Most current (if not all) digital voice recorders have quit a long
range so recording a teacher at 15 feet away won't be a problem.
Digital recorders with range settings are not common simply because
there is little a recorder can do about the perception of range: a
recorder simply records what it's microphone receives and it's
practically impossible to tell the microphone to concentrate on a
certain voice or something.
This means that, when you want to record a person which is some
distant away from the recorder, that there needs to be little or no
surrounding sounds. So if all your classmates are yelling at each
other, you won't be able to record your teacher in a proper way.
Settings on a voice recorder can do little or nothing about this.
On the other hand, if the person you are recording is close to the
microphone (as with an interview) surrounding sounds will be much less
of a problem. This is because the voice of the person being
interviewed is a lot closer to the microphone than other sources and
will therefore always stand out.
To sum it up: good quality voice recorders will have no problem with
recording a voice a distant away (as long as there are little
surrounding sounds) and will have no problem recording a voice close
by. No settings can or need to be changed (except for maybe the volume
when playing back the recording).
Now, some good quality digital recorders I came accross. All of the
following recorders can record at least 90 minutes.
In my experience, Panasonic and especially Olympus are the best brands
in this area, therefore I will give you their products.
-Olympus Voice-Trek V-10 Digital Voice Recorder
This recorder is one of the few which does have a setting which can
influence the direction of the microphone. This is helpfull if you
want to concentrate on a person which is in front of recorder (for
More information can be found here:
-Olympus Digital Voice Recorder, Model VN900
This recorder is pretty basic but still has a good quality. Price is
More information: http://www.abtelectronics.com/scripts/site/site_product.php3?id=8352&AID=164318&PID=34758&setflag=1023393021
You can but it here:
-Panasonic RR-US321 IC Digital Voice Recorder
A good recorder. Mid-range, mid-price. Can record 105 minutes.
You can buy it here:
-Olympus DS-320 Digital Voice Recorder
Really popular this one. Has a long recording time and has the ability
to automatically convert recordings into Word documents. Price is
quite high though.
You can buy it here:
I hope this answer is to your satisfaction, if you have any further
questions, don't hesitate to ask for a clarification.