[grc] [Solved] Sound Quality Issues

[David Klann]

Thanks to everyone who weighed in on our "phase error"!

After continuing to chase this over the past month, it turns out that it
was not a wiring "phase" issue or really a hardware issue at all! Well,
it *was* a hardware issue, but way down in the depths of the central
processing unit(s) (CPU) of the audio workstation we are using.

At Ken's and others' suggestions, we used Audacity as sort of an
oscilloscope. We zoomed in on the audio tracks to the point where we
could see the individual samples as "dots" and found that the left and
right channels were out of sync. The channels were sufficiently out of
sync (a few milliseconds) that it sounded like a phase error. What the
heck would cause this?

I posted a similar call for help on the Linux Audio Users mailing list
(http://lists.linuxaudio.org/listinfo/linux-audio-user). One of the
replies on that list suggested turning off all but one of the CPUs on
our four-CPU workstation. That was the ticket: It was a timing error
introduced by the computer itself!

Lesson learned (for me anyway): be careful running audio applications on
multi-core computers (which most are these days), and make sure you know
well the hardware configuration of the computer!

Thanks again!

  ~David

On 11/10/2016 04:54 PM, Will Floyd wrote:
> Definitely sounds like a phase issue. Because of multiplexing that
> happens at the fm processor, a phasing issue up the chain will cause
> some wacky effects that are often less obvious to the ear. My
> recommendation would be to listen to the source before it undergoes any
> processing. I'd bet the culprit is a stereo balanced cable somewhere
> with one side mis-wired. 
> 
> On Thu, Nov 10, 2016 at 3:26 PM, David Klann via grc
> <grc at maillist.peak.org <mailto:grc at maillist.peak.org>> wrote:
> 
>     Greetings Fellow Radio Geniuses!
> 
>     We're running into an audio quality issue here at WDRT 91.9fm in rural
>     Western Wisconsin. I'm past the point of tearing my hair out in search
>     of the root cause. I'll outline what I can here, and answer further
>     questions as they come in. Thanks in advance for your thoughts and help
>     diagnosing this.
> 
>     Some facts:
> 
>      - The quality of *some* (not all) spoken-word audio recorded in our
>     "Studio B" sounds like it was recorded with the person speaking through
>     "a metal pipe while in a tunnel" (that's the best description we've been
>     able to come up with)
> 
>      - It *sometimes* depends on the radio people are listening to when it
>     happens
> 
>      - Music recorded in the same studio from any source (analog vinyl, CD,
>     digital source, etc) sounds just fine
> 
>      - One listener has noticed that it sounds "bad" when they listen with
>     their home receiver set to "mono" mode, and when they switch to "stereo"
>     mode it sounds fine
> 
>      - The same audio sent to our Internet stream *usually* sounds "normal",
>     but sometimes sounds "bad"
> 
>     This has been an otherwise productive exercise for us because we've
>     learned of a few other misconfigurations in our audio chain. But this
>     one continues to haunt.
> 
>     Again, I appreciate any thoughts you can share, and will provide more
>     info as requested. If off list, I'll summarize the "fix" to the list
>     when we figure this out.
> 
>     Thanks!
> 
>       ~David Klann
>        WDRT, 91.9fm, Viroqua, WI
> 
> 
> 
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>     <http://maillist.peak.org/mailman/listinfo/grc>
> 
> 
> 
> 
> -- 
> Will Floyd
> Technical Director | Prometheus Radio Project
> will at prometheusradio.org <mailto:will at prometheusradio.org> |
> 215.727.9620 x524

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