Audio recordings of radio traffic

[Stephen Tashi]

Audio recordings of radio traffic from famous incidents (e.g. 9/11, various shootings) are difficult to understand - at least those I find on YouTube are. Is there something about the way radio traffic is recorded that degrades it? Often the beginning of a sentence is cut off. Could this be a result of the delay in a recording device that tries to begin recording only after it detects sounds?

 

[jedishrfu]

Could be due to the speaker speaking before they pressed the transmit button because they were hurried or because the sound detection needed a second to turn on.

There's a 2 second wait after pressing the PTT button according to the protocol:

https://www.csudh.edu/Assets/csudh-sites/dhpd/emergency-preparedness/two way radio protocol.pdf

They mention that the 2 to 3 second delay before talking is needed for the tranmitter to become active.

 

[Bystander]

See "Squelch."

 

[berkeman]

Often the beginning of a sentence is cut off.

Many public service radio systems are "trunked", and that means that the transmitter and relay system need to agree on the TX/RX frequencies before information can be transferred. When you push the PTT button on a trunked radio, you need to wait for the "beep" (usually takes a second or two) to let you know that your connection is established. In the heat of the moment in an emergency, it's easy to forget to wait for the beep...

https://en.wikipedia.org/wiki/Trunked_radio_system

 

[Stephen Tashi]

The reason that I think the sound quality is due to the recording system and not the original sound is that in most recordings of radio traffic the people speaking seem to have no problem understanding each other. For example 3:32 to 3:42 in

 

[hutchphd]

First we should all listen to this recording every day for self evident reasons. That being said

The reason that I think the sound quality is due to the recording system and not the original sound is that in most recordings of radio traffic the people speaking seem to have no problem understanding each other.

The means by which these folks are talking to each other is local whereas the recording is presumably done at dispatch some further distance away. That would account for some of the degradation (particularly regarding acquisition delay) for the dispatch recording because of less signal strength. .I'm just guessing.

 

[Stephen Tashi]

The means by which these folks are talking to each other is local whereas the recording is presumably done at dispatch some further distance away. That would account for some of the degradation (particularly regarding acquisition delay) for the dispatch recording because of less signal strength. .I'm just guessing.

I'll guess that your are correct. But what is it about signal strength that results in the type of degradation where only parts of the transmission are inaudible? - something to do with digital communication and how things are transmitted in discrete packets? (I suppose there are recordings of pre-digital radio traffic, but I haven't encountered any in my recent YouTube browsing.)