They are several HD channels by a specific provider, they are part of the HD pack. Check at
www.voom.com/
To clarify a bit more.
1) The Voom channels were originally part of the Voom satellite service, now defunct
2) Majority owned by Rainbow Media. Subsidary company of Cablevision. Dish ended up being offered a percentage (20%?) when they agreed to offer the service on DISH with 10 of the original Voom Channels. This was at a time when there was a family fued between the Dolan's. Dish had already agreed to purchase voom's satellite and uplink facilities. The carriage deal was seperate but ended the opposition of the senior Dolan to the sale of the satellite.
3) When Dish started offering 10 of the Voom channels it was for $5 more and I believe you had to have the older Dish HD offering that was $10. These channels may not exactly match what Voom previously offered, and some have changed over time. E.g Guys and Majestic were later switched to Kung Fu and Film Fest. You originally had to have, or add, a dish that pointed at 61.5 the location of the Voom satellite Rainbow 1 that Dish was in the process of purchasing.
4) Dish launched a new HD package for $20 dollars that included all the channels in their older HD package and their Voom package, plus several other HD channels and 5 more Voom channels about a year and a half ago. The new channels were only made available to there new MPEG4 receivers. Some were really mpeg4 and some not when first offered. I believe all the added stations are now MPEG4, but someone else might be able to verify. They soon discontinued offering the older HD package and voom package to those not already subscribed.
5) The first 10 Voom channels that Dish carried are still MPEG2. They play to convert these 10 to Mpeg4 August 15. Obviously the older voom package is esentially being discontined.
Of the 32 Nationally offered HD channels Dish offers, 15 are Voom. The $20 fee is really an enabling fee. For most of the HD offerings you must have a package with equivalen offerings. For National Geographic HD you must have the AT250 package that offers National Geographic HD. etc. Similarly you must have the equivalent movie package for HBO HD, Showtime HD or Starz HD. Local HD and RSN hd (select game broadcasts) are available. More HD is about to be offered, notably 6 in August and 1 more September 1.