View Full Version : FM Sibilance?


DKak
07-12-2005, 05:53 PM
I have a reasonable collection of nice tuners, and they all have issues with sibilance in stereo. Generally heard most easily when it's just a voice speaking.

Sounds like overmodulation or some other broadcast issue, right? Especially when all the tuners are doing it and the one station where you rarely hear it is a public station that goes out of its way to broadcast a good signal. Bouncing the problem off a few people who know tuners and radio well, they agree.

But I keep coming back to the fact that NONE of the tuners exhibit the sibilant sounds when they're set to mono.

What might cause this? Is it something in the subcarrier that causes this? Does anyone have any ideas? Is it curable in an alignment? :dunno:

skippy_ps
07-12-2005, 06:21 PM
My TU-517 does this noticeably more than my McIntosh turners although the Mc tuners have been aligned while the Sansui has not. Seems to be worse with male announcers than female.

Don't know why or how this occurs.

Murray

ginovino
07-12-2005, 08:14 PM
I hear the sibilance more readily with my receivers.

I have heard it sparingly on my Kenwood 600T and less so if at all on my Sansui Tu 919 & 9900's. All three units have been modded and updated though as have the receivers.

More importantly, is tuner shielding. All of my receivers have an unfortunate condition of having I.F. freq of 10.7mhz which is multiplied 9x = 96.3mhz exactly the frequency of the best and only full time classical broadcasting station in NYC. Their signal is about the best in NYC, but when no modulation occurs you can hear the back ground "birdie chirps & whistles" of the I.F.'s

This behavior doesn't occur on my "tuners". Silence black as night!

any suggestions out there?

I have a roof top Omni Dipole via RG-6 quad into a 90db isolation switcher to select tuners, receivers etc. :scratch2:

doucanoe
07-12-2005, 09:18 PM
Hey DKak, One question, are you using analog tuners or digital?

RC

DKak
07-12-2005, 10:09 PM
Hey DKak, One question, are you using analog tuners or digital?
RC

The only digital tuner I have is a Sumo Charlie. The rest are Marantz, Heathkit, Magnum Dynalab, Sansui, Pioneer, et al, all analog. In the "What tuners do you have" thread I listed them all.

The Charlie has all of James Bongiorno's updates to the RF section, and he aligned it and stated its performance was one of the best he's done. Extremely quiet and low distortion in his estimation. I must say, it is darn quiet. Its stereo sibilance is a little bit less than the analog tuners, but it's still there.

doucanoe
07-12-2005, 11:01 PM
In town here, there are a few public radio stations that I listen to. One being a Jazz station, one Classical and the other college. All others are broadcasting a terribly compressed signal and they sound like crap.
I think the idea is the most people are listening in cars through marginal systems so loud and louder is better.
I will have to listen for a while (if I can do it without putting a gun to my head) to a few pop/rock stations and see if I hear any sibilance in voices.

Ill let ya know.

RC

DKak
07-12-2005, 11:14 PM
I hear it most easily when the DJ is speaking. But it's quite audible, too, when a cymbal crashes in one channel. If I'm wearing cans, as is usually the case at night, it is noticable to the point of being distracting.

FWIW, the sibilant "S" sound comes from either the L, R or both channels, although the DJ is speaking dead center. I haven't noticed the sibilant "S" sound coming from the center where the DJ's voice is. Of course, all of this is with the tuner in stereo. I don't hear it at all in mono.

I should mention that I have a very good antenna on a rotor and I have a Magnum Signal Sleuth which can be switched in or out. I use an oscilloscope with the scope outputs of my Pioneer or Sansui tuners (or use the one built into the Marantz) to best aim my antenna and tune out multipath. Signal quality is very good in general.

mamboze1
07-18-2005, 06:07 AM
If the sibilance is present in all the tuners (and you've got some good ones there, for sure) and the signal strength is adequate, then the problem may be downstream. Have you checked the cables and the amp? I presume that you are getting the effect both in headphones and speakers which would rule out either of those.

DanTana
07-18-2005, 06:17 AM
What you could be hearing is the compression some stations use for broadcasting. Try listening to your local NPR or classical stations and see if you hear the same noise.

juncers
07-18-2005, 07:16 AM
Is the sibilance at high power only ( over 5 % of its rated output) or is it there at low power also? I was taught that sibilance is a function of crossover distortion with type AB transistor
amps. Just a thought...

Ray

DKak
07-24-2005, 01:25 PM
If the sibilance is present in all the tuners (and you've got some good ones there, for sure) and the signal strength is adequate, then the problem may be downstream. Have you checked the cables and the amp? I presume that you are getting the effect both in headphones and speakers which would rule out either of those.

Sorry...was away for a week with no PC access.

Cables, preamp, amps, power supplies...all are very good and running well. Besides, you can get rid of the sibilance by selecting mono on any of the tuners. I suspect maybe it's overmodulation, something in the subcarrier signal or how it's received...or something else??? Anyone?

We have a few public stations which broadcast decent signals (Denver metro area). The sibilance is very slight on them, kind of leading me to the overmodulation thought. But I'm not an expert in any way on this...was naively hoping for that magic bullet which says, "Oh, just do such and such and it's gone for good."

dshoaf
07-25-2005, 02:58 PM
I've had a problem with this sort of problem with my MX-110, a Pioneer TX-8500II and a Dynaco FM-5. All exhibited the same sort of 'smeared' audio in stereo but not in mono.

Tracked it all down to the digital devices I'm using between my PC and the whole stereo setup: An outboard DAC - USB based - and a Slim Devices SqueezeBox2. Both appear to be generating a fair amount of noise that's really driving the tuner's demux circuits crazy. I'm turning off the SB2, unplugging the power supply and disconnecting the DAC and its power supply to get it to work well.

Yeah, I know, shielding, etc would help but I mention this here for someone else to consider for their problems.

Cheers,

David

crooner
07-29-2005, 02:15 AM
Sibilance. You can minimize it, yes. Get rid of it completely? No.
It's part of the human voice...

lasminit2
07-30-2005, 12:30 PM
Multipath distortion can cause a garbling of mid-hi frequencies and would be extremely audible on voice, and largely disappear in mono. The better the antenna and orientation, the less problem you would have. Having said that, most people (even lots of experienced DJ's) have poor mic manners...they bob their heads while talking,sometimes "eating" the mic, sometimes moving too far away. The poor engineer can only average for this, but over- and under-modulation are the inevitable result, so out come the compressors, sometimes helping but often making voices sound extremely unnatural. Anyway, it could well be either or some of both problems. Since a good alignment and antenna will cure virtually all of the multipath, that might be a good place to start. The mic manners we can't do much about.
Take Care,
Richard

DKak
07-30-2005, 11:04 PM
Since a good alignment and antenna will cure virtually all of the multipath, that might be a good place to start. The mic manners we can't do much about.

Yeah, two tuners are at Punker X's now for mods and alignments, will send another when they're done and funds allow.

And a couple local public stations have pretty darn good fidelity. Was just hoping that I might do better on a few others...

Thanks to all for ideas and input!