Radio sounds come out earlier than TV's

[bentzy]

When hearing the same sound coming out from a Radio and a TV simultaneously (e.g., when
a channel is beeing broadcasted on the radio and on TV at the same time), the radio sound
precedes the sound coming out of the TV. The phenomenon is quite noticeable. The reason
for this must be technological, and is likely due to different delay time/s through both machineries. I'd like to get more information about this delay and related phenomenon.
Thanks.

 

[tiny-tim]

Welcome to PF!

When hearing the same sound coming out from a Radio and a TV simultaneously (e.g., when
a channel is beeing broadcasted on the radio and on TV at the same time), the radio sound precedes the sound coming out of the TV. The phenomenon is quite noticeable …

Hi bentzy! Welcome to PF!

Is this UK or US? Digital or not?

If it's digital TV and ordinary radio, then the radio will be earlier because the digital signal gets delayed while it's encoded (and, no, I don't know why, but I do know that that happens ).

 

[bentzy]

Thanks a lot, for your greetings and reply, as well.
What's the difference between UK & US ? It is in Israel, and I think it's in the same
category as the UK (Europe).
Analog vs digital is a very good point.

Let's wait for a more profound answer to this.

 

[Hootenanny]

This may seem a little obvious, but are you sitting closer to the TV than the radio or visa versa?

 

[tiny-tim]

This may seem a little obvious, but are you sitting closer to the TV than the radio or visa versa?

​

oooh … and is the radio submerged in a lake, or other material with a faster speed of sound than air?

 

[bentzy]

Obvious but legitimate. In ambient conditions, our hearing sense cannot detect path differences of a few meters - it's on the order of magnitude of a hundredth of a second !
(The speed of sound is ~340 m/sec).
Anyway, it is to do with the electronics rather than the propagation of sound waves. The
phenomenon is prominent - about a whole sentence discrepancy between the sources.

 

[bentzy]

Then the difference will be further less detectable, since sound travels faster in denser media, e.g., ~3 times as much in water.

 

[mgb_phys]

Digital radio is delayed by at least a second as it is encoded, the data shipped to the transmitters and buffered. It became a problem when things like Radio 4 went digital because they carried time signals (the pips) and the chiming of Big Ben at the start of the news.

 

[Pumblechook]

Virtually all radio and some TV is distributed digitally. Depending on the type of digital transmission the delay will vary due to the encoding and decoding processes and any buffering (short term storage) in between.

 

[tiny-tim]

digital radio?

Virtually all radio and some TV is distributed digitally.

Hi Pumblechook!

Here in the UK, I think most people still listen to analogue radio.

I don't know about Israel, though.

 

[Pumblechook]

Whatever you are listening to.. Long Wave, FM, DAB . It is distributed digitally by a NICAM system (has been for about 20 years) unless that has be replaced with something else in recent years with a longer delay.

 

[berkeman]

Anyway, it is to do with the electronics rather than the propagation of sound waves. The
phenomenon is prominent - about a whole sentence discrepancy between the sources.

The signals are delayed on purpose by the broadcasters, and apparently they use different delays for TV and radio. This will vary by region, most likely.

One of the reasons for delaying live broadcasts is to have the producer ready to push the "mute" button to prevent profanity or other slips from going out over the air. For example, when you call into a radio talk show, you are told to turn down your radio, so that you do not get confused by hearing the discussion (and yourself!) coming back with the radio delay.

 

[tiny-tim]

Nicam

Whatever you are listening to.. Long Wave, FM, DAB . It is distributed digitally by a NICAM system (has been for about 20 years) unless that has be replaced with something else in recent years with a longer delay.

Doesn't NICAM stand for "near-instantaneous" … about a millisecond?

"Modern" digital radio and TV is delayed a lot longer than that.

 

[Pumblechook]

The delay is quite noticeable with NICAM. Lot of buffering maybe. I was a BBC engineer and presenters complained that when using off air cueing off FM transmitters they found it disorientating when listening to themselves on outside broadcasts.

DAB is delayed much more. And there can be different delays between different DAB receivers. I have two here with quite a noticeable delay one to t'other.

 

[mgb_phys]

Doesn't NICAM stand for "near-instantaneous" … about a millisecond?

That just means it is broadcast alongside the main mono channel (in it's original TV usage) - it doesn't say anything about how long it takes to encode it or send it to the transmitters.
Generally the studio-transmitter link for radio is much more direct and real time than video it used to be that radio went over leased lines and the video mostly over microwave links - although I might be a bit out of date.

Interesting aside - the BBC used to send the pips (time signal) slightly ahead of time to allow for the speed of light delay between the main long wave transmitter and London (100mi away) so that the pips arrived exactly on time. The difference of course is completely undetectable when compared to the audio delays in the radio + speaker - but it's one of those 'because we can' features that the BBC used to do when it was a world leader in broadcast engineering.

 

[Pumblechook]

Radio has been distributed by NICAM on microwave links from maybe the mid 80s. Previous to that Linear PCM on microwave links from the early seventies. Old fashioned lines (music circuits) were used (no idea of the present situation) to feed AM transmitters but usually they would provide relatively short links off the backbone of the PCM/NICAM system. Even the music circuits may have been (are) digital on part of the route.. We never know exactly what BT did as the long as the programme arrived loud and clear.

TV sound has been largely digital from the seventies... bits inserted in the video sync pulses or where the sync pulses would normally be ..Sound in Syncs..now two channel Sound in Syncs. The sync pulses being regenerated at the transmitter.

We must be boring folks with all this...

Basically delays are introduced with digital distribution and transmission of radio and TV.

 

[mgb_phys]

I did work on a study to use a peer-peer system for distributing content to the transmitters, the idea was to use lower bandwidth links and large local buffer disc arrays at the transmitters to save money and allow more distributed production centres.

I do rememebr that the BBC were very keen on keeping direct live links and direct control of the transmitters - this was always explained as 'security' but may have just been an old fashioned attitude. I think the transmission system is now outsourced anyway.

 

[Pumblechook]

I think all transmitters (BBC and the rest) are run by an Australian company now...

Arqiva

 

[russ_watters]

Note that this is also a problem when going between different transmission media for the same station. Ie, my parents don't have cable to every TV and there is a delay between cable and air for the same channels. Same goes for a bar that mixes cable and satellite.

 

[Pumblechook]

Different systems.. even different receivers..different delays and satellites introduce an additional delay because it takes about 1/4 a second for a signal to reach a satellite and come back down.

 

[bentzy]

Following the discussion so far, it seems to me that it is do with different delayes in analog vs digital devices (see Tiny-Tim's first reply & Pumblechook's last one, last sentence), basically, at least.
To sharpen the point, let me say that I encounter the phenomenon when the same news are broadcasted simultaneously on the radio by some channel, andby some TV channel that shares the broadcast. This implies that no intervention is relevant here, and only conversion processes might be involved.

Thanks for your participation in this discussion,
Bentzy.

 

[bentzy]

Let me update my previous reply:
a. I mean Pumblechook's #16.
b. Following russ_watters's reply: significant contribution originates from cable transmission
vs on the air. The speed of the electric signal propagating along the cables (waveguides) is
significantly reduced compared to the EM wave on the air (~30% lesser).

Best wishes.

 

[mgb_phys]

Yes to recap - all the perceivable delay is due to digital processing in the studio and delays in the data network to the transmitters. Some delay on satelite is due to the round trip time upto orbit and back. The speed of light propagation from studio to transmitter and transmitter to your radio is very small.
The amount of delay and which is first totally depends on the systems being used by the broadcaster and might even change during the day if different network routes are used.

The reason it is there is largely cost - there is no real market driver to have instant broadcasts. People who need accurate time signal have GPS and nobody else really cares if their live TV/Radio broadcast is 1-2 seconds late - except those who like to
watch cricket while listening to the commentary on the radio.