Stereo on HD3!

[mgpt6]

It is harder to hold lock on HD-3 Compared to HD-2. Freeform BCN on WZLX -FM Boston is an excellent station. IS WZLX still at -20 db digital power and does CBS have plans to go to -14 or -10 db digital power?

WGBH -FM HD-2 in Boston carries the WCRB Classical music service. Much less than hiss than on 99.5 FM analog. Think GBH is -20 digital power but analog ERP is 97kW.Know they cant go -10 db digital but maybe -17 or 14 db digital power.

 

[jhardis]

It is harder to hold lock on HD-3 Compared to HD-2.

It's exactly the same. All HD streams are multiplexed into the same data channel.

- Jonathan

 

[satech]

It's exactly the same. All HD streams are multiplexed into the same data channel.

Yes, except that lower bitrate HD streams (as HD3 typically is) have less leeway when it comes to the receiver's error correction that kicks in when the digital data starts dropping out, so a low-bitrate HD3 stream is more likely to cut out, while a higher-bitrate stream might sound garbled for a while during the error correction but keeps playing.

 

[Ai4i]

It is harder to hold lock on HD-3 Compared to HD-2.

It's exactly the same. All HD streams are multiplexed into the same data channel.
- Jonathan

I thought the same as Jon, until I had trouble locking onto a local HD-3 and spoke with an engineer from the local (West Palm Beach) CBS cluster who explained it to me this way:
The HD-1 information is farthest from certain analog sidebands, then the HD-2, then the HD-3.
There is a way to resolve the issue (something called extended or expanded something-or-other) but it comes at a price:
If the station is set up to avoid the issue of interference from analog sidebands, some digital bandwidth is lost.

 

[jhardis]

It is harder to hold lock on HD-3 Compared to HD-2.

It's exactly the same. All HD streams are multiplexed into the same data channel.

I thought the same as Jon, until I had trouble locking onto a local HD-3 and spoke with an engineer from the local (West Palm Beach) CBS cluster who explained it to me this way:
The HD-1 information is farthest from certain analog sidebands, then the HD-2, then the HD-3.
There is a way to resolve the issue (something called extended or expanded something-or-other) but it comes at a price:
If the station is set up to avoid the issue of interference from analog sidebands, some digital bandwidth is lost.

Okay, I looked it up...

There are four relevant data channels:

P1 -- 98 kbit/s, always present
P2 -- not presently used; will be used only in all-digital mode
P3 -- 12 kbit/s or 25 kbit/s, the first two increments of "extended hybrid" mode, if used
P4 -- 25 kbit/s, the third (last) increment of "extended hybrid" mode, if used

The Main Program Service (HD-1) is always found on the P1 channel.

The Supplemental Program Services (HD-2, HD-3, ...) can be put on any of the three channels. Furthermore, they can be split into "core" and "enhanced" data streams (where "enhanced" can contain the stereo separation information), with each part using a different data channel. Examples of ways of splitting things up can be found in Table 5-1 of document 1014s in NRSC-5. For example, one can put HD-1, HD-2, and HD-3 core on P1, and HD-3 enhanced on P3. Or, one can put HD-1 and HD-2 in P1, and all of HD-3 in P3.

All program streams on the same data channel are multiplexed together and suffer the same fate. However, for a variety of reasons (including spectral isolation and different levels of error correction), P1 is more "robust" than P3 and P4. (See Section 7.2.4 in document 1011s of NRSC-5.) It is possible to have good reception on P1 but poor reception on P3 or P4.

So, the correct answer seems to be that it depends on how the broadcast station is configured.

- Jonathan

 

[Ai4i]

That is a much better explanation

"extended hybrid" mode,
the correct answer seems to be that it depends on how the broadcast station is configured.
- Jonathan

A much better explanation than what the CBS guy told me.
So, if part of a channel is on P1 and part is on P3 or P4 (maybe the L-R), will it have the stability of P1 or the instability of 3 or 4? Would the main channel be solid but the separation be less solid (go in and out of stereo)?
Full digital should resolve many of these issues.

 

[jhardis]

So, if part of a channel is on P1 and part is on P3 or P4 (maybe the L-R), will it have the stability of P1 or the instability of 3 or 4?
Would the main channel be solid but the separation be less solid (go in and out of stereo)?

The "core" stream would have the robustness of P1, while the "enhanced" stream would have the lower robustness of P3/P4. This is the way the IBOC system is intended to work, particularly on AM: a graceful fade with the "enhanced" stream dropping out first and the remaining "core" stream still being serviceable (albeit with less stereo separation, frequency range, or whatever) under conditions of weaker reception.

- Jonathan