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Author Topic: PSTN line gain  (Read 60266 times)
JeremyW
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« on: January 31, 2015, 06:18:15 am »

Hi,

My original thread was getting a bit long and off topic so here's a new question:

New OBi110 working well - call quality is excellent, however I need to tweak the call volume on the PSTN line. All incoming calls are on the British Telecom PSTN line and the only comment is that the volume of my voice is a little quiet (to the caller). Which setting would be appropriate for tweaking that up a little and, while I'm at it, the caller volume on the PSTN line as well (but not as much).

Thanks.
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ianobi
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« Reply #1 on: January 31, 2015, 07:50:19 am »

In Line Port > Port Settings you will find these two parameters:

ChannelTxGain
Gain in dB (-15 to 15) to apply to the signal transmit from the OBi to the PSTN company

ChannelRxGain
Gain in dB (-15 to 15) to apply to the signal received by the OBi from the PSTN company

Adjust carefully - a change of 3dB upwards or downwards will double or halve the perceived volume.

There are two similar settings in the Phone Port to adjust the volume sent to and from the telephone plugged into your OBi110. If the volume to and from your SIP callers seems ok, then it is most likely that the adjustment is needed on the Line Port to only affect PSTN calls.


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JeremyW
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« Reply #2 on: January 31, 2015, 08:12:14 am »

Many thanks. I'll give that a go.
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drgeoff
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« Reply #3 on: January 31, 2015, 03:00:51 pm »

Ensure you have the line impedance setting changed from the default US value of 600 ohms.  If you have loaded the UK xml file that should have done it.
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JeremyW
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« Reply #4 on: February 01, 2015, 05:13:55 am »

Ensure you have the line impedance setting changed from the default US value of 600 ohms.  If you have loaded the UK xml file that should have done it.

Yep. That's OK. I have the UK config. Thanks.
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JeremyW
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« Reply #5 on: February 03, 2015, 11:17:25 am »

OK. I went too far I think. Set ChannelTxGain on the Line port to +3 initially but on the basis of one comment from someone who's hearing isn't the best (my error of judgement) I upped it to +5.

Today my wife took an incoming call (PSTN) and complained that her own voice echoed. Could that be down to too much Tx gain? Assuming so and unless anyone has any better suggestions I've dropped it to +2. Not sure what increments are best to use.
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ianobi
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« Reply #6 on: February 04, 2015, 02:13:59 am »

I'm afraid this is mostly a question of making changes and trying them out. I recommend setting volumes using a corded "plug-in" phone, as cordless dect phones have their own volume settings and may add confusion.

Quote
Today my wife took an incoming call (PSTN) and complained that her own voice echoed. Could that be down to too much Tx gain?

Echo may be caused by too high TX gain and/or mismatched impedance between the OBi and the land line. Although there is a theoretical impedance value to set the for the OBi (in the UK config file), in real life line conditions vary somewhat and trying a few other impedance settings can sometimes help. That's a last resort, changing TX and RX gains are the first step.

If you do not wish to bother your friends too much you can call 0800 500005 and listen to boring internal BT news to test your receive volume. Testing transmit is more difficult. If you have a spare phone you can plug into a socket on the PSTN side of your OBi, then you can listen to someone speaking on the phone attached to the OBi and get a rough idea of volume going to line - pick up the phone on the PSTN side of the OBi after the call is established. To do this dial the BT test number 17070 and select option 2 "quiet line test". This will remove all other noises such as dial tone while you test.

dBs as a measure of volume work in a logarithmic way, not a straight scale. Upping the level by 3dB will double the volume. Best to try 1dB at a time.

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JeremyW
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Posts: 48


« Reply #7 on: February 04, 2015, 02:18:38 am »

Thanks for the wealth of info. I'll experiment...
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JeremyW
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Posts: 48


« Reply #8 on: February 04, 2015, 10:23:19 am »

I'm afraid this is mostly a question of making changes and trying them out. I recommend setting volumes using a corded "plug-in" phone, as cordless dect phones have their own volume settings and may add confusion.

Quote
Today my wife took an incoming call (PSTN) and complained that her own voice echoed. Could that be down to too much Tx gain?

Echo may be caused by too high TX gain and/or mismatched impedance between the OBi and the land line. Although there is a theoretical impedance value to set the for the OBi (in the UK config file), in real life line conditions vary somewhat and trying a few other impedance settings can sometimes help. That's a last resort, changing TX and RX gains are the first step.

If you do not wish to bother your friends too much you can call 0800 500005 and listen to boring internal BT news to test your receive volume. Testing transmit is more difficult. If you have a spare phone you can plug into a socket on the PSTN side of your OBi, then you can listen to someone speaking on the phone attached to the OBi and get a rough idea of volume going to line - pick up the phone on the PSTN side of the OBi after the call is established. To do this dial the BT test number 17070 and select option 2 "quiet line test". This will remove all other noises such as dial tone while you test.

dBs as a measure of volume work in a logarithmic way, not a straight scale. Upping the level by 3dB will double the volume. Best to try 1dB at a time.


Hmm.. I'm confusing myself. If I deliberately call out over the PSTN by using **8, volumes are OK - the other party is maybe a little quiet but I get no complaints about the volume of my voice. If they call in (always over the PSTN), the caller volume level is higher but I then get comments that I 'sound quiet'. Any more clues from that?
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WelshPaul
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« Reply #9 on: February 04, 2015, 10:40:31 am »

What exactly are the values of both the ChannelTxGain and ChannelRxGain parameters under both the phone and line port configs?

If it was me I would setup a Voipfone account on an empty SPx slot and perform an echo test by dialing 152 - When you speak into the handset anything you say is played back to you! Adjust the phone port ChannelTxGain and ChannelRxGain until you get the desirved volume levels. (Use a corded telephone)

Now remove the Voipfone account if no longer required. Next thing is to dial out over the PSTN line, any old freephone number will do and listen any recorded messag or IVR - Adjust the ChannelRxGain under line port if needed until you have a comfortable level of volume.

All that's left to do know is adjust the ChannelTxGain under line port, increase it in steps of one until people stop saying you sound quiet.
« Last Edit: February 04, 2015, 11:01:05 am by WelshPaul » Logged

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ianobi
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« Reply #10 on: February 04, 2015, 11:13:49 am »

I believe Jeremy has a sip provider on sp1. I suggest setting up a speed dial like so:
sp1(thetestcall@sip2sip.info)

This provides many tests including an echo test. The female voice likes to explain the tests, so you can listen and adjust received volumes accordingly. Also record and play back messages can be useful. It's free and can be accessed without an account at sip2sip.info.

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WelshPaul
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« Reply #11 on: February 04, 2015, 11:21:07 am »

I believe Jeremy has a sip provider on sp1. I suggest setting up a speed dial like so:
sp1(thetestcall@sip2sip.info)

This provides many tests including an echo test. The female voice likes to explain the tests, so you can listen and adjust received volumes accordingly. Also record and play back messages can be useful. It's free and can be accessed without an account at sip2sip.info.


Hey thanks... This will come in handy! Smiley
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ianobi
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« Reply #12 on: February 04, 2015, 11:35:20 am »

Paul - I know you have an OBi1032. Try 3333@sip2sip.info - it should connect using G722 and sounds quite good over the speaker   Smiley
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WelshPaul
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« Reply #13 on: February 04, 2015, 12:13:49 pm »

I actually use G722 for my main calls, I have a raspberry pi running raspbx. Voicehost.co.uk support the G722 codec and they are my primary ITSPA. Grin

I ordered the new raspberry pi 2 B board to replace my B+ and hopefully it will be here to tomorrow.  Wink

I was testing HD call qaulity today between my yealink T48G (Replaces my Snom 870) and my OBi1032... It's a nerds wet dream!  Cheesy

I will try out 3333@sip2sip.info in the morning.  Tongue
« Last Edit: February 04, 2015, 12:15:24 pm by WelshPaul » Logged

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JeremyW
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Posts: 48


« Reply #14 on: February 04, 2015, 12:47:41 pm »

I believe Jeremy has a sip provider on sp1. I suggest setting up a speed dial like so:
sp1(thetestcall@sip2sip.info)

This provides many tests including an echo test. The female voice likes to explain the tests, so you can listen and adjust received volumes accordingly. Also record and play back messages can be useful. It's free and can be accessed without an account at sip2sip.info.


Hey thanks... This will come in handy! Smiley

I have no problems with SIP calls though. Will this help?

In answer to your question about levels Paul - see attached shots.


* Phone Port.png (26.28 KB, 770x302 - viewed 963 times.)

* Line Port.png (28.49 KB, 767x324 - viewed 971 times.)
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WelshPaul
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« Reply #15 on: February 04, 2015, 01:11:36 pm »

Try setting the -2 and -1 values both to 0

Regarding the line port Tx set it to 0

Test again.
« Last Edit: February 04, 2015, 01:14:31 pm by WelshPaul » Logged

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JeremyW
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Posts: 48


« Reply #16 on: February 04, 2015, 04:11:40 pm »

Try setting the -2 and -1 values both to 0

Regarding the line port Tx set it to 0

Test again.

Done that. I'll test on a few calls tomorrow and report back.
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JeremyW
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Posts: 48


« Reply #17 on: February 12, 2015, 03:26:54 am »

Try setting the -2 and -1 values both to 0

Regarding the line port Tx set it to 0

Test again.

Nothing I've tried really seems to work. Tweaking the TX gain up on the Line port just resulted in echo and the latest tweak above didn't seem to have any effect. Any further thoughts on something I else I can try?

Thanks.
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JeremyW
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Posts: 48


« Reply #18 on: February 12, 2015, 12:50:45 pm »

Extensive testing this evening: All TX and RX settings at default, then tweaked the Line port TX up to 2 from the default (0). Volume of my voice to the caller was improved but at the beginning of the call there was a slight amount of echo, which settled down, and then a slight delay causing us to talk over each other slightly. Manageable but I'm wondering if any further tweaks are possible to iron out the wrinkles or if I just have to accept the imperfections.

EDIT: These are PSTN calls ONLY. SIP calls are fine (they are only outgoing, I have no incoming SIP).
« Last Edit: February 12, 2015, 12:52:46 pm by JeremyW » Logged
drgeoff
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« Reply #19 on: February 12, 2015, 03:40:53 pm »

SIP will always have an advantage over PSTN/POTS regarding echo and consistency of levels.

When you use POTS the analogue audio signals to and from your handset are on a common pair of wires.  In your OBi they are separated and amplified or attenuated according to the level settings that you have been tweaking.  Then the two signals have to be again on a single pair of wires to travel to/from your telco's switch.  There they are separated again for carriage over the digital trunk network.

Those separation and joinings are never perfect; there is always some leakage of one direction into the other.  Some of the imperfection is caused by the non-ideal characteristics of the 2-wire/4-wire conversion circuits and some is due to the actual line impedance being different from the value assumed in the design of the 2-wire/4-wire converter. Those leakages manifest themselves as echo.

In the majority of cases the end result is not troublesome but there may well be some, possibly yours, where there are enough significant shortcomings that their combined effect is troublesome.
« Last Edit: February 12, 2015, 04:32:28 pm by drgeoff » Logged
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