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Old 14th Aug 2017, 1:27 pm   #1
stevehertz
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Default In what ways can tuner misalignment affect sound quality?

Regarding solid state hifi FM tuners, in what ways can tuner misalignment affect the final sound quality? I mean, if a tuner tunes in to stations and appears 'for all intents and purposes to work fine', yet the sound (for one example) is sibilant, what kind of problems in the tuner can cause that? or is it more likely to be a transmission issue such as multipath?
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Old 14th Aug 2017, 1:34 pm   #2
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Default Re: In what ways can tuner misalignment affect sound quality?

Poor AM rejection in the tuner can increase sibilance, it can also cause distortion, depends how poor the rejection is.
Faults in the de-emphasis circuit can also increase sibilance.

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Old 14th Aug 2017, 2:39 pm   #3
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Default Re: In what ways can tuner misalignment affect sound quality?

If the FM discriminator is not tuned to the IF then you get problems:
1. with AFC (so the signal is in the centre of the discriminator, but not the IF) the IF filters can add phase response problems which lead to audio distortion especially at higher frequencies,
2. without AFC (so the signal is tuned to the centre of the IF) the discriminator adds distortion on audio peaks.
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Old 14th Aug 2017, 2:41 pm   #4
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Default Re: In what ways can tuner misalignment affect sound quality?

These symptoms can also be caused by reception problems of course. Multipath is an obvious cause, but so is co-channel interference when a lift is on. Some tuners cope with these problems more successfully than others.
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Old 14th Aug 2017, 3:24 pm   #5
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Default Re: In what ways can tuner misalignment affect sound quality?

When a lift is on?
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Old 14th Aug 2017, 3:45 pm   #6
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Default Re: In what ways can tuner misalignment affect sound quality?

When radio signals travel much further than the standard service area, e.g. Tropospheric conditions, E layer conditions.

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Old 14th Aug 2017, 4:09 pm   #7
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Default Re: In what ways can tuner misalignment affect sound quality?

Having spent some hours realigning a valve FM receiver to work with a homemade stereo decoder, I would say that sibilance on FM transmissions is now standard. In search of the loudest possible audio, the audio is first heavily compressed then the pilot tone and stereo encoding is added. What happens next appears to be they wind up the volume until the transmitter clips the signal against the frequency bandwidth limits. A look on a scope shows virtually all of the popular music channels end up looking like a band across the screen with the encoded signal rattling from one extreme to the other.

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Old 14th Aug 2017, 4:22 pm   #8
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Default Re: In what ways can tuner misalignment affect sound quality?

Sibilance (when present) is actually most noticeable on female speech on R4. It would be relatively easy to mitigate this by de-essing in the studio processors, but nobody at the Beeb seems bothered about it. It's not obvious on digital platforms of course, which may explain the lack of interest.
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Old 14th Aug 2017, 5:36 pm   #9
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Default Re: In what ways can tuner misalignment affect sound quality?

I know someone whose natural voice contains significant sibilance. Fortunately she does not work in radio!
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Old 14th Aug 2017, 5:40 pm   #10
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Default Re: In what ways can tuner misalignment affect sound quality?

What happens in the event of a Hissy Fit?
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Old 14th Aug 2017, 6:10 pm   #11
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Default Re: In what ways can tuner misalignment affect sound quality?

My Sister in Law has just asked why I have suddenly burst out laughing. I couldn't explain.
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Old 14th Aug 2017, 7:19 pm   #12
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Default Re: In what ways can tuner misalignment affect sound quality?

It is possible for internally generated signals (birdies) may be heard on a digital tuner on
some spot frequencies.
The presence of a strong local signal is no guarantee that an adjacent channel transmission, albeit weaker, will not cause noises on stereo.
Example - I am line of site with CP (stronger than Wrotham here) and R4 93.2 gives
noise free reception. A pirate station on 93 (now gone) always caused irritating noises!
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Old 14th Aug 2017, 7:46 pm   #13
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Default Re: In what ways can tuner misalignment affect sound quality?

TBH I'm surprised that you surprised at that - only 0.3 Megs away? OK, the 93.2 station is stronger, but the other station is close.
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