Setup Guide for the OpenHPSDR mRX PS (v3.4.1 and later) CFC Audio Tools

Initial Settings:  To start, go through the levels of the basic audio chain components to assure that they are set optimally. The steps below will help you to establish a good starting point:

1. With the TX multimeter set for MIC, select your source (Mic in, Line in, or VAC) and then set the audio level so your voice peaks are regularly reaching close to 0 dB. Note that if you are using a dynamic microphone you may need to enable the “20 dB Mic Boost” option located on the "Transmit" tab of the menu.

2. With the TX multimeter set for EQ, open the Equalizer menu at the top of the GUI console and select the "10-Band Equalizer" option. Note that you can customize the frequency point for each EQ slider but it is suggested that you try the default values initially. Adjust the equalizer sliders so that your audio source produces a relatively flat response with no over-emphasis in any part of your voice. Dynamic microphones tend to have a heavy low-end and electrets can be overly bright so each type typically needs to be treated differently. When you have flattened out the response of your audio source so there is no obvious over-emphasis, set the EQ Preamp slider so your voice peaks are regularly reaching close to but not exceeding 0 dB.

3. With the TX multimeter set for LEVELER, adjust the Leveler’s Max Gain setting so your voice peaks are regularly reaching 0 dB.

4. With the TX multimeter set for ALC, check to make sure your voice peaks are reaching 0 dB. If necessary, adjust the LEVELER so that your voice peaks regularly hit 0 dB. Note that this is essential for the Pure Signal algorithm to operate properly.

5. In the Transmit tab set your Transmit Filter to the desired bandwidth and then save your settings to a Transmit Profile.


CFC Introduction: The CFC (Continuous Frequency Compression) components include the PRE-EQ, CFC, POST-EQ, and the PHASE ROTATOR. Note that all of the CFC settings are stored within each TX profile they are saved in, to allow unique settings for each TX profile that you create. The steps below are suggestions for establishing a starting point to allow you to use the components to optimize your transmit audio. To start out, if you have COMP enabled in the Console GUI, disable it for now. (Note that you may elect to enable that later if you wish to add a “hard limiting” wideband compression effect to your transmit profile. Enabling CESSB will significantly raise your average power output and further accentuate the hard limiting effect when COMP is enabled.) Also, if Pure Signal is enabled, temporarily disable it so that the audio you hear with MON enabled is not pre-distorted.

1. PRE-EQ: In step 2 of the basic audio chain adjustments above, you set the EQ sliders to produce a relatively flat response for the microphone or audio rack that you are using and have set the Preamp slider so that you do not exceed 0 dB on voice peaks while monitoring the EQ with the TX multimeter. Note that when the CFC option is enabled, the basic EQ will function as the Pre-EQ stage. If you are satisfied that your settings produce a relatively flat audio response, you can move on to the next step.

2. CONTINUOUS FREQUENCY COMPRESSOR: In the DSP menu tab select the CFC tab and place a check in the “CFC Enable” and “Post-CFC EQ Enable” boxes. The CFC interface offers an over-all gain slider called PRE-COMP and 10 individual sliders that allow you to assign different levels of compression to each assigned frequency point. Note that in the image below you can see that the frequency points are optimized for a 3K wide SSB profile. While listening to your transmit audio with MON enabled, adjust the frequency band sliders upward or downward to control the amount of “punch” you wish to add to your voice in each area of the voice spectrum. When you have established settings that produce the desired level of density for your voice, you can change the over-all compression level by adjusting the PRE-COMP slider upward or downward.

3. POST-EQ: While listening to your transmitted signal with MON enabled, use the Post-EQ form to tailor your transmit audio’s frequency response. As you can see in the image above, the Post-EQ sliders are lifting the area from 1750 Hz to the upper edge of the transmit filter at 3070 Hz to add some brightness to the transmitted audio. The Post-EQ sliders give you complete control over the tonal quality of your signal to enhance clarity, brightness, and low-end response as desired. After adjusting your sliders, set your TX multimeter to CFC and than as a starting point, adjust the PRE-COMP slider so that you are reaching a compression level around 0 dB as you speak. Note that it's perfectly fine to exceed a level of 0 dB but you may wish to work with the balance between the PRE-COMP and POST EQ GAIN settings as described below.


4. Final Adjustments: The new “CFC Comp” meter shown in the screenshot below displays peak compression levels that exceed 0dB on a meter scale from 0dB to +25dB. This can be a very helpful reference to view as you set the compression level of the CFC components and then adjust the over-all gain of your transmit profile with the POST EQ GAIN slider. Remember that the PRE-COMP slider affects the over-all compression of the CFC components, and the POST EQ GAIN slider adjusts the overall audio level produced at this point in the transmit audio chain. If you plan to run fairly a light amount of compression the CFC meter would probably be the most useful to use for setting your desired compression level. If you prefer heavier compression that drives the CFC beyond 0 dB it may be more useful to monitor the compression level with the CFC Comp  meter.

The two new CFC meters give a nice visual indication of what is happening as you set the balance between the two CFC gain sliders. Note that by increasing the PRE-COMP gain slider and decreasing the POST EQ GAIN slider you will create more punch and loudness in areas of your audio that you have emphasized with your CFC slider settings. As the PRE-COMP slider is advanced you will see the peak compression level of the multiband compressor increase in the “CFC Comp” meter. For a less aggressive sounding profile, reduce the PRE-COMP slider until the “CFC” meter deflects to 0dB or less on voice peaks and then use the POST EQ GAIN slider to make up the difference in over-all gain to assure that you are driving the ALC hard enough to reach 0 dB while monitoring the ALC meter.

For those who wish to enable the console COMP button and CESSB, excessive output from the CFC components may make your transmitted audio sound somewhat harsh. To minimize this, try reducing the PRE-COMP slider so that the “CFC” meter displays maximum peaks of 0 dB or less. Note that when COMP and CESSB are enabled, the output is hard-limited at 0 dB as shown with the “ALC Comp” meter. A new adjustment for COMP and CESSB users is available that allows you to exceed 0 dB of ALC compression with COMP and CESSB enabled, to make it possible to use the look-ahead algorithm at the ALC level to incorporate soft-limiting in the final stage. You can try this new feature by moving to the DSP menu tab and then the AGC/ALC menu and using the new ALC “Max Gain” setting. Set the TX multimeter to view
ALC Comp and as you speak, you can increase the ALC compression in 1 dB steps from 0 dB to 10 dB. Several dB of “ALC Comp” should increase your over-all loudness without added harshness.

ALC Max Gain

5. REMEMBER to save your TX profile
:  When you are satisfied with your CFC settings, go back to the Transmit menu tab and save your profile.

If the directions above seem confusing, the YouTube video below may make things a bit clearer. Note that this is a 720p HD video so if you watch it at YouTube it should look sharp and clear when viewed in theater mode or at full screen.

Adjusting the transmit audio gain levels and the CFC Audio Tools

6. PHASE ROTATOR: This feature can be used to improve the symmetry of your voice in your transmitted audio. It’s a very individual adjustment as everyone’s voice has very different symmetry characteristics. The steps below will get you started:

• Set the Panadapter in OpenHPSDR to display the Scope.
• Select a transmit profile that has a fairly wide response and set the mode to LSB or USB.
• While transmitting, enable the phase rotator, and as you speak observe your voice pattern on the Scope display.
• If your voice has more energy above the horizontal zero axis reduce the number of stages until better symmetry is observed.
• If your voice has more energy below the horizontal zero axis increase the number of stages until better symmetry is observed.
• Try setting the FREQ of the Phase Rotator to something other than 338 Hz if you believe most of the energy in your voice is higher or lower.
• When you have found a setting that is symmetrical with similar energy above and below the horizontal zero axis, save your TX profile.

If the directions above seem confusing, the short YouTube video below may make things a bit clearer.

Adjusting the Phase Rotator

7. A few last thoughts:  Note that these CFC adjustment steps should be considered a starting point for optimizing your transmitted audio. When you have become comfortable with the interface, you might wish to experiment with changing the frequency points for the CFC sliders so they span the transmitted bandwidth of each transmit profile you are working on. As an example, for a 3.0k SSB profile try the following values:  50, 150, 300, 500, 750, 1250, 1750, 2300, 2800, 3000. There’s nothing magical about those numbers so experiment with values that give you the best tonal control for your intended bandwidth.

frequency points

The CFC Audio Tools will provide you with an impressive amount of control over the transmit audio your station produces. Also, keep in mind that if you are more comfortable with the traditional transmit audio adjustments in OpenHPSDR, they are still there!

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