Dolby Noise Reduction on GM UB1?

uxwbill · May 25, 2013

I recently changed out the radio in my 2007 Chevrolet Silverado Classic, from a UB0 CD player only model to a UB1 tape/CD combination model. The UB1 radio came from a 2005 Silverado and was reprogrammed to work with UQ3 speakers.

The sound from normal bias cassettes was OK...not perfect, but good enough. Upon discovering that the UB1 can also detect and play chrome/metal tapes, I decided to try it. These tapes, recorded on a known working Technics RS-M218 cassette deck, sounded awful on the UB1. In particular, the treble portion of the sound was highly uneven. Quiet passages would have muffled treble, while louder passages would open up the high frequency response. The result was an uncomfortable "pumping" effect in the treble portion of the audio. I also noticed this happening with an MP3 player built into a cassette shell.

I wondered if some part of the cassette player were broken, or if the playback heads were dirty/magnetized. Perhaps the radio needed repair.

Before jumping to any conclusions, I tried recording to a metal (type IV) tape with Dolby B noise reduction turned on. This made a HUGE difference in the audio quality when playing the tape back on the UB1. It went from sounding awful to excellent. (I know that using Dolby B NR boosts the high audio frequencies on the tape, but I think that if the radio were broken, I'd still hear the "pumping" effect. Whether my ears are still good enough to perceive it with boosted high frequencies I don't know.)

Neither the 2005 Silverado or 2007 Silverado Classic owner's manuals say anything about Dolby B noise reduction capability. Since I've had these radios apart in the past, I looked up the datasheet for the audio processor. This claims that the IC itself does support Dolby B noise reduction for cassette tapes, but I figured it was unused since there is no apparent way to turn it on or off from the front panel controls.

Does the UB1 really support Dolby B noise reduction? Is there any way to turn it off for cassettes that don't use it and "cassette shell" adapters?

Carder09 · May 25, 2013

Talk about stone age equipment lol. What about an a track or phonograph install as well?

DaveH71 · May 25, 2013

Think it might be time to upgrade bud.

&CDFiXER% · May 25, 2013

On the tapes from the "known working" Technics, how do they sound OK in other equipment? Perhaps the heads or transport itself is out of alignment on the Technics unit and they record/play fine on the Technics but on other equipment the track misalignment from the source becomes an issue?

uxwbill · May 26, 2013

On the tapes from the "known working" Technics, how do they sound OK in other equipment? Perhaps the heads or transport itself is out of alignment on the Technics unit and they record/play fine on the Technics but on other equipment the track misalignment from the source becomes an issue?

Yes, tapes from the Technics deck sound fine in other equipment. I gave it a very thorough servicing about two years ago and the alignment met the factory specification at that time.

uxwbill · May 26, 2013

Talk about stone age equipment lol. What about an a track or phonograph install as well?

Think it might be time to upgrade bud.

Seriously? That's not exactly an incisive or helpful answer to my question.

I have nothing against digital music formats and players. I have an iPod and do the whole iTunes/AmazonMP3 thing. I'm quite well aware that cassette tapes are old school. So what? I like them and they work just fine for what I'm doing!

If you can answer my question, please do. I'd greatly appreciate the help. If you would rather make smarty-pants comments about how I'm listening to my music, please don't feel so obliged.

uxwbill · May 29, 2013

Anyone?

Perhaps the player is just broken somehow. It's had a few sudden reversing fits over the past week. Today when it reversed at the end of a tape side, it started playing at warp speed.

uxwbill · October 23, 2013

After some time spent listening to tapes and making new ones to play in the truck, I've come to the conclusion that Dolby B noise reduction is present and seems to be forced on at all times.

I don't mind using the noise reduction when it comes to actual tapes, but it's severely annoying when a cassette shell adapter is used to play another source into the radio. It makes no difference if the special "cassette adapter" mode mentioned in the manual is used or not.

I guess it's time to look into adding some sort of line level input via the connectors at the back of the set...