Digital Voice quality
- Thread starter xantegh
- Start date
Because of the nature of low-bit rate digital audio. AMBE/AMBE+2 vocoding commonly used by DMR and P25 has a variable bit rate of between 2 and 9.6 kbps depending on configuration, whereas CD quality bit rate is 1,411 kbps (uncompressed). This is a simplified comparison, but you get the idea.Folks,
Why most if not all of the audio streaming of digital communication systems used by Police, EMS and others such as P25, DMR, etc. sounds like robots. I can hardly understand a thing from their conversation due to this robotic quality.
Example for your reference:
OpenMHz
openmhz.com
It's the streaming degrading the quality, not an issue with P25 or DMR. I've heard a DMR system I use over an internet stream, and it was no where near the quality delivered to my radio. Streamers are mostly using consumer grade scanners and PCs to provide the feed, not necessarily of high quality. Add to that, the bandwidth of their internet connection may be less than needed to pass quality audio, and they are trying to pass an re-digitized digital sound.
When you listen to digital broadcasts on a cop radio in P25, DMR, etc, it doesn’t sound that bad. Police scanners take a hit in audio demos and quality and emphasizes the robot sound.
The best digital audio I've heard from a consumer level hardware receiver is from the Icom IC-R8600. The SDS200 with audio passing via its ethernet connection to ProScan does a nice job as well. (Actually both are SDR's) But the best overall P25 audio I have ever heard comes from the OP25 software, and SDRTrunk hangs in there pretty well also (and with DMR as well). What internet latency etc. does to it after that is out of the feed provider's hands at that point. A lot of the streams on the Broadcastify Calls platform use these software setups and I think many of them sound very good. All of the above is my ears at work, your mileage may vary.
Ubbe
Member
I listened to the radio communication from the Baltimore bridge incident and the audio quality where terrible. They seemed to use noise reduction in their transmit audio as the background sounds where muted in a way that indicated sound processing and that made the voice audio also being stripped from important details.
I've tested both having noise reduction on and off in really high noise level machine industries in customer radios I have programmed and even if the background can be heard when the noise reduction are off, the voice quality are so much higher that it compensates many times over in voice recognition. For the Tetra systems we use here there's HiFi voice quality compared to many other digital system types. It sounds with the same audio quality as it would had been an analog system.
/Ubbe
I've tested both having noise reduction on and off in really high noise level machine industries in customer radios I have programmed and even if the background can be heard when the noise reduction are off, the voice quality are so much higher that it compensates many times over in voice recognition. For the Tetra systems we use here there's HiFi voice quality compared to many other digital system types. It sounds with the same audio quality as it would had been an analog system.
/Ubbe
Here's my opinion on digital audio in general - it's pretty much a gimmick. I realize that me listening to digital EMS comms on my Brearcat scanner give me a generic output from a generic vocoder. The proponents of digital audio say 'it's better, more flexible, etc'. I am convinced that digital audio in EMS radio comms is mostly a waste of our tax money and a gimmick allowing Motorola and other vendors to sell new expensive radio equipment that is really not needed. Plain old FM modulation as invented by Edwin Armstrong almost 100 years ago not only is all that's necessary, and it offers advantages over digital. The radio vendors have been pushing digital 'snake oil' radio as being 'interoperable'. Hogwash - any narrowband FM transceiver can communicate with any other nb FM on any given frequency. There also a new problem introduced by digital audio - susceptibility to background noise. There are a lot of instances where emergency personnel need to communicate on their comm equipment in a noisy environment - with more noise than can be removed from a quality microphone and digital signal processing. One true 'advantage' of digital audio is that it allows encryption of the audio that is secure enough that it cannot be intercepted by third parties. While there -might- be a genuinely valid reason for this, all our police, fire and EMS personnel actually work for us the taxpayer. I'm not attempting to discount the importance of these service or the bravery shown from them all, but in a free country, the citizens have the right to be able to monitor most radio comms. de N2EPV
You would really need to sit down at the person's PC and hear the audio being decoded, before it's streamed, to make any kind of finger pointing statement. Streamer may not have the best signal, or enough PC resources (cpu, ram) to decode and run a feed. Could be many reasons. Could be ISP related. Many of the feeds out there sound great. Many factors involved with decoding signals and running a feed.
chrismol1
P25 TruCking!
- Joined
- Mar 15, 2008
- Messages
- 1,357
my sdr trunk on my PC sounds slightly different than the streams on broadcastify or openmhz. Worse is I remember my first time hearing P25 digital on a scanner then an SDR and hearing the audio from the SDR program and thinking wow how good that was. Then getting a real motorola XTS radio to listen to P25 and realizing how bad I didn't realize it was....Then I got an APX and realized how bad the XTS was...haha. and when I mean bad, it was just the progression of technology and better components. I'm sure professional music audio people can say the same thing thru various equipment.
The audio coming out of my actual professional radio sounds different than any other source. You simply cannot say a system is bad because of how it sounds on consumer equipment.
The audio coming out of my actual professional radio sounds different than any other source. You simply cannot say a system is bad because of how it sounds on consumer equipment.
Ubbe
Member
I could clearly hear that it was not a decode issue, bad RF signal level or bit errors. It was a sound processing noise reduction system working at the transmit side that really massacred the speech audio. There's probably better working digital P25 system but the mobile/portable they use at the Baltimore incident need to be programmed differently or use another brand or model of radio. If I where to do a final acceptance test with a customer having this audio quality the system would fail to get approved.
/Ubbe
There are four local and one statewide TRS systems supporting this incident, plus various federal agency simplex and multicast communication systems. There is a communications support van set up on top of a trestle portion of the bridge that did not collapse. It's likely a crossband patching system. Lots of vectors for degradation. The specific audio you are hearing originated from the Maryland statewide 700 MHz system that has two physical subsites from two separate simulcast sites within a few miles of the bridge. One tower site is at the Dundalk Marine Terminal which can been seen in the backround in images taken of the disaster. The quality captured on the Youtube video is not typical: it probably reflects issues with the receiving system that feeds the streaming service that published the audio.
nd5y
Member
How much of the bad digital audio is caused by manufacturers using cheap crappy speakers?
Ubbe
Member
I went to Broadcastify and listened to Baltimore streams and it was equally bad, but that's probably the exact stream that where captured in the Youtube video. Went to other counties in Maryland and sounded just as bad. I really hope for the users sake that it doesn't sound like that in their radios. I heard one mobile actually having acceptable audio, perhaps a portable, but 4-5 others sounded real bad and the dispatcher was actually the worse one among those.
/Ubbe
/Ubbe
