HD1 required?

[Scott Fybush]

On 6/15/2012 9:23 AM, Jim Hall wrote:
> I was wondering..are FM stations broadcasting in HD *required* to run an HD1
> service that duplicates the analog programming? For example, WEEI-FM, WTKK,
> and WBZ-FM all run "spoken word" formats on their analog signals which are
> not improved in clarity that greatly in HD. So, could WTKK, for example, run
> its talk programming only on analog, skip HD1 duplicating the analog, keep
> HD2 as Irish music, and then run additional HD sub-channels with additional
> programming? Not running the HD1 would give them more bandwidth for a
> high-clarity HD3 if they wanted to run another music program there. Often
> HD3's are used for spoken word because there is not as much bandwidth
> available.
>

There is no technical reason why you have to have an HD1 that duplicates 
the analog, but there *is* a regulatory requirement to do so.

However...you can divide the 96 kbps of primary HD bandwidth in whatever 
way makes sense, so if WTKK wanted to do so, it could allocate 32k to 
HD1 and 64k to HD2.

(As for HD3 - it's often forgotten that there's a newer version of the 
HD encoding scheme that provides for an additional set of carriers 
closer to the center frequency of the channel. That additional bandwidth 
- I want to say it's 32 kbps, but it might be 40 or 48k - can't be 
combined with the primary carriers, but it can be used for an HD3 and/or 
and HD4 to free up space for more HD1/HD2 bandwidth on the primary 
carriers.)

It's also not always the case that spoken word = lower bandwidth 
requirements. The codecs used for HD Radio are quite efficient for 
music, but often not so good for spoken word. I've heard a lot of 32k 
and even some 48k spoken-word HD services that are nearly unlistenable, 
and some 24k music services that are surprisingly adequate. Good 
processing makes a world of difference.

s