Audio quality using Audacity

[scan_madison]

I have Audacity set to 11025 Hz (Project Rate). Receiver is RTL-SDR V3 on core i5 laptop. Here's the snippet of the recording:
Tower Recording

I haven't tried with different Project rate yet. But any idea why there's whine in the recording? Could it be due to antenna? I am using a simple dipole. Thanks.

 

[FKimble]

I've used Audacity to record live over the air 2m nets and the recording is exactly what I hear from the radio/PC speakers. Did you hear the whine over your speakers. I usually copy to a CD so I use 44100 Project rate.

Frank KK4YTM

 

[bharvey2]

The whining frequency is different depending upon who is doing the talking. That seems strange. I'd think it would be consistent throughout the recording. Do you hear it when listening live?

 

[scan_madison]

44100 definitely seemed to help as suggested by FKimble. The only problem is compared to 11025, file size on 44100 is humongous.
bharvey2, no I don't hear the whine when listening live.

 

[bharvey2]

I'd expect 44100 to sound better but you're right, it will make the file size much larger. You might try changing the sampling format to 16 bit. I suspect you'll have to mess around with the sampling setting until you find a suitable set of preferences.

 

[FKimble]

Change to mono from stereo. That will cut size in half. There are 3 different rates between 11025 an 44100. Give them a try maybe.

Frank

 

[radioman2001]

It's possible you won't hear it live since the radio is using an audio low pass or band pass filter. You can try using a low pass filter to remove it in Audacity after you record it.
I use a 2175hz notch filter to review recordings that are taken directly from the RTL lines to the transmitter. That constant 2175hz keying tone can drive you crazy to listen to after a while.

 

[dem1]

Your recording sounds like RFI (Radio Frequency Interference) on your RTL-SDR's receive frequency, rather than a problem with Audacity. The pitch of the heterodyne (or whine) which you hear is the difference in frequency between the aircraft's transmit frequency and interfering signal. Each aircraft has a slightly different transmit frequency (hence the difference in pitch), and the interference is reduced when the signal from the aircraft is strong.

If the interference is locally generated (possibly coming from your own laptop), try locating your antenna as far away from the source as possible. I'd also recommend reducing your RTL-SDR's receive bandwidth. For AM, try experimenting with values in the 6000 - 8000 Hz range. Lower values will reduce audio fidelity but also reduce the amount of interference you hear. Choose a value that sounds best to your ears.