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Why/what am I hearing?? -> Need common sense (again!)

Posted: Wed May 07, 2014 5:44 pm
by JJ2013
Hi y'all Audiophiles, Audioheads and VooDoo Gurus!!

Now, I am somewhat puzzled by the fact that I put a serious 60/60 (1 octave) cut at 8 kHz (= > cut affecting frequencies in the 4 kHz - 12 kHz range) just for the fun of it and it made a very big difference to what my audio sounded! Audio sounded horrible......does this suggest that although my transmitter (TS870) is incapable of passing 8 kHz I am effectively cutting "sub-harmonics" of 8 kHz, which would be 2 kHz?? Not sure if I am reading this right!! I would think that the Monitor on the 870 is pretty decent and that change would also be evident in the on-air signal?

So, I guess I am asking WHY does a cut at 8 kHz seem audibly so noticeable (or, is it that I only hear it when using the Monitor function of my TS870?) although the TX filters should not let 8 kHz through!?? Am I hearing a "cut" at a sub-harmonic of the 8 kHz center frequency which could be the aforementioned 2 kHz???

The reason for my placing a deep cut at 8 kHz was to help me get the ALC under better control (which it did not!)......

Would appreciate some clarity ;=)



P.S. Getting cuts/boosts more balanced (= no huge cuts nor boost) appeared to actually help with the ALC more!

Posted: Thu May 08, 2014 5:41 am
by Voodoo Guru
Howdy JJ,

You didn't specify what the negative gain level of the "serious" cut was, but guessing, lets say you made it -20db. You have to realize that at the 1 octave bandwidth, you have a broad curve traveling up and down the frequency spectrum from the deep center frequency -20db cut of 8kc. This dip starts at around 4kc at about -3db and ends up around 16kc at about -3db. Saying this, the 8kc cut will affect any other filters you have from around 3kc up and will change the way the final mix sounds as the affected frequencies are reduced in amplitude.

You also have to realize there is always a change in phase when you add or remove filters to the mix. This will also change the way the final mix "sounds".

So, since you have the center frequency at 8kc, you have the Bandwidth at 1 octave, and depending on the amount of gain cut, it will affect the audio mix all the way down to around 3kc.
This is why you are hearing a difference in the "sound" of the TX Monitor even though the rig only has a transmit bandwidth of around 3.5kc. Also remember that the TS-870 DSP does not have a "brick-wall" filter and you can easily push the soft knee of the high frequency transmit bandwidth filter of the DSP past its limit, so any frequency change in this area is easily noticeable.

If you are slamming the ALC on the rig, then it sounds like a gain structure issue in your Audio Chain feeding the TS-870. You might not have the gain structure adjusted properly and/or the compressor is not set up correctly.

Take Care,

Posted: Thu May 08, 2014 9:08 am
by JJ2013
Howdy VooDoo Guru :)

That's a common sensical response born of your countless hours of investigation, tweaking and retweaking to be sure!! AND, I see that I'd also not quite gotten the 1 octave right either in terms how wide the bandwidth actually is :oops:

The cut at 8 kHz was around 15 dB, but perhaps I try a cut at 6 kHz (and go narrower, say, 25/60) works better.

ALC is starting to behave a little better now (more balanced, the EQ is, with the "delta" between any individual cut and boost not being too large!). However, I am wondering about the mic pre-amp (using the MIC2200) in that should I go easier on the mic gain (it is around 17/18dB only since I am using a condenser mic) and crank up on the Output setting? I tend to think it is better if I don't use too much mic gain !!

In the end of the day (or night!), the condenser works much better for me than the broadcast quality dynamic I used before incidentally. A much more natural sound (people whom I've met know what I sound like) and there was even someone who told me that it sounds like FM which seems really crazy :wink:



Posted: Mon Apr 11, 2016 10:26 am
by !KANT
(I know, old post) But, I did have a question in regard to ALC. When monitoring the ALC on the '870, are you checking it while the transceiver is at FULL output power??