SDR++ Waterfall Works but There Is No Audio

[Pavel]

Short answer: When SDR++ displays live spectrum, the hardware stream is already working. Silence is normally caused by the VFO not covering the signal, the wrong demodulator or bandwidth, closed squelch, muted VFO audio or the wrong audio sink.

Before you start​

• First prove that the operating system and the hardware vendor's basic utility can see the SDR. An application cannot fix a missing USB, network or driver layer.
• Record the exact application build and SDR driver or support-library version. Plug-ins and source modules are often coupled to a particular build or architecture.

Step-by-step method​

1. Step 1: Create or select a VFO and center its filter on a known signal. Confirm the VFO is enabled and that its volume is not muted independently from the main application volume.
2. Step 2: Choose the expected mode and filter: WFM around 150 to 200 kHz for broadcast FM, NFM around 10 to 15 kHz for narrow voice, or AM around 6 to 10 kHz for common AM voice tests.
3. Step 3: Move squelch below the current noise level so it remains open. If audio appears only then, set the threshold slightly above idle noise rather than at an arbitrary high value.
4. Step 4: Open the Sink or audio menu, select the physical output device and check the Windows volume mixer. Remove virtual audio routing until normal speaker output is proven.

Concrete example​

A strong local FM station provides a clean test: place the VFO on the peak, choose WFM, use about 180 kHz and open squelch. If the VFO audio meter moves but speakers remain silent, the issue is after demodulation in the sink or operating-system mixer.

How to judge the result​

Audio is fixed when the same saved VFO produces sound after restarting SDR++, without reopening squelch or changing Windows output each time. If no audio-level meter moves, continue checking VFO placement, mode and filter.

What to record​

• A clean software baseline can start and stop the device repeatedly for ten minutes without dropped samples or a device-busy error.
• Confirm the displayed center frequency, sample rate and audio device rather than assuming saved settings still match the current hardware.
• When testing a change, close other SDR programs so only one process owns the receiver.

Common mistakes​

• Changing several hardware, software or RF variables at once, which removes the controlled comparison needed to identify the cause.
• Treating one autoscaled screenshot or one unusually good result as proof without recording the settings and repeating the test.
• Increasing sample rate or RF gain does not solve an inactive VFO or wrong audio sink and can create a second overload problem.

Final check​

Restart the application and computer once, then repeat the exact software workflow. Keep the configuration only when the correct source, device and output return without hidden manual repairs.