HD Radio questions

I am happy with FM HD Radio's sound comapred to analog, but I never did any critical comparison to any CDs. My local Rock "Deep Tracks" HD2 channel has a quite wide variety, but I have never had satellite radio to compare. I have not noticed songs blending in to each other, so there must be a quiet spot between them on the HD2 channels. There are various station announcements, but definitely far fewer than on the HD1 simulcasts of the analog content. Ultimately, though, I figure it is still free radio, not my CD collection, so I keep my expectations lower. That free versus paid distinction and accompanying expectations is the main thing that has stopped me from even considering buying into satellite radio.

It's the same with HD Radio subchannels; There is no overlap, but there is also no detectable dead air between songs (unless the song itself starts with a period of silence). Most of the content selection on HD subchannels is quite automated, and this applies almost universally to the text information events broadcasted along with the song (title, artist, etc.). IOW, the text information is typically synced precisely with the song change.

Software HD Radio receiver controllers like HD RadioPC can distinguish between different songs using this synced change along with other factors. You simply click the auto-record button and every song broadcasted is recorded as a separate mp3 file, with the title and artist used for file name and ID3 tag info.

There are only two HD Radio receivers currently available that can be controlled with a PC, the Directed DMHD-1000 and the Visteon Zoom HDZ300. Although they are both designed to be used in vehicles, there is a kit available that converts either receiver for use on a home or office PC.

Oh, we have had some arguments about that one. I'm on the side that says that, all other things being equal, the 96 kbps single-stream stations sound significantly better than any analog receiver, while lower bitrates sound significantly worse.

Others feel differently . . . . . . . . .

In any case, I suspect "near CD quality" (whatever the hell that is) is achievable in HD at 96 kbps, but it's always going to be at the mercy of the station's audio processing (as is your Polk).

Unfortunately, I have little hope that satellite radio will ever take steps to improve audio quality, since the satellite TV companies certainly base their whole business model on doing precisely the opposite.

Today, I was with a friend who has the JVC car HD Radio receiver and also has a satellite radio tuner attached to it. I got in his car and it was playing a song from the 60's. We have only one local oldies station, an HD2 channel. After a few seconds of the song, I asked him "This is the satellite oldies channel, not the HD2 one, right?" Yes, it was, and I could tell... It had that mechanical or tinny bit-starved sound to it, that I have not yet heard from any HD station, but that I recognized right away from poorly-encoded MP3 songs. The next couple of songs sounded better, though.

I am a longtime XM subscriber, and have yet to hear an HD music signal, multicast or not, in my area that doesn't sound significantly better than satellite radio. At all bitrates HD will have better channel separation, and a more "open" high frequency response than analog FM (due to lack of pre-emphasis/de-emphasis). But at 48kbps audible artifacts are not uncommon. To me, they are less bothersome than the higher noise/distortion, and more limited hf response of analog fm stereo. I believe it's a sound (when properly engineered) that most will find superior to analog fm stereo. At 96kbps, it is my belief that double-blind testing would show no audible artifacts from 96kbps HD, and that (taking processing into account) it would prove "transparent" when compared to cd. Your mileage may vary.

I think a lot of folks can get a bit confused when we talk bitrates as far as HD Radio is concerned. I have even encountered instances where someone mistook it as an equivalent to mp3 file bitrate. The two are not even close, as HD Radio uses a derivative of mpeg-4 high efficiency AAC V2 to compress audio data. The difference is more similar to the mpeg-4 technology that Satellite TV uses now to enable a "few hundred" more High Definition TV channels on the same ole pipe. Its still a lossy compression algorithm, but its selective lossy in that discarded data is primarily in the inaudible spectrum (way over inaudible for my old ears), and it incorporates technology like spectral band replication and parametric stereo.
Here is an interesting quote:

"Scientific testing by the European Broadcasting Union has indicated that HE-AAC at 48 kb/s was ranked as "Excellent" quality using the MUSHRA scale. MP3 in the same testing received a score less than half that of HE-AAC and was ranked "Poor" using the MUSHRA scale. Data from this testing also indicated that some individuals confused 48 kb/s HE-AAC encoded material with an uncompressed original." (that quote refers to HE-AAC v1, version 2 is a even better)

Near CD quality is a pretty conservative descriptor for HD Radio, since according to the mpeg-4 HE AAC V1 specification (ISO/IEC 14496-3, Amd.2:2004) actual CD quality is obtained at approx. 100 kbps. I am sure that the 96 kbps value employed by HD Radio factors in the V1 vs V2 differences. Considering that typical CD audio runs at over 1000 kbps uncompressed, I would say that its one hell of an impressive compression algorithm.

If we can dump analog radio entirely and switch to digital only, there appears to be quite a treat in store for us. I would certainly enjoy the CD quality digital surround sound emitted from my little HD Radio receiver if that ever transpires.

With the help of a local FM station we tried the following. Using Goucho SACD stereo disk and several DCC gold disks mastered by Steve Hoffman, we made sure all eq and signal processing, other than the limiter were turned off. We set levels so that the limiter would not be activated. Analog output went directly to the output board to the transmitter.

With the FM analog transmitter, we were shocked at how good FM could sound. Not the equal of the analog output from the player, the FM transmission cut off the very deep bass, and there was just a hair of added background noise, but very very good, better than we ever hear broadcast by any commercial station in our experience. Almost, but not fully the equal of listening to these great sounding CD's and this SACD from the player's output.

The 96 kbps single-stream was then turned on. Listening on the station's digital receiver and my Sony MEX-DV2000, back in my car, we all agreed that it was almost as good as or just as good as the FM analog transmission, with a slightly cleaner background, but somewhat less detailed sound. A hair more seperation and low bass. High end not quite as clean, which surprised us.

We did not have time to turn on the second HD2 stream nor could we try pure digital FM without analog.

So can HD FM radio sound almost like CD quality, yes it can; but then, so can analog FM, and that is sort of the crime. Get rid of the really bad practices that have infected the audio quality of FM and my ears will thank you. In practice, none of the commercial FM stations in my area are sending out a digital FM sound that comes close to great analog FM, never mind CD quality.

As for HD-2. It sounds to my ears much better than it should, but when I am driving around and the HD-2 signal drops out the radio reverts to either the HD-1 alternative broadcast or the analog FM alternative broadcast with different content. This is a shock to my system. Didn't anyone figure this out before they thought HD-2 was going to help save "free radio?"

Richard

I would have to say that this is more likely your receivers fault then anything else, as the loss of an HD2 or HD3 digital signal will typically result in silence rather than a channel switch to the HD1 broadcast on the receivers I have dealt with. I could also imagine how horrid that switching would sound.

My JVC certainly never reverts to the HD1 or analog signal when HD2 drops out, and that would be a ridiculous design if it did. I have not, however, let it sit in silence for 60+ seconds at any time, though; if I lose my HD signal for more than a few seconds, I know it is time to switch to a closer station.

I should note that this only happened a couple of times, likely where the HD1 and HD2 dropped out at the same time.

I drove across NYS yesterday and sampled a number of HD FM stations, and the sound simply does not match the quality of a good CD to my ears, not by a long shot. The music offered on the various HD2 slots is not my taste, most of the time at least. So I will be glad to continue using my good old multi-channel SACD/CD car radio for most of my music enjoyment in the car.

Richard

I don't even mind there being a polka channel; variety is what is supposed to make satellite readio great ... featuring things you can't get on radio. But XM has about 500,000 country channels and a ton of hit stations, while Sirius has a million light rock stations ... all of them sounding the same. Do we really need all those?

I may be exagerating a little on the numbers, but you get the idea.

Certainly it's the content that drives people to listen to anything. Fidelity depends on what you are listening to. I think there is somewhat of a drive sometimes to improve on everything even when it can be OK. For example there's a talk fm station that's in hd near me...I've never heard bad talk unless it's on am and gets static or engine noise from a car.

On the other hand I can't picture classical on am. I probably wouldn't exactly get all the fine details of a orchestra unless I was running on a cd (incase it drops etc)

But the ranges of stations varies and so does the quality but it's been that way for stations for decades anyway. Without nightwave I wouldn't be able to get a few fm stations that are decent...

I have to wonder though going forward how some of the further switch offs will go if the hd2 channels ultimatly get commericals and if things go onto the full rather than hybrid mode.

I have purchased a Viston HD Zoom car radio. For the life of me I can't figure out how or where the volume is. What am I overlooking? I have a low volume but I don't know how to turn it up. Can you help me?

There isn't really a volume control since it's got a line out connection and an fm modulator; it should go through the volume in your car stereo. How do you have it connected to the car?

Richard that is an interesting point to make, and I agree with it, with one condition. It can in an environment where you are stationary, with a solid signal from the FM transmitter with no environmental effects.

I say that doing my own test of an Albany, NY FM classical station which has absolutley one of the best sounding HD-1's I have ever heard. I drive a beat up Jeep with a top of the line stereo system and a JVC KDR-HD1 HD radio in it. While driving, listening to this station, the audio coming from my car's sound system, sounded like I was at a concert hall! And the whole time, I was travelling on the NYS Thruway at 70mph. When I forced the receiver back to analog, it sounded analog. By which , I mean, you could hear "picket fencing" and multipath distortion while driving. Go back to the HD, and it's gone. So I agree that analog FM can sound great, HD blows it away in a vehicle, in motion, no matter how good the processing.

Also, stereo FM chops off everything above 15 kHz. That's not CD quality. Even I can hear the difference with modern music full of bright drum machines.