspiration to composers?

Auditory Ink-Blots: Does the nature of the perceived Phantom Signals indicate anything meaningful about the listener? Could these be used as an auditory equivalent of the Rorshach test? Even though the Phantom Signals are indistinct, the listener may still distinguish between "sad song" and "upbeat newscast".

Phantom_Signals Macro Listing:

The Phantom_Signals macro uses a Custom Controls dialog to implement the various controls. The macro loads the Phantom.GEN Generator setup that will be acted upon by the controls. The controls are labeled and initialized, with Ctrl0 to Ctrl3 also disabled via Ctrl0="<D", etc. (These will be enabled later according to the Btn3 selected noise type.)

Then the Custom Controls dialog is opened while setting the _Phantom_Ctrls macro to handle control changes, using @_Phantom_Ctrls=Ctrls.

_Phantom_Ctrls returns to this Phantom_Signals caller when the dialog is closed via its OK or [x] buttons.

Ctrls="<<Phantom Signals"
Ctrl0="<<Band Rise Frequency"
Ctrl1="<<Band Fall Frequency"
Ctrl2="<<Band Taps"
Ctrl2="< 64"
Ctrl3="<< Gauss Std Dev"
Btn0="Left Ear"
Btn1="Both Ears"

_Phantom_Ctrls Macro Listing:

This macro runs in the background to handle changes to controls in the Custom Controls dialog launched by the Phantom_Signals caller macro. On any change, _Phantom_Ctrls is called with the Ctrls variable holding an event code to identify the changed control.

Ctrl0 to Ctlr2 are only enabled if Btn3 has been clicked to Band mode. The noise band lower and upper frequency limits are set directly from Ctrl0 and Ctrl1 if either of these is changed.

Ctrl2 sets the Taps (steepness) value of the noise bands, limited to powers of 2 from 8 to 512. Ctrl2 was set to be a "read-only edit" type via Ctrl2="<r(0,6)" in the Phantom_Signals caller, which also initialized integer variable UT=3.

Here, a Ctrls=2 event indicates that an up/down scroll button was clicked, so the +1 or -1 scroll value Ctrl2?u is added to UT. The sum is limited to 0-6 and sent back to the control, which updates the slider position. That, or a manual motion of the slider, causes a Ctrl2=h82 event which converts the integer 0-6 value into 8-512 to set BandTaps.

Ctrl3 (Gauss Std Dev) is enabled only in Gauss mode, and sets GaussSD directly.

Btn0 (Ctrls=4 event) toggles between Left Ear and Right Ear by setting the Left Solo state to 11 for Right and 10 for Left. The first '1' is the Solo state, and the second digit is the Swap state... '0' for normal (Left) and '1' for Swap (Right).

Btn1 (Ctrls=5 event) toggles the Both Ears state via GenDualL. If it is off, it also resets GenSoloL according to the current Btn0 state.

Btn2 (Ctrls=6 event) toggles the Setup state. It opens the Generator dialog and the Volume Control dialog, sets Stream Level controls to use dB instead of percent, sets Left Stream 0 to -30 dB, and toggles Amplitude Modulation (AM) on. It then shows the setup prompt message. Toggling Btn2 off restores Level to 0 dB (100%), toggles AM off, and removes the message.

Btn3 (Ctrls=7 event) controls noise type. It was set by the Phantom_Signals caller to be a multi-state pushbutton via Btn3="<M(3)", with values ranging from 0 to 3. The noise sources are Wave types 7-10, so the type is set via L.0.Wave=Btn3+7. Ctrl0 through Ctrl3 are disabled, then Btn3 is tested to determine which to enable, and which label to show on the button.




    Ctrl2="< " + UX


        Btn0="Right Ear"
        Btn0="Left Ear"


        Msg="Adjust volume for pulsing noise threshold.
Then toggle Setup off for 30 dB above threshold."


See also Auditory Phenomena and Experiments, Macro Examples and Mini-Apps


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