Re: Enhanced hearing


"PPP" <pispaspos@xxxxxxxxx> wrote in message
news:1162235108.517536.98140@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
Good morning!

I'm trying to make an enhanced hearing circuit (kinda like Superman).
For my conceptual design, I read some of the tips I've gathered from
various postings in this group and also from various readings. So far,
I've come up with a crude concept:

- Audio input coming from a small microphone (electret-type?)
- Output from microphone is AC coupled to a voltage follower / buffer
audio op amp
- Audio op amp buffer is single supply so i will need a virtual ground
in one of the input pins that will be approximately 1/2 of the supply
voltage
- From the two steps above, I'm assuming that I won't have any control
of the DC level bias from the microphone output

- My buffered signal would then be split two ways... i'm assuming i can
just connect the buffered output to two different op amp inputs... part
of the signal will be sent to a level detector and the other part would
be the actual hearing enhancement gain op amp


- The level detector part would probably consist of an active rectifier
with a unity gain with its output being sent to a comparator.... the
output of this comparator would somehow interface to the gain op amp so
I can adjust the gain if the audio level input is too high... i saw an
active rectifier circuit in the Arts of Electronics book, so I think I
can use that one.

- The gain part would consist of an audio op amp with a variable
resistor for gain adjustment... but then this is where I get stuck. For
the gain section, I do not know how I can amplify my audio signal
without amplifying the DC component.

Since I do not have that much experience in electronic design compared
to others here, I was hoping maybe you, the experienced ones, can help
me answer the following questions:

1). How can I amplify an audio signal correctly without clipping the
output if I use a single-supply configuration?

2). How can I interface the level detection portion with the gain
portion? (I was thinking maybe I can use some sort of "voltage
controlled resistor" if there is one as part of my gain feedback
scheme).

3). What parameters would dominate my choice of parts for this type of
application? (I'd like this to be battery powered, so I'm assuming I
need some sort of low voltage, low power op amps. But I do not know how
to spec out the microphone and headphones for battery applications.)

4). How many questions can I ask before you guys/gals get sick of me?

Thanks!

If you want to do something more advanced than simple analog circuits,
parabolic reflectors and the like to enhance sound, consider using DSP,
Digital Signal Processing to accomplish your goals. One thing you could do
with DSP is frequency shift so that you can hear bats and ultrasonic insects
and other interesting things either above or below the frequency range of
human hearing. Another thing is to selectively amplify only certian
frequencies or certain sound patterns to increase the aural acuity. Still
another is noise shaping and filtering to increase the signal to noise
ratio. Furthermore it is possible to do correleation techniques on very weak
repetitive signals to pull them out of noise. There's many other neat things
that can be done with DSP. If this is for a class or to learn somethng more
or less at the state of the art, I suggest you look into it.
Bob


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