Just when I thought I couldn't be wrong, I was wrong. We have woodpeckers that drill into the arial telephone cables, and water seeps through the holes and partially grounds the tip and/or ring wires causing hum. I thought the hum/buz on my lines was a telco problem. The Qwest HQ noise team assures me that my lines are within spec. Sure enough, when I listen on the test set the lines are clear. The lines terminate at an Adtran 750 channel bank on my * system. When I reconnect the lines to the channel bank and make a call, I get the hum/buz noise. I have replaced every Adtran component (even the chassis), but the hum/buz stays with the lines. From the CO we have a digital fibre optic system which terminates at a neighborhood cabinet. From there, analog copper cables distribute service to the houses. I'm suspecting that the digital-to-analog process doesn't give a smooth analog signal but rather a "stair-stepped" signal, with each step 1/8000 sec in duration (I wish I had a 'scope to confirm this.) The human ear can't hear this stair-stepped signal, so it's ok for POTS use. However, when I put this stair-stepped signal to the channel bank, it converts it back into a digital signal. I'm thinking that, because it's not a smoothed signal, the analog-to-digital process injects hum and buz. Does _anyone_ have more information on this? In the meantime I've had an ISDN circuit installed so as to have digital all the way to the * box. However, I can't get the ASUSCOM ISDNLink card to work with ISDN4Linux :-( Cheers, Mike P.S. The woodpeckers are still eating my house. There is a nest is an exterior wall which is driving my cats nuts! -- Michael Welter Introspect Telephony Corp. Denver, Colorado +1 303 674 2575 mike@introspect.com www.introspect.com
Mike,> The Qwest HQ noise team assures me that my lines are within spec. Sure > enough, when I listen on the test set the lines are clear. > > The lines terminate at an Adtran 750 channel bank on my * system. When > I reconnect the lines to the channel bank and make a call, I get the > hum/buz noise. I have replaced every Adtran component (even the > chassis), but the hum/buz stays with the lines. > > From the CO we have a digital fibre optic system which terminates at a > neighborhood cabinet. From there, analog copper cables distribute > service to the houses. I'm suspecting that the digital-to-analog > process doesn't give a smooth analog signal but rather a "stair-stepped" > signal, with each step 1/8000 sec in duration (I wish I had a 'scope to > confirm this.) The human ear can't hear this stair-stepped signal, so > it's ok for POTS use. > > However, when I put this stair-stepped signal to the channel bank, it > converts it back into a digital signal. I'm thinking that, because it's > not a smoothed signal, the analog-to-digital process injects hum and > buz. Does _anyone_ have more information on this?As I've mentioned to you in previous posts, I use to work as a telephone engineer for 20+ years and did a lot of noise measurements, etc, over the years. Your stair-stepped signal issue is not the problem for sure. If you could put a scope on the line, you wouldn't see jagged edges at all, however you "might" see the real source of the problem. In order to do that, you'd have to use a dual-input oscilloscope that has the capabilities of displaying the difference between those two inputs (differential mode), and have an input sensitivity that would go down to something on the order of .1 volts/div or so. The Qwest folks would be doing about the equivalent as the scope, but with a noise meter that typically is filtered to look only at the 20hz to 4000hz range (or something like that). Those devices will generally go down to about -90 db or so, and they also look for imbalances betwee tip & ring (eg, water in the cable). The meter should be far more sensitive then the average person's ears. If they obtained those measurements from outside your house (and they may have disconnected the internal wiring to do that), then in all liklihood there is something inside your house causing the imbalance & noise. If they came inside the house with the meter and indicated things were within spec, then something is messed up in the Adtran/asterisk area or the physical connections to it.> In the meantime I've had an ISDN circuit installed so as to have digital > all the way to the * box. However, I can't get the ASUSCOM ISDNLink > card to work with ISDN4Linux :-(Don't know anything about this card. Rich
On Sat, Apr 10, 2004 at 08:39:53AM -0600, Michael Welter wrote:> However, when I put this stair-stepped signal to the channel bank, it > converts it back into a digital signal. I'm thinking that, because it's > not a smoothed signal, the analog-to-digital process injects hum and > buz. Does _anyone_ have more information on this?This doesn't sound like the way that sampling errors usually work. They definitely aren't usually so consistent. If it were a sampling error, you may be able to smooth the signal by placing a capacitor in parallel with the unit doing the sampling. Have you checked the ground on your channel bank? Ground loops generally can pick up buz from power sources in other audio setups. While I would think that a phone setup wouldn't have this sort of problem, it may be worth checking. Does the buz sound like 60hz noise? If so, I'd look for some sort of power-related problem. Good luck. -- Jayson
Some people have some really wacky ideas about how sampled systems work :-) Regards, Steve Michael Welter wrote:> Just when I thought I couldn't be wrong, I was wrong. We have > woodpeckers that drill into the arial telephone cables, and water > seeps through the holes and partially grounds the tip and/or ring > wires causing hum. I thought the hum/buz on my lines was a telco > problem. > > The Qwest HQ noise team assures me that my lines are within spec. > Sure enough, when I listen on the test set the lines are clear. > > The lines terminate at an Adtran 750 channel bank on my * system. > When I reconnect the lines to the channel bank and make a call, I get > the hum/buz noise. I have replaced every Adtran component (even the > chassis), but the hum/buz stays with the lines. > > From the CO we have a digital fibre optic system which terminates at a > neighborhood cabinet. From there, analog copper cables distribute > service to the houses. I'm suspecting that the digital-to-analog > process doesn't give a smooth analog signal but rather a > "stair-stepped" signal, with each step 1/8000 sec in duration (I wish > I had a 'scope to confirm this.) The human ear can't hear this > stair-stepped signal, so it's ok for POTS use. > > However, when I put this stair-stepped signal to the channel bank, it > converts it back into a digital signal. I'm thinking that, because > it's not a smoothed signal, the analog-to-digital process injects hum > and buz. Does _anyone_ have more information on this? > > In the meantime I've had an ISDN circuit installed so as to have > digital all the way to the * box. However, I can't get the ASUSCOM > ISDNLink card to work with ISDN4Linux :-( > > Cheers, > Mike > > P.S. The woodpeckers are still eating my house. There is a nest is > an exterior wall which is driving my cats nuts!
Hi Michael, I tried to reply to your prive e-mail, but it seems like your mail service blacklists the whole of Hong Kong. :-\ Regards, Steve Michael Welter wrote:> Just when I thought I couldn't be wrong, I was wrong. We have > woodpeckers that drill into the arial telephone cables, and water > seeps through the holes and partially grounds the tip and/or ring > wires causing hum. I thought the hum/buz on my lines was a telco > problem. > > The Qwest HQ noise team assures me that my lines are within spec. > Sure enough, when I listen on the test set the lines are clear. > > The lines terminate at an Adtran 750 channel bank on my * system. > When I reconnect the lines to the channel bank and make a call, I get > the hum/buz noise. I have replaced every Adtran component (even the > chassis), but the hum/buz stays with the lines. > > From the CO we have a digital fibre optic system which terminates at a > neighborhood cabinet. From there, analog copper cables distribute > service to the houses. I'm suspecting that the digital-to-analog > process doesn't give a smooth analog signal but rather a > "stair-stepped" signal, with each step 1/8000 sec in duration (I wish > I had a 'scope to confirm this.) The human ear can't hear this > stair-stepped signal, so it's ok for POTS use. > > However, when I put this stair-stepped signal to the channel bank, it > converts it back into a digital signal. I'm thinking that, because > it's not a smoothed signal, the analog-to-digital process injects hum > and buz. Does _anyone_ have more information on this? > > In the meantime I've had an ISDN circuit installed so as to have > digital all the way to the * box. However, I can't get the ASUSCOM > ISDNLink card to work with ISDN4Linux :-( > > Cheers, > Mike > > P.S. The woodpeckers are still eating my house. There is a nest is > an exterior wall which is driving my cats nuts! > > > >