Mike Rivers wrote:
In article writes:
Is there any digital recorder, (and by that I mean anyone that records
on a hard disk or RAM memory which could be then loaded on a PC),
which can record continuosly for 2 weeks - non stop?
All operating systems have some limit to maximum file size. I suppose
the first think to look at is how low could you go in quality. If you
record at a low sample rate and low resolution, then compress on the
fly, you might be able to squeeze two weeks worth of recording into
something that an operating system could handle.
Many filesystems these days use 64-bit files. A 32-bit file can be
2 GB in size, so a 64-bit one can be about 4 billion times as big as
that, in other words about 8 million terabytes. That should be enough
space to record 32 channels of 192 kHz 24-bit for about 31,700 years.
But I don't have the
knowledge or patience to run the numbers. Arny probably does. How bad
would it have to be in order to fit a say 170 hours of recording into
a gigabyte?
It would be pretty darned bad. That's 1,209,600 seconds, and a gigabyte
is about a billion, so it leaves just under one kilobyte to record a
second's worth of audio. So, you can record 1 kHz sampling rate with
8 bit samples, 2 kHz sample rate with 4 bit samples, etc., etc.
However, I've heard stuff recorded with 56 kilobit/s MP3 at 22050 Hz,
and it wasn't atrociously bad. So 56 kilobit is only 7 kilobytes
per second, which is about one order of magnitude worse than you'd
need to fit in one gigabyte.
But, that means you should be able to fit it in 10 gigabytes if you
want relatively low quality. If you go up to 128 kilobit/s MP3, you're
still only talking about around 20 GB of storage.
So, this is something that could easily be done by a computer. All
you'd need to do is compress on the fly. That'll probably require
a relatively fast processor, but the software does exist. You could
use, for instance, Linux or Unix with lame to do the encoding and some
command line program (audiorecord on Solaris) to do the recording.
Come to think of it, though, I'm not sure if the MP3 format itself
can support files bigger than 2 GB. So, you might have to break it
up, but that's not a big deal. If you were going the command-line
Unix route, you could do something like this to automatically
break it up into 500 MB increments:
seqnum=1
audiorecord -c 1 -s 44100 -e linear |
while true
do
dd ibs=512 count=1000000 of="$seqnum".raw
touch "$sequnum".raw.done
seqnum=`expr "$seqnum" + 1`
done
Then all you've got to do is have an MP3 encoder, like LAME
for instance, come along behind that and encode every .raw
file once it sees the corresponding .raw.done file has been
created.
So, it's kind of ugly and not user-friendly, but it certainly
can be done.
- Logan