Hearing Science - Audio Signals & Devices

There are times when the acoustic signal needs to be stored for use at different times or transmitted over distances larger than the distance the original wave could travel. How is the acoustic signal modified at this point?

How the signal will be stored, how it will be transmitted, and how it will be reproduced at a later time.

Converting Acoustic signal into an electrical signal. (audio signal)

What is an audio signal?

An electric waveform having frequencies within the acoustic range that is audible to humans.

How can the audio signal be stored?

• Electric (most common, computer files, mp4s)

• Optic (dvds or cds)

• Magnetic (caset tape)

• Mechanic (outdated, vinyl record)

What is the most common feature for all audio signal to be recorded and reproduced? 

They need some form of electricity to be recorded or reproduced.

Define Transducer (for transmission):

Devices that convert one form of energy to another.

What device converts acoustic energy into elecrtric energy?

Audio transducer or an electroacoustic transducer. 

Define Electroacoustics:

The area of hearing science concerned with the conversion of acoustic energy into electric energy and the processing and transmission of these audio signals. 

How is acoustic energy converted into electrical energy?

Receivers convert acoustic signal (or the input) into electrical energy (microphone).

Transmitters (microphone) will convert electric energy back into acoustic energy for transmission

What are the two general types of audio transducers?

Receivers and Transmitters

How do receivers work?

Converting acoustic signal (or the input) into electrical energy.

What are the two different types of microphones?

Pressure and Gradiant.

Define Pressure Microphone:

In response to sound, a thin membrane (diaphragm) moves in response to changes in sound pressure at the front of its surface. Sound waves are coming directly at teh diaphragm, causing it to vibrate.

Also referred to as Omni-Directional Microphones.

Define Gradient Microphone:

In response to sound, it moves between the sound wave arriving at the front of the microphone and the back of the microphone. 

Also referred to as Directional Microphones. 

What’s the difference between Directional and Omni-Directional Microphones? 

Directional microphone moves in response to sound differs depending on where the sound is coming from. 

Omni-Directional microphone moves in response to sound are the same regardless of the direction of the sound. 

How do transmitters work?

Converts electric energy back into acoustic energy for transmission.

What are nonreciprocal transducers? Provice an example/

Tranducer that can only take in input. 

A sound bar on your tv. A microphone that a signer uses to sing into.

Waht are reciproal transducers? Provide an example.

Tranducer that can only recieve input and produce output.

A cell phone.

Most digital hearing aids employ ____ types of microphones and parameters can be set, which allow the hearing aid user to ______ ____ ___ _____ _______ microphone settings depending on listening situation.

(Bob! Stop Beating Anne’s Feather Box!) 

Both ; Switch Back And Forth Between

Under what listening situation would an omni-directional microphone be used?

In situations where the subject doesn’t need to eliminate any noise around their head because it’s quiet. The subject and another person are trying to have a conversation. This microphone picks up sounds 360* around their head.

Under what listening situation would a directional microphone be used?

In situations where the subject needs to eliminate any noise around them to hone in on a specific signal. The hearing aids minimize the surrounding noise.

Name the number of technical parameters that characterize the operation of microphones: 

• To quantify and describe the microphone’s performance and physical limits.

• Establish how strong an electrical signal is produced relative to the sound input

• Limit the amount of sound that the microphone can handle.

• To establish a total range of sound levels that it can handle effectively.

Tell us what sounds the microphone can successfully hear, how loud those sounds can be, and how accurately it will reproduce them.

What are microphones sensitive to and need to be protected from?

The sound input (sound pressure)

Why do technical paramters character the operation of loudspeakers?

To quanitify ability to convert electrical signal back into acoustic energy and to define operational limits.

Loudspeakers of different sizes reproduce different _________ ranges.

Frequency

Difficult for one loudspeaker to produce loud low- and high-frequency sounds due to membrane parameters; thus, many loudspeakers of different sizes reproduce different frequency ranges, such as:

Bass 

Whereas loudspeakers emit the output audio signal to the environment, where do earphones emit the signal? 

Directly to the human ear.

What do earphones serve to eliminate?

Eliminate potential background noise.

Define the two basic types of earphones:

Over the Ear Headphones: Aural headphones, cover or rest on the pinna.

In the Ear Headphones: Inserted into the pinna, exanding in the ear canal, providing sound dampening. 

Once the acoustic signal is converted, it is processed and transmitted by the electronic components along what? 

Electroacoustic chain

What modifies audio signals and eliminates noise and crosstalk that may interfere with the transmission of the desired signal? 

Signal Processors.

Why do most audio signals need to be amplified before being transmitted to the environment or the ear (in the case of hearing aids)? 

Those who need hearing aids, with hearing loss, need a louder sound. So, one needs to amplify that sound along the electroacoustic chain. 

Define Amplifier:

A device that increases the voltage (power) of the audio signal.