Monday, May 16, 2011

Noises now believed to be station problem, not reception problem

Synopsis: I brought two high performance FM tuners over to friend's house.  He lives near (or at least much nearer to) the KPAC transmitter, and in a different direction.  I heard the same two problems there using his antenna that I hear at home on my antenna: a buzz and a swishing sound.  These noises are fairly low in level (I'm guesstimating -45dB for the buzz and -55dB for the swishing sound) but strong enough to be very annoying on this otherwise wonderful sounding station which plays beautiful music with minimal compression.  I do not hear these sounds on other stations, even lower strength (at my home) college radio stations.  The noises are found in stereo mode only; in mono they go away entirely, and a good high blend feature can reduce them almost entirely.  The signal strengths at both locations (around 65dBf at my house, 69dBf at his) should be quiet enough for very quiet reception in stereo barring interference problems.  The fact that the noises are virtually identical at both locations using top notch equipment is strong evidence that this is a station problem and not an interference problem.  If it were an interference or signal condition problem, I would have expected his location to be rid of these noises.

I brought the Pioneer F-26 tuner because it is the best sounding and most transparent sounding tuner I have.  It is also low noise, perhaps the lowest noise from any tuner I have ever heard that isn't doing any kind of auto blending.  My F-26 was shipped direct to me from the top rated (by Tuner Information Center) tuner restorer, Absolute Sound Labs just a few weeks ago.  It sounds and works perfectly.  It also reveals the buzz sound more clearly than any other tuner...I believe that is because it is so transparent.  Other tuners reveal the buzz but often hard to hear amid hiss and random noises.  The F-26 was said to be one of the 3 greatest tuners of all time (the others being Sansui TU-X1 and Kenwood LO-2t) by tuner expert "anonymous Dave" at Tuner Information Center.  But in detailed notes, he believes the Pioneer has the most transparent midrange of the 3, so you could consider it *the* best.  (Since making that statement a few years ago, he's now onto the latest 2011 Accuphase shown at CES, he now thinks that may be the best.)  With any older tuners like mine, or even brand new ones, the devil is often in the actual condition and alignment.  With a recently restored and aligned unit, still under 6 month warranty, I have that devil handcuffed for awhile.

I brought the Kenwood 600T because it is also a great tuner and because it has the best meters of any tuner in my collection.  It has a signal strength meter calibrated in 10dB units (not exactly dBf, but Kenwood provided a chart for estimating dBf from the Kenwood dB numbers shown).  In my tests with a Sound Technology ST-1000A FM alignment generator, the dB meter is very linear and seemed about as accurate as I could determine.  You can read it to the closest 1 dB by visual interpolation.  It also has multipath and modulation meters.  It reveals the swishing sound a bit better than the Pioneer because it has a exaggerated high frequencies (or maybe a less good 15kHz lowpass filter or less good antibirdie filtering).

Friend lives in 2nd (upper) story in an apartment building, and uses a BIC Beam Box antenna and Pioneer F-9, and uses Carver preamp and poweramp, and some extra Carver gadgets (which were mostly turned off during these tests).  I also brought my own headphones and headphone amplifier (actually a Emu 0404 USB in standalone mode).

We first connected my Pioneer F-26 to his antenna and his stereo system.  It was a bit harder to hear on his AR-9 speakers (less transparent than my Acoustat 1+1's) but after a minute or so I was certain I was hearing the same buzz sound I hear on this station only.  I did not hear the swishing sound (it's always hard to hear on Pioneer F-26 for some reason, possibly because it has excellent SCA rejection.)  Then I connected the headphone amp and headphones to the tuner.  After about 15 minutes of concentrated listing (just before 12 midnight) I suspected I heard the swishing sound, but wasn't totally certain.  Unfortunately my dynamic headphones are not as transparent as my electrostatic speakers.  I also had a hard time hearing the swishing sound on the same headphones at my house (in fact, I didn't hear them at home on headphones for the first 15 minutes or so also).

We then hooked up the Kenwood to his antenna and electronics.  We found the signal level on the Kenwood meters was 60dB (which actually corresponds to about 65dBf).  Trying different settings on the Beam Box, we found that another position gave us 64dB (which would correspond to about 69dBf).  It seemed to make no signifcant difference on the multipath meter, which occasionally bounced a bit from the very bottom for all settings) so we went with that new position for the remaining tests.

The Kenwood also revealed the buzz though it was harder to hear because the Kenwood has considerably more hiss.  After about 10 minutes of non-equalized listening, I was pretty sure now I was hearing the swishing sound as well.  It's very irregular, you have to wait for situations where the music has been slowly fading away to a very low level.  When that happens, it seems the noise level (from the station or recording itself) rises (probably due to some compression at the station...they don't use a lot of compression, but apparently they use some).  When the noise level has risen like this, and if then there is a brief total silence, THEN you can hear the swishing, and even then it's often hard to hear unless your ears are right at the tweeters.

Then my friend engaged his normal EQ, which greatly boosts highs.  At that point I became quite certain I was hearing the swishing sound.  As this setup (AR-9 with boosted highs) seemed more revealing of high frequency problems than my headphones, I didn't bother with using my headphones with the Kenwood.

We didn't get around to using the rabbit ear antenna I had also brought.  My friend thinks his Beam Box Model 10 is better than such antennas, I'm not so sure.  But I don't think it would have made any difference in these tests.  The initial signal strength of 60dB (as per 600T meters) was exactly what I get at home, which I think considerably farther from the transmitter.  (Since writing this, I've determined my house is 21.7 miles from the 100,000 watt transmitter; I'd guesstimate friend's house is 10 miles but haven't gotten his coordinates yet; I had been expecting my home to be farther and his closer.)  Even the 64dB level we got after changing the Beam Box setting was less than you would expect for being 10 miles from a 100,000 watt transmitter (though that corresponds to 70dBf signal level which should be essentially "full quieting" in stereo for a good FM tuner, barring interference problems).

Both of these problems are eliminated by going into mono, and even using high blend (on some tuners, the F-26 has neither mono nor high blend controls) so it must some sort of noise that leaks into the L-R subcarrier at the station or wherever the stereo encoder is.

Investigations will continue.  Once I have digitally recorded and analyzed the noise, at least the continuous buzzing noise, I will send a letter to the station.

I've only actually noticed the buzz sound in the last 4 months when I got a Kenwood KT-6040, which was my favorite tuner for awhile (before I got the Pioneer F-26).  Perhaps I failed to notice it earlier because on less transparent tuners it is not as obvious, and also I had just spend a year listening to the Sony XDR-F1HD which does agressive blending and filtering to remove all noises.  Something like the swishing sound I have noticed for 18 years since I moved to San Antonio.  It does seem that with better tuners and better antennas the swishing sound gets less, while the buzz gets more and more clear.

In very quick testing, it didn't seem like the Carver FM stereo postprocessor TX1-11 (takes L and R audio signals from a tuner and then works some magic on them to reduce noise) made any improvement to either the buzz or the swishing.  Funny because I believe high blend would have made an improvement (though I couldn't test that either, because neither tuner I brought has a high blend switch..but in past tests at home high blend has greatly reduced the noises). Carver does claim the TX1-11 does not reduce stereo separation, so it is not the same as high blend.  This is further evidence, though I wouldn't suggest it's very strong, that the noises are *within* the stereo MPX itself, not something caused by interference or multipath, or else the Carver (if it works as claimed) should have reduced it.

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