Some More Background Information

Microphones:

    Microphones are a type of transducer which means that they convert energy from one form to another.  Sound waves cause disturbances in the air (mechanical energy) and this causes the diaphragm in the microphone to vibrate.  This vibration is registered as an electrical current and this then becomes the audio signal that can be recorded by a computer or other instrumentation.  For this project, the type of microphone used is extremely important because of the sounds being recorded.  Mice communicate mainly in the ultrasonic range which is above human hearing (20KHz and above).  This project requires a microphone that could pick up frequencies between 20-120KHz in order to be able to record all of the noise that the mice make during their behavioral experiment.  It is also important that a microphone has a relatively "flat" frequency response.  If a microphone has a "flat" frequency response than it is capable of recording all frequencies equally, meaning that it is just as sensitive to a frequency at the lower end of its range (for example 25kHz) as it is to a frequency at the higher end of its range (100kHz).  The following is the frequency response of the microphone purchased for this project.

Figure 1: Frequency Response of Ultramic 250K

Ultrasonic Vocalizations:

    Ultrasonic vocalizations (also known as USV's) is the name given to the sounds that mice make while expressing emotion and communicating with each other.  Mice can speak (make noise) in the range of human hearing to about 70KHz.  This range can be affected if the mouse is affected by disorders that cause language deficiency (such as down syndrome).  USV's are often studied to compare how disordered and normal mice interact with one another.  Such behavioral tests can also be used to distinguish which medications help the symptoms of language impairment caused by disorders.  Below is some more information about research being done on USV's.

WAV Files:

The WAV file format was ideal for this project, in comparison to other formats such as MP3, because it stores the most data into a single file.  A WAV file works by savings “chunks” of data and uses the linear pulse code modulation (LCPM) format (see Figure 2).  LCPM works by saving streams of data as sequences of amplitude values recorded over a period of time.  All of the information saved in the LCPM format is saved on a linear scale, meaning that the specific values stored as data points are directly proportional to the amplitude.  WAV files also save data based on resolution, sample size, and byte order through the LCPM format.  While the WAV format was ideal for this project to collect the most data from the microphone while it is recording, it should be noted that the audio files taken during experimentation are much larger than other file formats.

Figure 2: WAVE File Format