Why Do Digital Modes Sound Quiet And Muffled Compared To Analog?

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Whether it's P25, DMR, or whatever, digital modes always sound quieter and more muffled than analog. Digital lacks the crisp clearness that plain old analog seems to have. With digital modes, it always sounds like the treble is turned down all the way and the bass is up too high. Or it sounds like they're talking into a towel. Why?

I find that to really hear digital, you always have to put the volume up a lot higher than with analog. Agree, or disagree?
 
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Depends on the user and the gain setting of the microphone. Remember, an analog telco line sampling equivalent is at 64 kbps while digital over the air rates are less than 9.6 kbps. Anyway, on 90% of the subscribers, the mic gain is left at its default value which can lead to the muffled audio but it's very depending on the users and how far away they place the microphone from their mouth.


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jonwienke

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Strongly disagree. On the systems I monitor, digital channels average 3-5dB louder than analog channels.
 

ofd8001

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I suppose it's all how someone "hears" it or what their ears are used to. There is definitely a difference between the two.

Personally I'd just as soon listen to digital, because there isn't the "scratchiness" of analog, particularly at the fringes. "Back in the day" folks used to strive for "full quieting" or minimal static in analog. Because digital is a whole 'nother animal, the digital signal will never have static.
 

lucky43113

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Whether it's P25, DMR, or whatever, digital modes always sound quieter and more muffled than analog. Digital lacks the crisp clearness that plain old analog seems to have. With digital modes, it always sounds like the treble is turned down all the way and the bass is up too high. Or it sounds like they're talking into a towel. Why?

I find that to really hear digital, you always have to put the volume up a lot higher than with analog. Agree, or disagree?
Digital is not as clear as analog thats for sure. No one in my area likes it including cops and dispatch
 

AC9BX

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With analog it is often desired to have a high modulation level. For both AM and FM there's usefulness in being *loud*. For FM using all of the available deviation helps cover noise on the receive end and can improve *receivability* when the signal is weak. Level compression can be used to raise the average of the audio. However, when one exceeds the maximum occupied bandwidth naughty things happen, bad audio in the receiver, interference to others, etc. So radios normally have some form of limiter. Hitting the limiter too hard results in clipping. Clipping in an analog system is less offensive than digital. High levels in analog radio are commonplace. Since communications radios are not exactly hifi added distortion from limiting and leveling and clipping doesn't show itself very much.
In a digital system there is no atmospheric noise in the signal, no need for loudness. To avoid digital clipping, which sounds horrible, a nominal audio level is chosen, say -12dB, to offer headroom so loud sounds can pass without clipping. Compression is sometimes used just for maintaining a comfortable listening range. However, some people drive their radios much higher, peaking at maximum often or even overdriven as they would with FM. Yet others drive the radio much lower.
Small hand held radios seldom have audio settings. But most modern mobile or base stations units do.
In my area most digital users yield a similar level as FM on my radio. But some digital, and even some analog, are much louder while others are much softer.
Then there's the compression, in either digital or analog, used to raise the average, if for different reasons. A signal with high compression will sound louder compared to one without even though the peak is the same.
As for *crispness*, this is a function of bit rate for the compression codec being used. Very low bit rates make it difficult to have high frequencies. However, FM suffers too from trying to squeeze more in the spectrum. Narrow FM, with small modulation indexes have an audio bandwidth about half to a quarter of the occupied radio bandwidth. Example occupied bandwidth, 3kHz intended deviation with 3kHz audio gives 12kHz total occupied bandwidth, just barely fitting inside a 12.5kHz channel. So you can't get crisp audio here either.
I often find public service P25 to be way too bassy, silly useless big booming bass from typical comms microphones even though the radio's 2 inch speaker can't reproduce it. I suspect it's used as a selling point. Amateur use P25 doesn't seem to sound the same despite some having much better microphones.
 

RFI-EMI-GUY

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I hate the sound of digital audio compared to the old analog FM or even analog NFM.
I agree. The old "wide" 5 KHZ FM got the job done. There are some RF coverage advantages to P25 over the narrow 2.5 KHZ, but at the expense of intelligibility. P25 sometimes sounds perfect, but it has a lot to do with the voice of the operator, low ambient noise and Low bit error. Otherwise, to my ears, it hurts.

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W8RMH

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The P25 in my area is inconsistent. Sometimes it's as clear as analog, sometimes all broken up and intelligible, or either too soft or too loud.

The DMR has great range, is very clear, and doesn't sound digital at all.

I miss the days of FM low band and 100-watt mobiles.
 

paulears

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We cannot even agree on what wide and narrow even mean with contemporary radios - are we talking 'old' wide, as in the old 25KHz deviation level, where 'narrow' was the reduction in bandwidth for 12.5KHz channels, while now narrow is even narrower. Programming new radios is always worth a check - some programmers will be setting 'narrow' because they've always set narrow, and I did it too, until I realised that Kenwood 'wide' in analogue is a much better match for some Icom 'narrow' radios, just a few years older!

I use both walkie talkie style radios and In-ear Monitor systems, and the difference in quality is huge. The IEMs, designed for audio quality are pretty transparent - with ear moulds transducers that cost the same as the receiver, quality can be very high - but at this level, the commanders fitted to maximise dynamic range need to track well together, or the audio sounds wrong - over compressed or worse, over dynamic. All this with a 20-15K audio bandwidth. Moving to comms, and because it's essentially speech, the bottom below 300Hz isn't just reduced, it's removed so the tone signalling works properly - with some CTCSS tones over 200Hz! Again - there's very little useful information above 4K, and Bell discovered this a very long time ago, so it can be rolled off - not removed this time, just gently filtered off. Move to digital and new problems jump up. The audio brigade continually slag off compressed formats like mp3 - because it's throwing away data, yet to most people - it still sounds good. You can select how many times a second you sample the audio, and how accurate in terms of different steps of loudness you make the sampling. The common goal is to sample at twice the highest frequency as a good compromise - this is still quite a high data rate to send as RF in a limited bandwidth maintaining a low error rate end to end, so the designers can tweak that cut off to the highest frequency to manage the data stream. With limited resolution in bit depth, they also need to compress the audio pretty severely, digitise it, transmit it, then reconstitute it and that's a very large amount of wrangling to get it back. You can see how a manufacturer simply designs their entire processing train to be their version of 'best'. If they wish to increase intelligibility and add crispness and reduce the robotic sound, they can do it - BUT - at a cost. Something else has to go, or suffer. They all pick a different point on the good to bad scale, and it gets worse when you mix design philosophies. The SDR systems that decode lots of digital formats cannot do it properly - they have no way of telling if it's a Motorola or something else running Motorola's version of the protocol. Mismatching cut off frequencies, filter curves, companding ratios and processing means they really don't play well between models, let alone brands or a specification. Sometimes mismatches work for you - usually it will be the expansion process not matching the compression at the transmitter. Over expanding can give what appears to be cleaner speech, at the expense of maybe a little extra distortion - an error the other way softens the response making it appear muffled or difficult to understand. It was simple in the old days, when was that? Last year?
 
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Digital

My question is why did the public service sector radio manufacturers industry accept these bandwith restricted IMBE/AMBE voice quality codecs as the industry standard in the first place? For these critical emergency comms transmissions where audio clarity is so important. They just lop off every freq above 3khz, even worse than AM radio. It should have been a slightly better quality audio codec IMHO for the enormously huge licensing fees involved for each field radio. Or our scanners just can't equal the quality of the public service field radios. I know it was the FCC, "We need to conserve the bandwith spectrum for other (higher paying users)". Cram more voice channels into less actual Mhz spectrum. Cost a fortune and degraded the audio quality. And then add the DVSI licensing fees, like the cable box rental fee you pay each month but for every radio in use by every single police/fire/EMS agent using a P-25 radio. The old analog VHF/UHF radios were bought and paid for once, with probably a small engineering service contract fee thrown in. Now taxpayers will pay extra for all those new (per user radio) DVSI licensing fees each year.

The FCC wanted to squeeze public service radio channels to later sell it off as "Ocean Front" frequency spectrum for top dollars to the wireless (cellular data) industry players to give us faster internet on our smartphones. This is why digital P-25 sounds like it does. The trade off here was more available channels to use in less frequency spectrum with added reductions in broadcast (received signals) noise/static. Plus the real goal (it seems) is true agency interoperability, where cities/towns can now actually talk to each other and not have a hodge podge of differing frequencies/non compatible radios of various agencies on different channels. I can see this was what the FCC/industry wanted by coaxing a shift to digital radio systems. To have all local agencies be able to talk to each other in critical emergencies on fully compatible advanced radios with optional encryption if desired. This is logical. I do not much welcome the encryption aspect side but there are legitimate reasons for it. That is a different argument.

There exists a future possibility that digital signal processing DSP may be able to enhance the audio quality of digital P-25, etc, signals by generating/adding in missing harmonics as is done with say "chorus guitar pedals" or a various "adjustable gizmo harmonic synthesizers" at the DSP chip's audio output, where the scanner user could adjust it, like EQ. Everything else is fully adjustable/complex on these digital scanners. Why don't they add some form of advanced parametric Audio EQ DSP circuitry for us to mess with on these things? I know they can slightly improve the voice clarity on digital scanners, I doubt it would be cost prohibitive. I will do my part and keep complaining.

To AC9BX...Brilliant post. Clear, precise, accurate explanation. I can actually hear it when the comms clip their audio at the mic/console output going into the system IMBE/AMBE codec. The fractional audio dropouts start due to codec running out of encoding bits to use in the stream as they exceed the digital Ref level of (-15 db). In other words, they're "Over Peak" audio going in and run out of headroom (digital bits). This is still broadcasting. Some operators know how to self normalize their own voice, evening the levels out at all times, even in crisis mode, which means they sound clearer on digital. That is a pro.
 

KC3ECJ

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At an old job I got to use the Motorola XPR3000. I have found that DMR cant handle popping sounds well. Any word with P or some wind and the audio falls apart. If you have a DMR radio as a base station, using a pop filter would be a good idea.
 

paulears

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This is still broadcasting. Some operators know how to self normalize their own voice, evening the levels out at all times, even in crisis mode, which means they sound clearer on digital. That is a pro.
Comms is NOT broadcasting. If you fly in light aircraft, the audio quality is poor, the ambient noise high and even the headset to headset quality isn't brilliant. Squeeze it down an AM pipe to another aircraft and it's pretty horrible, yet the users alter their speech patterns to maximise communication success rates. They take exams in it, and those people who cannot do it always sound instantly amateur vs professional.

The typical radio user is not a professional communicator - that is not their skill area. Some have the mic a foot away, others touch their lips onto the opening in the case and bellow. The better (and more skilled) operators do like the air band folk - modify their speech patterns like RF-Guy says, but marine band shows how terrible some people are - clearly either too far from the mic, talking into the back of the mic, using equipment that badly needs alignment - who knows - but it goes from mega loud to almost just carrier. Digital radios seem to cope worse than analogue. My Kenwoods are more mellow on digital, but clear enough I think. They just sound different.
 

ChrisABQ

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As you can hear analog at distance, the further away, the more snow you hear. With digital, you either hear it or you don't. Since getting back in the hobby, I have been listening to my BCT15X FAR MORE than my own cities EDACS ProVoice system. I find it very difficult to listen to digital.

My fun has been listening to the ton's of analog that surrounds the city and listening at distance.

Thank God for poor counties.
 
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With digital, you either hear it or you don't
If that were true, digital communications would be much worse off than it actually is. You have packet error instead of analog white noise. You get to a point where it gets worse and worse. It can be bad enough to cause a reproduced frequency to become inverted or parts of the reproduction to become garbled. It's not just a there and gone thing though.

My question is why did the public service sector radio manufacturers industry accept these bandwith restricted IMBE/AMBE voice quality codecs as the industry standard in the first place?

There exists a future possibility that digital signal processing DSP may be able to enhance the audio quality of digital P-25, etc, signals by generating/adding in missing harmonics as is done with say "chorus guitar pedals" or a various "adjustable gizmo harmonic synthesizers" at the DSP chip's audio output, where the scanner user could adjust it, like EQ. Everything else is fully adjustable/complex on these digital scanners. Why don't they add some form of advanced parametric Audio EQ DSP circuitry for us to mess with on these things? I know they can slightly improve the voice clarity on digital scanners, I doubt it would be cost prohibitive. I will do my part and keep complaining.
Why was it chosen? That was the best technology at the time (remember, the P25 protocol is over 20 years old). Oh yea, DSP firmware updates have gone a long way in improving the quality of the audio on the subscriber side of the issue. Compare my Astro Spectra (DSP R07.xx.xx) to my XTL5000 (DSP R11.xx.xx) and it's a night and day difference. Compare my XTL to my XTS (DSP R19.50.00) and it's still a night and day difference.
 
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som

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What I want to know is why do some transmissions from airline pilots in the cockpit sound loud and clear as a bell? Almost like they're coming through on an expensive hi-fi stereo system. I'll be scanning through a bunch of muffled and scratchy local frequencies, then suddenly I hit on an aircraft frequency and it sounds like they're right in the room with me!
 

RFI-EMI-GUY

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What I want to know is why do some transmissions from airline pilots in the cockpit sound loud and clear as a bell? Almost like they're coming through on an expensive hi-fi stereo system. I'll be scanning through a bunch of muffled and scratchy local frequencies, then suddenly I hit on an aircraft frequency and it sounds like they're right in the room with me!
Receiving signals directly from aircraft are usually free from any multipath distortion and the signal unimpeded from terrain or blockage. So the signal strength is high and without noise. Usually the transmissions from the control towers are much weaker in comparison.

It is a wideband AM signal so the bandwidth is unimpaired. The microphones are high quality and noise cancelling. Usually there will be some 400 Hz alternator hum on the signal which guarantees you are hearing an aircraft.



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