First time listening to DMR voice via a local repeater. The voices sound either compressed, or pitch shifted slightly lower...Sometimes it seems like the speaker is slurring words or drunk a bit. The high end of voices seems gone. Do typical DMR repeaters use compression for efficiency? If so are there typically settings that can be changed for this? Any other explanation for this?
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Do repeaters use compression?
- Thread starter bobcrean
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slicerwizard
Member
Of course digital voice uses "compression". DMR's AMBE+2 implementation uses only 2450 bits per second to convey voice. However, it has nothing to to with repeaters.
6.25 kHz of bandwidth does not convey the human voice as well as analog with more bandwidth. Additionally, some inexpensive DMR radios have poor transmit audio which makes it more difficult to understand. The best sounding DMR radio I have ever heard is a Kenwood 5300 series. It costs around $1000, or was it $3000, I forget.
1. Yes, digital modes, DMR being one of them, typically use less bandwidth for efficiency and or to also pass data with the audio.
2. The settings that can be changed would be to use a different digital mode that sounds better to you. I prefer P25 and Yaesu Fusion (C4FM).
3. All DMR repeaters are not the same, nor is the ancillary equipment installed with it. Additionally, the skillset of the installers is not the same.
Another way to fix it is for everyone to avoid using inexpensive DMR radios, or avoid talking to someone until they purchase a better radio. These two probably will not happen. Around here DMR was very popular a few years ago. Now it is very quiet. Of all the DMR repeaters near me, I only hear traffic about twice a week. (In other places it could be quite busy)
1. Yes, digital modes, DMR being one of them, typically use less bandwidth for efficiency and or to also pass data with the audio.
2. The settings that can be changed would be to use a different digital mode that sounds better to you. I prefer P25 and Yaesu Fusion (C4FM).
3. All DMR repeaters are not the same, nor is the ancillary equipment installed with it. Additionally, the skillset of the installers is not the same.
Another way to fix it is for everyone to avoid using inexpensive DMR radios, or avoid talking to someone until they purchase a better radio. These two probably will not happen. Around here DMR was very popular a few years ago. Now it is very quiet. Of all the DMR repeaters near me, I only hear traffic about twice a week. (In other places it could be quite busy)
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Ubbe
Member
If you speak too close to a microphone or use compression you loose high end and add low end frequencies in the voice band. All good compressors have some sort of bass cut and/or high end increase to compensate for that problem.
Also if the data bits are lost during the air transmission it will create errors in the data and will also reduce the signal to a low defined audio signal without any high end and syllables will be lost.
DMR mostly uses 2 timeslots at a 12,5KHz bandwidth and Tetra uses 4 timeslots at a 25KHz bandwidth but the audio quality in Tetra are much better. But the equipment also costs 10 times more. Both hardware and software are probably then more advanced in Tetra equipment.
I've heard DMR transmissions that sounds real good but the exact same people could later sound awful, so DMR are probably more demanding of the correct microphone technique. Generally analog radio are much more forgiving of incorrect use of microphone gain and usage than digital radio as the dynamic range of the audio are very limited in most digital radio systems that requires a perfectly balanced audio level from a microphones compressor/limiter circuit.
/Ubbe
Also if the data bits are lost during the air transmission it will create errors in the data and will also reduce the signal to a low defined audio signal without any high end and syllables will be lost.
DMR mostly uses 2 timeslots at a 12,5KHz bandwidth and Tetra uses 4 timeslots at a 25KHz bandwidth but the audio quality in Tetra are much better. But the equipment also costs 10 times more. Both hardware and software are probably then more advanced in Tetra equipment.
I've heard DMR transmissions that sounds real good but the exact same people could later sound awful, so DMR are probably more demanding of the correct microphone technique. Generally analog radio are much more forgiving of incorrect use of microphone gain and usage than digital radio as the dynamic range of the audio are very limited in most digital radio systems that requires a perfectly balanced audio level from a microphones compressor/limiter circuit.
/Ubbe
MTS2000des
5B2_BEE00 Czar
The quality of the radio's DSP and audio make the difference between good audio and utter garbage. This is true with DMR, P25, NXDN, TETRA and anything that uses a vocoder. Piss poor DSP/firmware, piss poor audio. Old, ancient subscribers with early versions can sound horrible where as current releases resolve issues. So does how the subscriber is programmed plays a factor in the delivered audio quality.
WA0CBW
Member
If it is a commercial repeater in the VHF or UHF band (part 90) it must be narrowband 12.5 KHz. There are a few exceptions where 25KHz is allowed.
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slicerwizard
Member
25 kHz DMR? No such beast that I'm aware of.
Or it could be working perfectly and this scanner user isn't familiar with the way digital voice sounds? It does sound quite different compared to analog.
Perhaps like the many customers who thought "going digital" was going to CD-quality audio from cassette tapes...?
Perhaps like the many customers who thought "going digital" was going to CD-quality audio from cassette tapes...?
lu81fitter
Member
User etiquette is a real problem. I have heard one side of a conversation on a DMR system that is perfect. When the response comes back, it is barely intelligible. It sounds like they have the mic in their mouth. I notice this on the same system with different users. Most notably, the dispatch, where you know they are using the same radio. Some sound really good, others terrible.
I think lu81fitter has it. I've noticed the same thing. Some users sound perfectly clear and nearly like themselves (in real person or on analog); others, not so much. Most of the users use the Motorola lapel speaker-mic's. I'll observe how those that sound good use their mic's.
R8000 says the repeater just passes the 1's and 0's on; I'm more than happy to talk to the repeater's owner about how it was set up if I knew for a fact that it could be part of the problem.
Most digital repeaters clean up and reclock the digital signal before retransmitting it.
Not all repeaters do a good job on that. And remember "Garbage in Garbage out".
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