"Tim Wescott" <tim@seemywebsite.com> wrote in message news:d9GdnXRD65_XcLjeRVn-vw@web-ster.com...> > Assuming that things haven't changed in the 15 years since I last worked on > them "Real" ISDN lines such as you might get installed at your house are known > as BRI (Basic Rate Iforgottherest). BRI consists of not one but two > 64kbit/sec channels for data and/or voice, and a 9600 bit/sec channel for > signaling. A BRI line would probably only get you 64kbit/sec, but it should > be solid. ADSL gives, if I'm not mistaken, much more bandwidth, at least on > the "downstream" end because the designers know a dirty picture has a lot more > bits than the little packet that requests it.I'm quite close to my local switch, so I get a very nice 3Mbs download and 768kbs upload from my $30/month Verizon ADSL. So that is much better than ISDN speeds and possibly cheaper. Others I know with DSL are not so fortunate, often obtaining half or less of those rates. The competition from the cable company has helped as well. ADSL around here used to be 1.5Mbs, but when cable started advertising 4Mbs, DSL countered by doubling their top speed. In reality, cable is shared among multiple users and may slow down if your neighbors are all using heavy bandwidth. However, DSL is a direct connection from me to the local switch, so should be more consistent. That is unless there are other similar bottlenecks upstream!
Why the low frequency limitation on POTS?
Started by ●September 9, 2005
Reply by ●September 13, 20052005-09-13
Reply by ●September 13, 20052005-09-13
Jon Harris wrote: ...> I've also seen 800 Hz listed as the "ideal" geometric mean > (http://www.smeter.net/daily-facts/10/fact18.php). This is pretty close to what > you would get for the 20-20k case (geometric mean = ~632 Hz), and would dictate > 32 Hz - 20 kHz. As a matter of practicality, there isn't much in music below 32 > Hz, few speakers can reproduce it anyway, and the ear rolls off pretty fast down > there. As a point of reference, the low "E" string, which is the lowest note of > both the orchestral double bass and most electric basses used in contemporary > music, has a frequency 41.2 Hz. So I wouldn't lose too much sleep over the last > half-octave or so!800 is OK. 1000 is cutting off your lows to please your preconceptions. When the bandpass filter is the listener's ears, the number doesn't apply. It's intended as a gizmo-design guide for people with more-or-less normal ears. It's intended for "naturalness", not intelligibility of speech. In the words of my boss, William Webster, "It's a suggestion, not an edict." Jerry -- Engineering is the art of making what you want from things you can get. �����������������������������������������������������������������������
Reply by ●September 16, 20052005-09-16
jharris wrote:> I'm curious to know why the 300 Hz low frequency limitation exists on POTS. > Since fundamentals of the male human voice can easily extend below this, > it would seem beneficial to accomodate low frequencies, at least down to > say 150 Hz. Is there some historical reason that the low frequencies are > limited?A speech signal has a lot of energy at the fundamental, but very little information content. Most of the intelligibility of a speech signal has to do with how well the formant frequencies are reproduced. Removing the lowest frequencies allows more of the available dynamic range to be devoted to the parts of the signal that contribute most to understanding what is being said. It's amazing how much research the Bell Labs folks devoted to these sorts of topics. -- Dave Tweed
Reply by ●September 16, 20052005-09-16
"David Tweed" <dtweed@acm.org> wrote in message news:432AB20A.9477F8@acm.org...> jharris wrote: >> I'm curious to know why the 300 Hz low frequency limitation exists on POTS. >> Since fundamentals of the male human voice can easily extend below this, >> it would seem beneficial to accomodate low frequencies, at least down to >> say 150 Hz. Is there some historical reason that the low frequencies are >> limited? > > A speech signal has a lot of energy at the fundamental, but very little > information content. Most of the intelligibility of a speech signal has > to do with how well the formant frequencies are reproduced. Removing the > lowest frequencies allows more of the available dynamic range to be devoted > to the parts of the signal that contribute most to understanding what is > being said. > > It's amazing how much research the Bell Labs folks devoted to these sorts > of topics.Great contribution, David. That makes a lot of sense. Does anyone know if the results of some of those Bell Labs studies are available, ideally on-line?
Reply by ●September 16, 20052005-09-16
Jon Harris wrote:> "David Tweed" <dtweed@acm.org> wrote in message news:432AB20A.9477F8@acm.org......>>It's amazing how much research the Bell Labs folks devoted to these sorts >>of topics. > > > Great contribution, David. That makes a lot of sense. Does anyone know if the > results of some of those Bell Labs studies are available, ideally on-line?A 300-Hz low end is pretty common ham and mobile coms practice, too. If you can't get hold of the relevant issues of the Bell Laboratories Journal, that might be another avenue worth exploring. Mil specs? Jerry -- Engineering is the art of making what you want from things you can get. �����������������������������������������������������������������������
