Narrow Band versus Wide Band = Audio ???

[Satelite]

Hello :
I sorta got the gist as to NB and wb but wondering about loudness of the audio at the mobiles speaker recieved.
Not mixing nb with wb but compareing the audio speaker output as compared to each.
And talking radio to radio as talk around and not through a repeater.
Ok say for reference two GM300 wb mobiles as the comparison on rx audio at the speaker recieved.
Would two GM300 nb mobiles be just as loud as the two wb mobiles to each other ?
Im asking about nb to nb mobile as to comparision of a wb mobile to a wb mobile not mixing the two with each other.
Reason i ask is that the deviation for Wide band is 5 khz where the deviation for 12.5 narrow Band is 2.5 khz.
Does the nb mobile amplify the rx audio more to be the same as a wide band ?
Hope i described my qestion well enough for you to get my drift.
Thank you
Satelite

[HLA]

if everything is the same then you shouldn't hear a difference. once you start mixing spacing then it gets ugly.

[jackhackett]

Ideally the speaker audio levels should be the same for narrow and wide band, whether they actually are depends on how well the radio is designed. The output from the discriminator will be lower for narrow band, so they need to amplify the audio more. If you look at the schematics for a GM300 you'll find that they change a few resistor values to increase the audio in the narrow band version.

[libuff]

lets say for example, you were using a XTS3.5k for Receive on some local Freqs. The local repeaters were Narrow Band 12.5khz, and you just indescriminately put all of your channels to 25khz, would the audio be lower than normal on the 12.5khz spacing boxes?

[Elroy Jetson]

A properly designed and aligned radio that supports both wideband and narrowband operation will use different gain levels in the audio output circuitry which result in the same effective audio output at the speaker,
regardless of mode.

Provided, of course, that the modulation levels of the signal being received are correct for the bandwidth. 100 percent modulation in wideband or 100 percent modulation in narrowband will sound the same IF the receiver is properly programmed for wideband and narrowband operation.


Interestingly enough, I've just learned the Bessel Null technique of setting modulation. If you have a calibrated digital audio signal generator and a spectrum analyzer and a certain handy little calculator program, you can accurately set modulation without a modulation meter.


Elroy

[libuff]

Elroy,

you almost lost me 100% there, but luckily, i was able to understand part of that...

you are saying (in my summation) that if my radio is programmed to receive 12.5khz audio, and it was receiving a true 12.5khz audio stream then it would sound the same as a 25khz channel receiving 25khz signal...


the question i am have is... if my radio were programmed to receive 25khz on a channel which in fact is transmitting 12.5khz... what would be the result of the audio...

i am trying to internally (in my head) figure out why some channels are coming in quite low, compared to others... the low audio channels are usually newer repeaters, i assume complying with the 12.5khz spacing...

[Elroy Jetson]

A radio that "doesn't know it's hearing a narrowband signal" would have low receive audio when receiving that signal.


The narrowband signal looks exactly like a signal with LOW MODULATION.

You could almost say that the significant difference in a radio between narrow and wideband operation is that a radio that is designed for narrowband operation will have more audio gain in the receiver and may not be able
to set its TX deviation to the wideband values while in narrowband mode. Otherwise, there's hardly any difference at all.


Elroy

[Larry Page]

Changing gain in audio amps can, in fact, bring the NB audio up to the same level as wide band audio as has been stated above. The extra gain, however, acts on everything that comes out of the discriminator...including any noise in the signal. So if 3 dB of gain is added to bring the recovered audio volume back up, any noise included in the signal is increased by 3 dB also. This is enough to produce a noticeably poorer signal (if everything was perfect in the wideband radio).

The other thing that has to happen when converting to narrowband is that the maximum modulating frequency has to be reduced. This will result in an even more noticeable degradation in recovered audio quality and intelligibility.

"Hear Clear" and other signal processing and encoding options can work to minimize the impact of moving to narrowband operation by shifting to a non-linear modulation / demodulation technique or by pre-processing and post-processing the audio signal (like Dolby FM or the old dbx-encoded disks and tapes).

It will be interesting to see what further developments to enhance audio emerge in coming years. Remember...it wasn't too long ago that a well known theorem "proved" that data rates greater than 300 baud could never be achieved in the 3kHz bandwidth of a standard telephone voice channel.

Regards,
LP

[Elroy Jetson]

Multiplexing is a wonderful thing.

Yes, you're right on everything you said and I did know it, but I chose to keep it simple in this case. Just the basics.

Both amplitude compandering and non-linear frequency shifting are needed
in order for narrowband to REALLY compete with wideband transmissions in terms of audio quality. I'm sure that HearClear uses amplitude compandering but I don't know if it uses non-linear frequency shifting or not.

Simpy amplifying everything more isn't the best answer. You amplify the
noise as well as the signal, so your S/N ratio doesn't change. That's why
we don't all have radios with nanovolt sensitivity receivers.

CJ