I finally found at least a partial fix for the audio quality out of the headphone jack on my early 2008 15" MBP. I have a pair of Sennheiser CX-300's which are low impedance compared to, say, standard ipod headphones (and they sound infinitely better). Basically that means if I want to listen to some quiet music, I have to set the volume extremely low. I usually use option+shift+volume up/down to set the volume anywhere from 1/3 of a bar (the minimum) to 1 bar. Even 1/3 of a bar is not really low enough sometimes.
There are two problems at very low volumes. One is that I can hear a constant hiss in the background. Second is if the music gets quiet, the sound output can't get any quieter, and it distorts and sounds like garbage. Music that is supposed to fade out at the end, for example, just distorts and doesn't get much quieter. Taking it to the extreme, I can set the volume slider in iTunes very low while the hardware volume is set to 1/3 of a bar, then everything sounds distorted. I started listening to music exclusively on my desktop PC, which somehow manages to put out really good sounding sound from the integrated sound card.
I haven't found a software fix for the hiss (an attenuator AKA volume knob would fix this, such as http://www.amazon.com/Shure-EA650-Control-Isolating-Earphones/dp/B000GTBDBA), and I know that's just electrical noise from the MBP, but I was able to fix the distortion. In Audio MIDI Setup, I simply changed the output from 16 bit to 24 bit and the problem disappeared. I also switched from 44100KHz to 96000KHz, but I couldn't hear any obvious difference with that change (and since all my music comes from 44100 CDs, I probably won't ever hear a difference. Maybe I can find music from a SACD or DVD-audio disc).
I'll probably keep listening on my PC because of the hiss issue, but at least my MBP is a lot better now.
There are two problems at very low volumes. One is that I can hear a constant hiss in the background. Second is if the music gets quiet, the sound output can't get any quieter, and it distorts and sounds like garbage. Music that is supposed to fade out at the end, for example, just distorts and doesn't get much quieter. Taking it to the extreme, I can set the volume slider in iTunes very low while the hardware volume is set to 1/3 of a bar, then everything sounds distorted. I started listening to music exclusively on my desktop PC, which somehow manages to put out really good sounding sound from the integrated sound card.
I haven't found a software fix for the hiss (an attenuator AKA volume knob would fix this, such as http://www.amazon.com/Shure-EA650-Control-Isolating-Earphones/dp/B000GTBDBA), and I know that's just electrical noise from the MBP, but I was able to fix the distortion. In Audio MIDI Setup, I simply changed the output from 16 bit to 24 bit and the problem disappeared. I also switched from 44100KHz to 96000KHz, but I couldn't hear any obvious difference with that change (and since all my music comes from 44100 CDs, I probably won't ever hear a difference. Maybe I can find music from a SACD or DVD-audio disc).
I'll probably keep listening on my PC because of the hiss issue, but at least my MBP is a lot better now.
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