San Diego City [800 MHz] "rumble"

[Alain]

Hello All,

I've just added the City's 800 MHz to my favorites list [on my SDS200] and, with ear buds. there is a quite noticeable, bassy, audio rumble in the background. It's also noticeable w/o the buds from speakers too. I made an extension cord in order to use the buds.

It's been a while since I monitored 800 MHz and was wondering if anyone knew what that phenomenon might be.

Many thanks as always!

 

[inigo88]

I believe you’re hearing the analog Motorola subaudible data. Since it’s below the audible range of your hearing (low frequency below about 300 hz), you normally don’t notice it. However bassy earbuds tend to amplify it enough to be heard underneath the analog audio. Try listening to analog Motorola trunking voice, LTR trunking and analog conventional channels with CTCSS or DCS tones all on headphones. All will have subaudible data that sounds like there is a bassy warble in the background, and the warble will change speed depending on the data rate.

 

[Alain]

inigo88...that is quite possibly the best description that I have received to date... ;->

Thank you for taking the time to reply!

 

[inigo88]

Glad to help!

 

[speedway_navigator]

It would be interesting to record the audio and pass it through a high pass filter at 300 Hz, easy to do in Audacity.

https://www.audacityteam.org/download/

That filter should remove the low frequency rumble.
Even though CTCSS tones are called sub-audible you should be able to hear the range from 67.0 to 254.1 Hz.

 

[Anderegg]

It's always been there, always on analog simulcast systems...the reason you notice it so much on the Uniden, is the HP and SDS scanners have added "BASS BOOST!", which really makes that noticable. My guess is they think bassy audio sounds more expensive than tinny audio?

On my PC, I use Equalizer APO to high cut and low cut sounds outside of 300-2000Hz...I also throw specific filters to kill specific CTCSS tones, such as the low hum you can hear on CHP low band.

Paul