Rob This is great stuff, Thanks.
I'm not clear on where VAC comes into the audio chain and which of these adjustments would impact VAC audio input. Per a prior knowledge base article, I've just been setting the drive to 100, the meter to ALC and adjusting the TX Gain for a -3 reading. Any advice on other adjustments for VAC/Digital ? Dave W0DHB -----Original Message----- From: flexradio-boun...@flex-radio.biz [mailto:flexradio-boun...@flex-radio.biz] On Behalf Of W1AEX - Rob Sent: Tuesday, May 10, 2011 1:17 PM To: flexradio@flex-radio.biz Subject: Re: [Flexradio] TX Audio Chain 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 ------------------ Audio Gain Distribution Inside PowerSDR: I have encountered lots of Flex/SDR users on the air who sound great in every voice mode. However, its 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. Its 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 dont 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, dont 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 dont 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. _______________________________________________ FlexRadio Systems Mailing List FlexRadio@flex-radio.biz http://mail.flex-radio.biz/mailman/listinfo/flexradio_flex-radio.biz Archives: http://www.mail-archive.com/flexradio%40flex-radio.biz/ Knowledge Base: http://kc.flexradio.com/ Homepage: http://www.flexradio.com/ _______________________________________________ FlexRadio Systems Mailing List FlexRadio@flex-radio.biz http://mail.flex-radio.biz/mailman/listinfo/flexradio_flex-radio.biz Archives: http://www.mail-archive.com/flexradio%40flex-radio.biz/ Knowledge Base: http://kc.flexradio.com/ Homepage: http://www.flexradio.com/
