Blaineh,

I am not sure what the actual bit rate is compared between the two, HD Radio vs. Sat. Radio. My experience with Sat. radio is only with Sirius which has a much better technology then does XM. However, I can say that the sound quality I get from my home receiver driven thru my 990 is quite good! In fact I would say that on some of the dedicated music channels the quality is approaching that of a standard CD. I have listened to HD radio but only in cars and I was less then impressed, granted that could be related to the quality of the car system as well.

Does anybody know what the true rates are for these two technologies? I did some research and found some information thru Wikipedia (which I don't always trust). The following is a quick summary of what they reported relative to the bit rates of the two technologies.

People should not be confused by the term HD Radio it really means Hybrid Digital Radio and not High Definition! In general for HD Radio braodcasting via an FM signal they are allowed around 300Kb/sec, not entirely clear what the exact number is, which to me seems rather strange. However this bandwidth would be for all the different programs that would be broadcast on that particular frequency. Therefore, it will be entirely upto the radio station to decide the the bit rate to be used on any given stream. But certainly there should be enough there for stereo CD quality or even multi-channel programing. However, please note that this bit rate will only be possible if and when the FCC allows a radio station to stop broadcasting its analog signal. So under the current restrictions they are not able to use anywhere near that 300Kb/sec bit rate. Although I could not find any information as to what rates they are using. Also, I could not find whether they are using any sort of compression algorithms, my guess is they are not.

Sirius Satellite obviously is using a radically different technology. First of all the available bandwidth is substantially higher. But granted that bandwidth must be shared among all of the different channels. However, the bandwidth is not shared evenly. In fact there is quite a bit of difference between the channels, i.e. talk shows and news channels get much less of the pipe while the music channels get quite a bit more. One of the ways they pack all of this into the pipe is by using Perceptual Audio Coder (PAC) which is a very good compression algorithm. Here is a short description from Wikipedia:


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Perceptual Audio Coder (PAC) is an algorithm, like MPEG's MP3 standard, used to compress digital audio by removing extraneous information not perceived by most people. It is used by Sirius Satellite Radio for their DARS service, and iBiquity has been testing it for their IBOC digital radio upgrade for FM and AM. PAC is very similar to Advanced Audio Coding, the latter sharing many design elements.

The PAC originally developed by Elemedia, a subsidiary of Bell Labs, has a flexible format and bitrate. It provides efficient compression of high-quality audio over a variety of formats from 16 kb/s for a monophonic channel to 1024 kb/s for a 5.1 format with four or six auxiliary audio channels, and provisions for an ancillary (fixed rate) and auxiliary (variable rate) side data channel. For stereo audio signals, it is claimed that it provides near compact disc (CD) quality at about 56-64 kb/s, with transparent coding at bit rates approaching 128 kb/s[citation needed]. In the 1993, ISO-MPEG-2 5-channel test, PAC demonstrated the best decoded audio signal quality available from any algorithm at 320 kb/s, far outperforming all algorithms, including the layer-II and layer-III backward compatible algorithms.[citation needed]

Over the years PAC has evolved considerably. A known software implementation of this codec is CelestialTech's AudioLib. Later, it was considerably improved and renamed to ePAC (enhanced Perceptual Audio Coder) by Lucent. It's available in the AudioVeda music library manager.

The non-capitalized term is used to describe lossy compression codecs that utilize perceptual coding techniques for audio.


As you can see the available bit rates are quite high. My only concern is that it appears that the PAC routine is a "lossy" type compression.

Now having looked at all of that I still come back to what does the side by side listening tests reveal. I have not been able to test it side by side on the same system so I can't answer the question. But it appears on paper that Sirius music channels should hold up quite well as compared to the HD Radio of today. Has anyone out there compared them side by side, what was your experience?