Mike Walker said:
RBruceCarter, with all due respect, maybe some practical experience would be useful before opining on a subject.
The tuner in my Media Center PC (HP m470n) is actually among the best fm tuners I've owned.
I've got the same type of board in my HP Media Center PC. Hooked up to a good yagi antenna, it doesn't come anywhere close to the performance of even modest tuners from the 70's.
To begin with - it needs to have the narrow ceramic filter modification done. Probably not easy to do - since it may be surface mount inside of a metal RF shield. Every RF engineer knows those surface mount Murata ceramic filters are not nearly as good as the old through hole variety. Hopfully there is room to put decent filters on the board on the surface mount pads.
Based on the levels of sideband interference, I suspect there are only two filters on the board. Not insurmountable, but it will make rejection of adjacent stations more difficult. One of my benchmark tests is 102.7 from Abilene, about 180 miles away. Easy for my vintage Heath AJ-15, which is relatively modest by classic tuner standards.
After that, I ramp up the difficulty looking for 250 and 300 mile type of reception. That requires a very good tuner, with a very low noise front end. Only a dozen or so classic tuners from the 70's can manage it un-modified in stock configuration. I doubt that - given the cost of your average PC tuner board - they can afford the $100 low noise FET's required in the front end.
I have to laugh a bit when people start bragging about Accuran, Bose, Boston Acoustics, etc. The very nature of such products is rampant with audio compromise. In order to fully evaluate their tuner's circuitry and its performance, I would need to bypass their internal amplifier and speakers, and hook up to a really good discrete amplifier and studio quality speakers. Only then could I get an idea of their sonic improvement in and out of HD mode. Hopefully, I could gain access to a good RF generator and harmonic distortion analyzer and evaluate - end to end - under laboratory conditions - these claims that HD sounds better. I am very suspicious of digital anything, because the sampling nature of digital music implies a given resolution, and information is lost - somewhat akin to .jpg encoding for pictures. "CD qualitiy" makes me laugh, because the 16 bit resolution absolutely limits you to a 96 dB signal to noise ratio at best, minus the performance of the interface circuitry. Contrast that to a 120 to 130 dB signal to noise ratio possible in a quality analog signal chain from 10 1/2 reels or vinyl. The difference is striking when you have good equipment. Given that HD requires a compression algorithm, and they split it up to get HD-2 channels, thus sampling at a lower bit rate - I am really suspicious of the result.
I will grant you that mono FM is limited to about 74 dB signal to noise, and stereo to about 52 dB signal to noise. Obviously, increasing that to CD quality would be an improvement. But I doubt the cheap little speakers put into these trendy table radios could tell that type of difference. Let alone the cheap transistors and IC's used in their audio chain. If somebody is selling a trendy radio for $200, most of that price is for the prestige of the name, I doubt there is over $20 of actual electronic parts in there. It certainly rules out the expensive FET's required for real fringe reception, it probably rules out the selection of IF filters for really flat IF passband response that would translate into lower harmonic distortion. And the wide IF response required to pass out of channel sidebands required for HD reception would completely wreck the selectivity, and probably the sensitivity as well, of the radio.
HD may be great for people living within 10 miles of towers in a densely packed metro area. But for the rest of the country, it is a white elephant ready to become extinct. The HD folks marginalize and belittle the only people who would know how to receive it at any distance: FM DX'ers. Without input from the DX community, the potential audience for HD will be limited to areas near the towers. Prosperous suburban people will own HD radios that never make it out of analog mode.
