Audio Musings: RX Streams, RX Gain and the Meter in DAX; Sampling Rates

Kev.  Depending upon the waveform, you may want to stay a notch or two below the "0."

I think Tim said something like "grazing the red once in a while is OK...having it bump it regularly or letting it stay there for a long period of time is bad..."  (My paraphrase.)

Making sure your sampling rate is evenly divisible into 48000 is good.  DAX installs already set to 48000.
Most Digi programs are set to even numbers... 8000, 12000, 24000, so that is fine.

RE:  AGC-T ... In very weak signal modes, I will sometimes use OFF and set it so that very strong signals do not drive the receive audio into distortion.  As long as it is clean audio, and enough for the decoder to function, the Digi programs have a lot of dynamic range and you don't really need to ride the gain control.... If the volume is too loud for your human ears, turn the local speaker volume down. In fact, if you keep riding the gain in the JT modes, you will always be cutting the weak ones out of the picture.

In other digi modes, like rtty, or FT8, I use FAST and set the gain just a little higher than the "Knee" or Sweet Spot.  I haven't noticed any great reduction of signal decoding.  Others may have different advice.

Note - using DigiU is the standard for most Digi modes.  It disengages the PROC and TX EQ in order to keep your TX audio cleaner for Digi.  Do not use USB or LSB for Digi modes.  The PROC can wreck havoc on Digi signals, as can the TX EQ.

RE:  Mic gain in Voice modes... Just for fun, have a look at my Youtube video on "A tour of my audio profiles."
it needs a little update, but in about the last quarter, I talk about "How to make a Flex sound BAD."

You can, if you are boosting the Bass frequencies significantly and using the Processor, overdrive the processing stage and sound really bad, even if you are not bumping the audio control into the red.

Some of my friends in broadcasting used to use a phrase to describe the effect of Hyper Bass Boost.  The anatomical reference translates roughly to "Giving you ....Gravitas"  or "Boosting your Testosterone Production."

I have found that when guys do this on SSB, it creates a strong "droning" carrier at a frequency between 60-150 Hz that is really irritating to listen to.  It also tends to overdrive the Processor and/or create artifacts in the audio chain that show up as distortion.

If using the PROC at more than NORM, it is usually advisable to bring your Lo Cut up to 150-300, and drop the TQ EQ below 250 Hz so that you don't overload the PROC or other mic circuits.  (if you are cutting everything below 300 Hz, it makes no sense to send lots of 63, 125 & 250 energy to the mic circuits.)

The best thing to do, in any case, is set yourself up to monitor your own audio using 2 slices and FDX.  Transmit into the XVTR port, and listen with a good set of headphones, or record your own signal and play it back.  Make sure that you have your receiving slice bandwidth at least as wide as your transmit signal.

The best way to keep from "overthinking it" is to experiment with it in a safe mode.....listen to your own signal, and adjust the TX EQ sliders up and down, one at a time, until you learn to discern what effect each slider has on the quality of your audio when boosted or cut.

There is an excellent article on the Flex Website about this:

http://kc.flexradio.com/KnowledgebaseArticle50114.aspx

Let me know if you need any more help.

Ken - NM9P

Here's a couple of screenshots showing what signals look like after a few hours of running fldigi and then again after I restart fldigi. Nothing else was done other than the restart of the application (and the fldigi-dxlabs-gw).

This is what things looked like this morning (looks bad):


Here's close to the same time on SSDR (looks good):


And here's what it looks like after restarting fldigi (looks good):


Not sure the problem is with fldigi. I haven't tried this yet with WinWarbler. WSJT-X and JTDX don't seem to have this issue but the signals are quite a bit different so I'm not so sure I'd notice. According to the FLDIGI documents, it seems to prefer the native sound card sample rate of 44.1 KHz but has settings for other sample rates. I'm running at 48 KHz as suggested by Flex. I'll keep poking the fldigi group list but if anyone else has seen this behavior I'd like to hear about it.

73,
Kev K4VD