[RTTY] Reddit Article Showing Windows 7 and certain USB Audio Chipbug

[Joe Subich, W4TV]

The "bug report" is highly inaccurate and the instruction to
set the "microphone" level to 100% is completely *wrong*.

Right click on the microphone slider and set the display for
*decibels*.  In Windows 7 the microphone slider scale will range
from -196.0 dB at 0 to +30 dB at 100% while in Windows 8.1
the scale will be -96.0 dB to +30.0 dB.

Negative gain levels represent attenuation between the input of the
CODEC and the analog to digital converter while positive gain levels
represent excess gain.  Sands is completely *wrong* when he says any
value below 100% represents attenuation.  In fact, any value above
0.0 dB represents *GAIN* in the CODEC.

There is one "bug" in Windows 7 and prior - the USB Audio Class
driver will reset the gain of the endpoint (input) on any CODEC
that has a *single input identified as "microphone"* every time
the CODEC is opened.  This means Windows sets some members of the
TI PCM29xx family to +30 dB on each use.  *THIS BUG HAS BEEN FIXED*
in Windows 8 and later.

The best recommendation for setting USB levels for any "microphone"
input supported by the Windows "USB Audio Class" driver is:

- start the program that uses the sound card in question
- go to Control Panel | Sound | Recording tab, double click on
   Microphone - USB Audio Codec device
- on the Levels tab, right click on the microphone slider and
   set the units to *dB*
- adjust the slider for 0.0 dB +/- 0.5 dB - this will typically
   be 3% in Windows 7 and 54% in Windows 8.1
- tune to strong carrier (S9+)
- watch VU meter on Recording tab and adjust output level from the
   radio (typically the RX pot on the interface - "Line Out" in the
   K3/K3S) to 2 bars below full scale. If it not possible to reach
   2 bars below full scale (the K3/K3S has plenty of excess drive)
   increase the level slider slightly until signal is no more than
   2 bars below full scale.

I no longer have working XP or Vista systems and do not recommend
the use of obsolete operating systems.  However, the same procedure
(adjust for 0.0 +/- 0.5 dB) should also work with XP and Vista to
prevent overdrive and clipping there.

In any operating system, a 0 dB input gain setting will provide the
best balance of dynamic range and sensitivity in a sound card with
properly designed audio input circuits.  Audio from the transceiver
should be set so the no-signal "sky noise" is about 15 dB above the
noise floor of the CODEC and the strongest signals no more than "2
bars" below the top of the "VU Meter" to prevent clipping.

It may be more difficult to properly adjust levels in some Icom
transceivers that offer no hardware control of the audio levels
into the PCM29xx family than in external interfaces or the Kenwood
(and Elecraft K3S) transceivers that *do* provide control over the
audio level to the CODEC.

This "bug" *IS* a compelling reason to upgrade to Windows 8.1 or
Windows 10!

73,

    ... Joe, W4TV



On 2015-07-30 1:08 AM, 'Jim' jimw7ry at gmail.com [N1MMLogger-Digital] wrote:
> This was from the RTTY reflector. I though it would be appropriate for here too.  Both my IC7600 and new IC7410 have this issue.
>
> 73
> Jim W7RY
>
>
>
> Found this article on Reddit tonight.  Apparently this gentleman has
> discovered through some testing that certain TI chipsets used in some
> popular rigs and a popular USB interface may be causing serious errors in
> digital decoding.  There's a link to the Youtube video showing the bug, and
> how he's found a work around for it.  Apparently there's a possible issue
> with some Icom rigs with built in USB audio, as well as the Kenwood TS590
> series, and the Signalink USB Interface.
>
>
> https://www.reddit.com/r/amateurradio/comments/3eytah/huge_windows_bug_ruining_your_receive_performance/
>
>
>
>
>
> Charlie
>
> N5WE
>
>
>
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>