Larry,
I emailed a step-by-step article to Neal today for consideration as a
possible addition to the Flex Wiki. Most people do exactly what you and
I did, plug in a mic, adjust the mic slider in the GUI, and run with it.
The necessary information is spread throughout the manual, but as I
recall, it's not all in one place. Besides, how many Flex users actually
read the entire manual? What I came up with is pasted below.
73,
Rob W1AEX
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Audio Gain Distribution Inside PowerSDR:
I have encountered lots of Flex/SDR users on the air who sound great in
every voice mode. However, it’s not uncommon to hear stations who seem
to have a lot of grit, distortion, and harshness in their audio in all
the voice modes. As it turns out, many of these stations are completely
unaware of the multi-function TX meter and how to use it to correctly
set the audio gain distribution throughout the Power SDR audio chain.
It’s not unusual to find that one of the stages is inadvertently running
at maximum gain while another stage is set near the minimum to
compensate. This can invoke strange events such as ringing in the audio,
distortion, and aggressive ALC action with pumping and audio artifacts.
I certainly don’t know everything there is to know about squeezing the
most out of the audio functions in Power SDR, but I did find that
balancing the gain from start to finish has brought very satisfactory
results for me and a number of others who were becoming very frustrated.
Pages 77 and 78 of the 2.x.x Power SDR manual "sort of" infer the
information given below, but I have found that many users are completely
unaware of any audio level settings beyond the front panel Mic slider.
Hopefully the steps below will help someone to avoid a disappointing
result when they start to transmit!
1. Connect the Flex to a 50 ohm dummy load and select one of the voice
modes in Power SDR. Make sure that you have a TX profile selected that
has your bandwidth set as you deem appropriate for the phone mode you
are using.
2. If you have either the “DX” or “Compander” button selected on the
front panel of Power SDR, unselect it now.
3. The “Mic” slider on the Power SDR front panel GUI is scaled from 0 to
70. Place it at the mid-point value of 35.
4. In the upper right corner of the Power SDR interface use the TX
dropdown in the meter to select "Mic”. This allows you to view the level
of the first audio stage of your Flex.
5. From the dropdown menus along the top left edge of the Power SDR
interface, select “Mixer” and position it on your desktop so you can
access it easily. With the Flex connected to a dummy load, key the
transceiver and speak into the microphone at the voice level you
typically use on the air. Observe the TX meter “Mic” level and adjust
your level up or down with the “Mic” input level slider (or the slider
for whichever input you are using) in the Mixer so that the maximum
peaks reach no more than –2 dBm.
6. Now set the TX meter to “EQ”. This allows you to view the level of
your second audio stage. From the dropdown menus along the top left of
the Power SDR interface, select “Equalizer” and position it on your
desktop so that you can access the Transmit Equalizer easily. I would
suggest that you enable the 10 band equalizer function at this time, if
you have not already done so.
7. Observe the TX meter “EQ” level as you speak into the microphone and
adjust the “Preamp” slider in the EQ interface so that your maximum
peaks reach no more than –2 dBm.
8. Set the TX meter to Leveler. Open up the PSDR tab for DSP and go to
the AGC/ALC settings page. As you transmit and speak into the mic,
adjust the “Leveler” setting upward or downward from the default setting
of 5 but make sure that peaks on the TX meter do not exceed 0 dBm. You
can further adjust the attack/decay/hang times if the Leveler is not
responding quickly enough, or if it seems slow to release. This is
largely trial and error, but I found the default decay and hang times to
be too long, and reducing them smoothed things so that there was no
audible pumping or excessive periods of gain reduction. (Pages 156 - 157
of the PowerSDR 2.x manual provide more details)
9. Set the TX meter to ALC. Open up the PSDR tab for DSP and go to the
AGC/ALC settings page. Apply audio and observe that the maximum level of
peaks does not exceed 0 dBm. If everything in the preceding stages has
been set correctly, you should see that your maximum peaks will end up
between -5 dBm and -1 dBm. You can also adjust the attack/decay/hang
times of the ALC if you see a peak sneaking through now and then. Again,
I found that by reducing the decay and hang times in small steps I could
find a setting that resulted in smooth audio without pumping or extended
periods of gain reduction. If your ALC levels are exceeding 0 dBm on any
peaks, reduce your “Mic” level by using the slider on the Power SDR
front panel GUI.
10. When you have finished, your audio should sound smooth and clean. If
your transmitted frequency response is not to your liking, the 10 band
TX equalizer built into Power SDR works very well and is more than
capable of making up for deficiencies in whatever microphone you have
selected. Always remember that after you EQ your audio, you should go
back through the steps to compensate for any changes in gain.
11. When you get all done with your adjustments, don’t forget to save
them in your TX profile! Each TX profile saves its own bandwidth filter
settings, front panel Mic setting, DX-Compander setting, EQ preamp level
with either the 3 or 10 band adjustments, Leveler setting, AGC/ALC
attack and decay, and RF transmit level. If you don’t save them, they
will be instantly lost when you switch TX profiles!
Summary: When your levels are set correctly throughout the audio chain,
engaging reasonable levels of the Compander or the DX function should
result in a very significant loudness difference in your signal, without
invoking the ALC or producing any signs of ringing or distortion. It's
possible to produce very clean and beautifully balanced audio with the
Flex and as long as the gain is set correctly at each stage, it should
sound smooth and natural.
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