Masking--Effects of Frequency



Imagine you are listening to the radio and the phone rings.  How loud should the ringer be for you to hear it? 


Masking occurs when one sound prevents you from hearing a second sound. Volume, measured in decibels (dB), would clearly affect how easily you could hear either sound.  Do the relative pitches of the two sounds matter?  To ask this question, you would need to vary both the pitch and the volume of the second tone.  The graph to the right shows hypothetical data from such an experiment.  The first tone, or mask, was presented with a second tone that was either higher or lower in frequency, at a range of different volumes, all softer than the mask.  The softest tone was 36 dB's quieter.  If only volume matters, you would expect to perceive two tones at a particular dB for all frequencies, as shown.  Is this truly the case? To examine this, participate in the following task.  Will your perception depend only on volume, or will pitch matter?



Adjusting your volume...

Adjust the volume of your RealPlayer console or computer speakers until you can just detect this >low, soft tone.



Taking the test...

Listen to the trials as many times as you like, and then check whether you hear one or two tones.  When you are comfortable with the task, feel free to listen only once to each trial.  After you complete the set, press the "Register" button beside the table to view your results.  Don't worry about saying "one" or "two" an equal number of times, just mark whether or you not you hear one or two tones.  Once you have completed the task, graph your results.


One tone or two?

















>Trial #1


>Trial #9


>Trial #17



>Trial #2


>Trial #10


>Trial #18



>Trial #3


>Trial #11


>Trial #19

    your data...              


>Trial #4

>Trial #12


>Trial #20


Tone 2 (Hz)

-36 dB

-27 dB

-18 dB

-9 dB


>Trial #5


>Trial #13


>Trial #21



>Trial #6


>Trial #14


>Trial #22


>Trial #7


>Trial #15


>Trial #23


>Trial #8


>Trial #16


>Trial #24






Catch trials, percent correct 





Results & Discussion

To graph your responses, you will need to copy and paste each column into the graphing program of your choice.  The mask, or primary tone was concert A, 440 Hz, and the secondary tones (Tone 2 in the table) were various E's--two below the A (165 Hz and 330 Hz) and two above (660 Hz and 1320 Hz).  The dB levels of the second tone were always softer than the primary tone, ranging from -9 dB to -36 dB. The first column contains the frequency of the second tone (in Hz), with a column for each decibel level which records whether you thought you heard one or two tones when in fact two tones were presented.