How to Setup Virtual Audio Cable (VAC) 4.0x with PowerSDR 1.x ...

1. Obtain and install VAC 4.0x on the same computer that is running PowerSDR2. Configure VAC "cables"3. Configure PowerSDR to utilize VACStep 1. Install VAC 4.0x as per the installation directions. If VAC was previously loaded, you mustfirst uninstall all versions before installing a new version of VAC 4.0xStep 2. Once installed, set up a pair of VAC audio "cables" for use with PowerSDR by opening theVAC Control Panel.Figure 1 - VAC ConsoleStep 3. By default only one audio cable is defined. You will need to create two cables by changingthe driver parameters to 2 cables then click SET and Restart. Highlight the appropriate cable andchange the values to match the figure above. In the "Ms per int" box enter a value between 1 and20 ms. The lower the value, the smaller the VAC audio buffer. In the example above, 7 ms wasselected. Depending on your computer setup you may have to adjust this value to prevent theaudio from dropping out or "popping".You can choose two different Stream limit formats; cable format and cable range. SincePowerSDR defines both audio cables' format when VAC support is enabled, using the CableFormat is recommended. If you decide to use the Cable Range stream format, one thing toconsider, when a format conversion occurs, it takes significant CPU resources and it maynoticeably slow your applications causing audio drops outs. Therefore using Cable Format as thestream format may help with audio drop outs. In the example above, I am using Cable Rangebecause it provides the most flexibility and does not adversely affect the performance ofPowerSDR on the computer I am using.After completing all of the necessary changes, click on Set for each cable when completed.NOTE: Repeat these changes for the second audio cable as well.NOTE: Do NOT check the Volume Control box in the VAC control panel. This enables theWindows Mixer and can cause unpredictable results.Step 4. Start up PowerSDR version 1.6.0 (or higher). Click Setup on the Menu Bar. ThePowerSDR Setup program is displayed. See example below.Figure 2 - PowerSDR Setup (default page)Step 5. Click on the Audio tab and then click on the VAC tab.Figure 3 - VAC Setup

Step 6. In the "Virtual Audio Cable Setup" section, set the "Driver" to MME using the drop downbox (other driver options, such as Windows WDM-KS are supported but may work depending onthe sound card application being used. For this article, MME is used because it is the mostcompatible. Once you have VAC working, you can experiment with the other drivers. Theiradvantage is that they have less inherent latency for audio transfer). In the "Input" drop down box,select Virtual Cable 1. In the "Output" drop down box, select Virtual Cable 2. In the "AutoEnable" section, select this option if you want VAC to automatically engage when any of the digitalmodes (DIGIx or DRM) are selected on the PowerSDR console. This is the preferred setting. Inthe "Buffer Size" section, select a buffer size from the drop down box. Depending on yourcomputer setup you may have to adjust this value to prevent the audio from dropping out or"popping". In the "Sample Rate" section, select a higher sampling rate from the drop down boxoption that exceeds the sampling rate of the sound card program you are using. Using asampling rate of 48K provides the best audio quality and produces the fewest drop outs.Troubleshooting Technique: In some cases the sound card program can not handle formatdown conversion very well resulting in no or poor audio processing. If this is the case,change the Sample rate to exactly match that of the sound card program you are using.If the soundcard program uses a stereo mode, such as DReaM, then select the Stereo option inthe "Mono/Stereo" section. And finally, the "Gain (dB)" section is the place where you adjust theAF gain of the VAC cable. Since the Volume Control was not checked on the VAC Control Panel(step #3) the Windows Mixer is not available for VAC cables. Use only the adjustments inPowerSDR to increase or decrease the volume (AF gain) going to and from the sound cardapplication.NOTE: Always start PowerSDR with VAC enabled before starting the sound card programso that PowerSDR can define the VAC cable formatSetp 7. To check to see if VAC is properly working, Select a digital mode in PowerSDR and makesure the radio is "On" and not in "Stand By" mode. The Open the VAC Control panel and youshould see the audio cables active.Figure 4 - VAC Control PanelAs displayed above, the VAC channels are active, but only for PowerSDR. If you look at Cable 1,you will see that the number of "Pb streams" is 0 (zero) and the "Rc streams" for Cable 2 is also 0.VAC 4.0x automatically sets up both ends of the audio cable even if the client (sound card)program is not configured or even running.Step 8. When setting up VAC with two audio programs, the audio output of one program uses thesame audio cable as the input of the other. Conversely, the audio input of the first program usesthe same audio cable as the output of the other.

In your sound card program's setup for which sound card you are using, you will need to set thesound card input to "Virtual Cable 2" and the output to "Virtual Cable 1". Below is an example ofhow MixW is configured. Note that the sampling rate does not match what was setup inPowerSDR - This asymmetric configuration seems to provide the best audio quality and the fewestaudio drop outs.Figure 5 - MixW Sound Device SettingsStep 9. After you have the sound card program's audio input and output set, you should startobserving audio either by hearing it or watching it on a spectrum display such as a waterfall. Youcan verify the VAC channel for the client program is active by looking at the VAC control panel.Figure 6 - VAC Control Panel with MixW receivingNotice that the value in the RcStream for Cable 2 has changed for a 0 (zero) to a 1 (one). Thisindicates that cable 2, which is the input for MixW is actively receiving audio from PowerSDR.Note: The Pb Stream value for VAC audio cable 1 is still 0 (zero). This will not change to aone (1) until you are transmitting using the sound card program and MixW is sending audiothrough that cable.Figure 7 - VAC Control Panel with MixW TransmittingStep 10. At this point you have completed the set up of VAC 4.0x with a sound card program.This KB article may reference additional files that are available on the FlexRadio Systems web siteDownloads page. Please use the URL(s) below to download the referenced materials.An Adobe Acrobat Reader may be required to open the file. You can download Adobe Acrobatfrom here.KB Source Document(s):NoneReferencedLast Modified By: Administrator, Sunday, October 19, 2008http://kc.flex-radio.com/KnowledgebaseArticle50230.aspxFriday, September 11, 2009