Pre-emphasis - ON or OFF - which is better on your radio?

[g8tzl2004]

The default Motorola setting for TX preemphasis and RX deemphasis seems to be ON

On some radios you can adjust BOTH TX and RX while on others there is just one setting.

Sometimes I think Motorola has implemented the preemphasis the wrong way round!!!

With my MCS2000, I have TX preemphasis ON and RX deemphasis OFF - the RX audio sounds brighter and less bassy on weaker signals although there is more hiss - but thats OK with me.

With my HT750/GP340, preemphasis NEEDS to be on - TX audio sounds terrible and muffled without preemphasis.

With my MTS2000 , I have preemphasis ON - RX audio sound less tinny

WIth my GM350, I have preemphasis OFF - TX audio sounds fantastic with it OFF and RX audio is very good!!!!

I wonder what settings others use for different radios?

[Astro Spectra]

The standard for LMR and indeed FM broadcast radio is to have pre-emphasis on TX and de-emphasis on RX.

The purpose of adding pre-emphasis to the audio feeding a FM transmitter and having matching de-emphasis applied the audio from the FM receiver is to improve the signal to noise of the received audio.

This process works because in FM there naturally is more noise or ‘hiss’ at the high frequency end of the audio spectrum than at the low frequency end. It gets worse as the input signal level drops as you move into weaker signal area. By shaping the TX audio to enhance (emphasise) the high frequency audio then apply de-emphasis at the receiver you cut back the FM noise while bring the audio high frequency signals back to normal. In other words the noise is cut back more than in the flat case improving the signal to noise ratio. You may not notice this effect unless you are listening to noisy signals.

If you leave RX de-emphasis off then not only will the audio sound like there is more treble but the hiss will increase more quickly in low signal areas. Also you may have trouble with DTMF detection with weaker signals because the decoder will be presented with the low and high tones out of balance (this is called twist).

If disabling TX pre-emphasis or RX de-emphasis seems to fix your audio then there is likely another problem that needs attention.

[g8tzl2004]

Thanks for the excellent feedback Astro Spectra.

I'm now wondering if pre-emphasis/de-emphasis only works 100% if all radios are the same model or make ie. everybody is using a Motorola??

On really weak signals, RX de-emphasis on my MCS2000 sounds very bassy and harder to copy than without de-emphasis - but the TX station/repeater might not be using pre-emphasis?? My MTS2000 handheld WITH RX de-emphasis sound "similar" to my MCS2000 WITHOUT RX de-emphasis. The MTS2000 WITHOUT RX de-emphasis sound very very tinny!!!

On all my Motorola radios, I always experiment when I first purchase the radio by programming the same frequency with and without pre-emphasis/de-emphasis and then toggle between all settings to see which sounds the best - and results do vary - well to my ears they do!!...but my testing is always using really weak DX signals.

[Astro Spectra]

No, the standard for LMR is well established and shared by all makers. It is set out in TIA/EIA-603-A “Land Mobile FM or PM Communications Equipment Measurement and Performance Standard” and is 6dB per octave (20dB per decade) between 300 Hz and 3000 Hz.

Note that the FM broadcast industry uses a different time constant arrangement and there is variation between the US and the rest of the world.

You might be interested to know that the same emphasis techniques are used in phono records, FM television, CD players, and many other systems.

A signal through a properly set-up repeater should sound as the same signal as on simplex.

Be aware that repeater operators and makers often attempt to enhance the repeater audio with various techniques including amplitude compression (limiting peak deviation) and boost (raising low deviations signals up to a more average level).

I not familiar enough with the MCS and MTS product to comment on the audio.

[MP 6.7]

You might be interested to know that the same emphasis techniques are used in phono records, FM television, CD players, and many other systems.

It's a fundamental technology in the old Dolby noise reduction systems back in the day of cassettes. Turning on the NR while playing a tape that wasn't recorded with the opposite Dolby NR EQ curve made the audio sound bassy and muffled. As was mentioned, phono preamps also have a de-emphasis circuit in them to reduce the inherent noise of the medium. The record is mastered with a high boost which is counteracted by the inverse cut made by the preamp which brings the highs back down to where they should be while taking the noise down the same amount.

[g8tzl2004]

So ..if pre-emphasis is like Dolby, if the TXing station is NOT using pre-emphasis, then you should NOT have RX de-emphasis enabled otherwise the RX signal will sound bassy and muffled??..I think this is what I am finding.

WIth my MCS2000, TX pre-emphasis ENABLED and RX de-emphasis DISABLED seems to get the best results..for my ears.

[WB6DGN]

"WIth my MCS2000, TX pre-emphasis ENABLED..."
You are transmitting audio boosted at 6db/octave, ie. highs emphasized. That's what OTHER people are going to hear and their receivers will "readjust that for flat response" by the deemphasis network in THEIR receivers.

"...and RX de-emphasis DISABLED..."
Your receiver is set for a flat response. That's what YOU are going to hear. You will hear an emphasis on the high frequencies which you told your receiver not to mess with.
What you are hearing is the higher audio frequencies boosted by 6db/octave (in my day, the "Treble" control turned up).

"... seems to get the best results..for my ears."
Wondering if you did (or do) mess around with hot cars (small/no mufflers)...or, maybe do a bit of target shooting?...or, maybe just getting up around my age? All of the above will cause the natural hearing to roll off at the higher frequencies and you are, in effect, compensating somewhat for that effect the same as turning up the treble control would do. No harm in setting your own receiver where it sounds best to you. Just be aware that that may not be the optimum setting for another listener.
Tom DGN

[g8tzl2004]

I can hear crickets and grasshoppers "chirping" when others hear nothing!!!

Maybe its the frequency responce of my MCS2000 external speaker?

I have numerous other LMR/ham radios , many of which have NO pre-emphasis option. On very weak signals , its only the MCS2000 which sounds bassy and muffles when de-emphasis is enabled. BUT maybe it would sound OK if the TXing station was
using TX pre-emphasis??

[PETNRDX]

It is NORMAL for all standard FM radios to TX with pre-emphasis.
And it is NORMAL for all these radios to de-emphasize.
As mentioned above, its is the industry standard and nearly all radios in the field are going to be using BOTH.
Only a couple newer radios have that as a programmable variable to not do so.
If your MCS sounds better with de-emp off, then there is likely a problem with that radio or its speaker.
I can't really think of a reason to change pre-emp or de-emp in a mobile or portable.
Some people do like to not process ( Pre-emp then De-emp ) within a repeater, from ITS Rx to ITS TX, and some like to transmit "flat" audio on links.
I would recommend you use pre-emphasis and de-emphasis as normal, and find out what might be wrong with that MCS radio.
There is a good reason ( explained in the previous posts ) it is used.
Things can sound really bad when there is a mis-match of emphasis.

[g8tzl2004]

I have 3 UHF and 2 VHF MCS2000's and the RX audio on WEAK SIGNALS all sound muffled and bassy when RX de-emphasis is enabled??

I've toggling between RX de-emphasis and NO de-emphasis and asked others in the room which sounds better and everybody says NO de-emphasis is best??

Maybe the MCS2000 has too much RX de-emphasis??

On medium/strong signals , RX de-emphasis sounds OK - its just really really weak DX signals that sound too muffled.

With my MTS2000 , when RX de-emphasis is DISABLED, the RX audio sounds very poor and tinny - so with my MTS2000, RX de-emphasis ENABLED sounds best.

WIth my Euro GM350 (like the GTX), NO pre-emhasis, NO de-emphasis sounds fantastic - I always get "you have great audio" reports!!