Canadian TV, Computing and Home Theatre Forums banner

Why is OTA DTV audio easily broken with weak signal?

5253 Views 17 Replies 12 Participants Last post by  Schmerpy
I use OTA HD, and sometimes I watch a weak channel. When the picture is even slightly garbled, the audio is intermittent. Why?

Audio is 448Kbps Video is 19200Kbps. It is 2.3% of the total amount of data for HD. So why is even a slight garble in video results in bad audio? I understand if bad reception causes me to lose say 10-20% of data, but what's the likelyhood that ALL of 2.3% of audio information is lost in there ALL THE TIME?

For analog OTA, the picture can be ridiculously fuzzy, and the audio would remain crystal clear.

I'm using a LG 50PK550, with the antenna plugged directly into the TV.
1 - 3 of 18 Posts
so NTSC was deliberately specified to use AM (Amplitude Modulation) for the video while the audio portion uses FM (Frequency Modulation).
Originally, prior to WW2, AM was also used for audio. It was later switched to FM to improve sound quality. This is the first time I've heard any mention of interference between audio & video being the reason for FM audio. There were interference issues that dictated the frequencies used for colour which also required a very slight change in sync frequencies. Also, with analog TV, there were often separate transmitters for audio & video, instead of combining both into one transmitter.
That would require a return signal.
Actually, no. There is also "forward error correction" where you provide sufficient redundant data so that the original can be recovered despite errors. That's what's used on CDs, DVDs etc. It's also used on space probes, where the long return trip precludes retransmission requests. This contrasts with error detection and retransmission, as used on computer networks. Also, I think you'll find the cable data return channel is for actual user data, not error correction.
The problem might be further back in the chain. On my A/V receiver, I can see when the audio feed fails (the various status lights turn off) over the cable. Sometimes I get audio drop outs that don't show on my receiver. This would mean the problem is likely somewhere ahead of the cable path to my home. In your example, the problem could be before the signal gets to the transmitter.
1 - 3 of 18 Posts
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.