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XTS5000 - problem in securenet voice quality
Posted: Thu Mar 17, 2005 12:00 pm
by radio-link
Hi out there!
Today I had two XTS5000 on the bench, and the user complained that on some conventional channels securenet operation (DES-XL) gives better voice quality than on others. Not believing it, I played around and found out that there are personalities with and others without pre/deeemphasis; the difference is immense! As far as I know the inner working of securenet, after all it is a digital mode with some kind of FSK transmission, so how the h*** could analogue filtering occur and influence the voice quality? Is it a bug, or is it feature? Due to the config of the whole network it is not possible just to change from "without" to "with" pre/deemphasis, so it looks that the customer has to live with the degraded quality with plain FM?!
Posted: Thu Mar 17, 2005 3:30 pm
by wavetar
The pre / de-emphasis is applied to the analog signal, both before & after the IMBE conversion, so it would have a significant effect on the audio, regardless of what modulation you are using.
Todd
Posted: Sun Mar 20, 2005 11:53 am
by radio-link
wavetar wrote:The pre / de-emphasis is applied to the analog signal, both before & after the IMBE conversion, so it would have a significant effect on the audio, regardless of what modulation you are using.
Todd
The funny thing is, in APCO mode (with IMBE vocoder) nothing can be observed, no difference at all, just in DES-XL the effect occurs.
Posted: Sun Mar 20, 2005 12:24 pm
by mancow
That's because in "Apco" mode it's all digital. The filter issues you mention aren't a factor since they aren't used. The vocoder takes care of it.
mancow
Posted: Mon Mar 21, 2005 12:25 am
by radio-link
mancow wrote:That's because in "Apco" mode it's all digital. The filter issues you mention aren't a factor since they aren't used. The vocoder takes care of it.
mancow
Yes, of course; but in securenet mode also everything is digital (just another codec and bitrate), so I do not see there any difference how the signal should be treated.
I fear that more such complaints are to come; here in germany especially authorities tend to use FM without pre/deemphasis, so they will suffer from really shitty audio when using des-xl.
Posted: Mon Mar 21, 2005 12:01 pm
by wavetar
Look at it this way. With IMBE digital, you have somewhere in the area of 90-95% audio fidelity recovery of the original analog signal. With Securenet, you only get about 65-70% recovery. A little difference (pre/de-emphasis) in the analog audio can mean a big difference in the audio fidelity recovery for Securenet.
Todd
Posted: Tue Mar 22, 2005 10:17 am
by radio-link
wavetar wrote:Look at it this way. With IMBE digital, you have somewhere in the area of 90-95% audio fidelity recovery of the original analog signal. With Securenet, you only get about 65-70% recovery. A little difference (pre/de-emphasis) in the analog audio can mean a big difference in the audio fidelity recovery for Securenet.
Todd
Yes, it seems so. But why does Mot not use the audio filtering which gives the best audio automatically? Why does the radio use "FM plain" like in normal operation, while pre/deemphasis in the audio path would improve things a lot and does not change a thing on the RF path, due to the digital nature of the signal?!
Due to codeplug space it is not possible to store several hundred channels twice, once in plain FM for clear operation, and once agin with pre/deemphasis just for DES-XL.
I really dislike this...