how to pull Audio from TV Signal

[yllawwally]

How difficult would it be to modify or at least separate the audio portion of a tv signal, into a signal appropriate for headphones.

 

[crutschow]

SD or HD video?

 

[yllawwally]

NTSC SD video signal.

 

[Nigel Goodwin]

NTSC SD video signal.

There's no audio on a video signal - do you mean an analogue broadcast transmission?.

 

[crutschow]

For an NTSC SD broadcast signal you could use the tuner in a VCR. That gives a line-out audio signal which would have to go to a small audio amp to power the headphones.

Years ago they made small portable radios that would pick up the audio from TV broadcasts but don't think they're available anymore.

 

[yllawwally]

Would getting the audio be as simple as getting a FM receiver tuned to 65.75MHz for Channel 3 for example?

 

[yllawwally]

I'm trying to make a karaoke type circuit. However I want to mix my new audio on top of the audio for channel 3, then have it be on channel 3, on a regular tv, and have the output also on a set of headphones.

 

[kchriste]

Would getting the audio be as simple as getting a FM receiver tuned to 65.75MHz for Channel 3 for example?

Yes it would. Note that the TV FM audio signal is a lower bandwidth than standard 88-108Mhz FM, so it will be heard at a lower volume on such a receiver if it could be tuned that low.

 

[audioguru]

Yes it would. Note that the TV FM audio signal is a lower bandwidth than standard 88-108Mhz FM, so it will be heard at a lower volume on such a receiver if it could be tuned that low.

No.
TV audio is the same bandwidth and level as most FM Radio station broadcasts. They both have baseband sound from 50Hz to 15kHz plus the 19khz pilot carrier and the 23kHz to 53kHz stereo subcarrier sidebands. In North America they both have a max deviation of 75kHz.

 

[mneary]

Actually, the BTSC TV audio pilot is (was?) locked to the (approximately 15.734kHz) horizontal frequency.

 

[audioguru]

The video is AM modulated. The audio is FM modulated and has nothing to do with the video.

 

[mneary]

The TV stereo pilot is 15.734 kHz. Look it up.

 

[audioguru]

I couldn't find spec's nor a tutorial about TV stereo details but I found encoders and decoders.

I was wrong. The TV stereo pilot tone is at the video horizontal scanning frequency at 15,734Hz. A lowpass filter removes it so it does not beat with the high audio frequencies and so it is not heard. The audio rolls off at 12kHz to 14kHz.

The TV stereo multiplexing has a suppressed 31,468Hz frequency.

 

[Nigel Goodwin]

I couldn't find spec's nor a tutorial about TV stereo details but I found encoders and decoders.

It's country dependent anyway - the UK dismissed the USA scheme as too poor, and invented it's own NICAM system (Near Instantaneous Companded Analogue Multiplex) - a far higher quality system, completely separate to the mono sound.

But aren't we missing the point here?, I thought the USA had turned off analogue?, and gone entirely digital? - the UK is still in the process (doing it region by region over a number of years - 2011 for me).

 

[mneary]

The US has turned off all analog except for a few low power stations and repeaters serving remote areas. But some set top adapters create BTSC stereo for the old stereo TVs.

In Canada the digital transition is slowly getting under way. I think the deadline is late 2011?

 

[Nigel Goodwin]

The US has turned off all analog except for a few low power stations and repeaters serving remote areas. But some set top adapters create BTSC stereo for the old stereo TVs.

No NICAM modulators here - for stereo from VCR's etc. you use a SCART lead.

In Canada the digital transition is slowly getting under way. I think the deadline is late 2011?

The UK were the first to introduce digital terrestrial, it's been about for many years - but DSO (Digital Switch Over) wasn't allowed to be started until 65% of the population already had access to digital TV, and then the switch off started, phased over four years or so. There aren't going to be any analogue stations left when it's completed.

 

[yllawwally]

Most cable companies in the US still offer some analogue channels. I also get a few over the air channels.

 

[Hero999]

No NICAM modulators here - for stereo from VCR's etc. you use a SCART lead.

Older TVs don't have a SCART lead so VCRs used to have small modulators to connect to the TV.

Indeed with an aerial it was possible to broadcast the signal for a few meters. I remember sticking a small piece of wire into the RF jack of an old games condole and was able to transmit the picture across the room.

Of course this was of no practical use unless you just didn't have a long enough coaxial cable.

 

[audioguru]

My TVs are analog and my cable TV company converts the digital transmissions to analog for them.
People in the US were given coupons to be applied toward the purchase of a converter.