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  Topic: Audio queries... (3 replies)
#1     Sat Jul 07, 2007 4:02 am
GW3VVC
Island of Anglesey
 
Join Date: Jul 2007
Posts: 2
Subject: Audio queries...

Hi,

Just evaluating CQ100 and have a couple of questions/comments which someone might be able to help me with.

Firstly the audio quality - I've never done any voip before so I've no idea what the quality of the audio should be - it sounds very much like the usual telephone quality - not very good but readable - I did read somewhere that the maximum bandwidth used is 1.8 khz - as I presume the signals are digital rather than analogue I'm not too sure how this should affect the quality.

Also the speech breaks up - this appears to be worse with some stations than others - but appears to happen on pretty well every signal - I have ensured that I don't have anything else running - I've even briefly turned off my firewall - but it really makes no difference.

I have tried cw contacts using CQ100 and when the signal breaks up this can obviously make copying more difficult - however - and here I would really wellcome some feedback from experienced cw ops here on CQ100 - as the signal is sent in packets and presumably some packets have to be repeated - what effect does this have on the received copy ? I do sometimes as I mentioned have difficulty copying portions of the cw and I suspect it's not just because some of the cw has 'fallen into a hole' - presumably lost packets are being repeated - and maybe introducing a short delay between characters - this presumably happens so quickly that I would not have thought the effect would be noticeable - just ocassionally something about the cw sounds odd...

Sorry that last para sounds a bit garbled - maybe some cw ops out there may understand what I'm saying...

PC here is a modern Dell Dimension 9150 - 3Ghz with 2 Ghz RAM. I am at present using the on-board sound but have a Creative pci card sound card which I may try later.

If the above sounds negative - it's not meant to be - I like CQ100 and will probably stay with it after the trial period - but I would like to know what to expect...

Couple of other queries but I'll leave them 'till later - don't want you good people falling asleep !!!

Regards,

John
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#2     Sat Jul 07, 2007 7:39 am
VE3EFC
 
Join Date: Aug 2006
Posts: 724
Subject:

Hi John. The audio bandwidth is monophonic, 8,000 samples per second with each sample at 2 bytes. According to Nyquist, this sampling will gives a top end about 4 kHZ. This data is compressed to 1.65 kilobytes per second using the GSM 6.10 codec. When you add in packet headers and control commands, the CQ100 system requires about 1.8 kilobytes per second. GSM 6.10 is a lossy compression which is optimized for voice. It does reduce the quality of the original sampling.

I seldom hear any breakup on my office DSL or my home cable, so if you are hearing it on everyone, I suspect the problem is at your end.

The CQ100 transceiver has an anti-jitter buffer where the playback of incoming audio is delayed slightly in order to have data available to fill in any gaps, but there is a limit on this delay.

Here is some help about breakup...
http://www.qsonet.com/qbb/viewtopic.php?t=52
http://www.qsonet.com/qbb/viewtopic.php?t=652

Are you using Tiscali?
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#3     Sat Jul 07, 2007 9:53 am
GW3VVC
Island of Anglesey
 
Join Date: Jul 2007
Posts: 2
Subject:

Hello Doug,

Thanks for the quick reply - I appreciate it...

> GSM 6.10 is a lossy compression which is optimized for voice. It does reduce the quality of the original sampling.

Maybe I've been expecting HiFi and that's not realistic nor really a requirement - I must say I've heard a number of stations with really nice audio but all the signals do have that compressed characteristic - I have no problem with that - I was merely wondering exactly what I could expect from the system.

> I seldom hear any breakup on my office DSL or my home cable, so if you are hearing it on everyone, I suspect the problem is at your end.

I'll need to examine this again. My PC is quite quick - an Intel 3.00Ghz duo core but I am using the on-board sound. I do have a Creative GeForce sound card but removed this when I was trying to locate a BSOD problem a while back. Now that I have that sorted I may re-install the GeForce and see if that has any effect on the sound break up.

> Are you using Tiscali?

No, I'm using a local ISP (Gaya Technologies) who provides 'net access via wireless. The AP is local to me and my Cisco 350 wireless card software indicates good signal strength. I can download large files quickly so I have a good link.

I've tried ensuring no other software is running, even disabling my virus checker and firewall momentarily but the audio still breaks up...maybe I happened across some stations yesterday who had rather poor links to the 'net - today it does sound better but I will reinstall the Creative anyway.

Thanks again for the quick reply and your suggestions Doug. I've a feeling that I may use CQ100 quite a lot - especially with the state of the hf bands at the moment...

73's de John
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#4     Sun Jul 15, 2007 1:22 pm
W7RJR
Spokane, WA
 
Join Date: Oct 2006
Posts: 114
Subject:


GW3VVC wrote:
I'll need to examine this again. My PC is quite quick - an Intel 3.00Ghz duo core but I am using the on-board sound. I do have a Creative GeForce sound card but removed this when I was trying to locate a BSOD problem a while back. Now that I have that sorted I may re-install the GeForce and see if that has any effect on the sound break up.

> Are you using Tiscali?

No, I'm using a local ISP (Gaya Technologies) who provides 'net access via wireless. The AP is local to me and my Cisco 350 wireless card software indicates good signal strength. I can download large files quickly so I have a good link.

I've tried ensuring no other software is running, even disabling my virus checker and firewall momentarily but the audio still breaks up...maybe I happened across some stations yesterday who had rather poor links to the 'net - today it does sound better but I will reinstall the Creative anyway.


73's de John


John

You may be experiencing 'dropout'. This is characterized by the audio stream disappearing anywhere from 1 to 30 seconds. Sometimes the callsign display will clear. When the audio returns there may or may not be missing information. At times you may have to switch to another band and then return (connection was lost).

Don't be too quick to blame this on your computer or internet connection!

This problem might be minimized by disabling all background processes that are 'internet enabled'. If you download a packet analyzer you can examine the data stream and see what is happening. I use one called 'wireshark' and is a free download, just google it. Start a capture session with CQ100 running. When a breakup occurs note the 'time elapsed' displayed in the analyzer. Stop the capture and scroll through the entries until you find the 'time' you noted. Note any errors you find or processes running at that time.

This, I believe is the only way to tell what is going on with your particular installation. Good luck. Post here if you need more help.


73
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