Rockbox for iPod Video Fully Finished??
Mar 3, 2006 at 2:51 PM Post #31 of 73

K2Grey

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The thing is, the volume control is probably digital in nature. So the internal amp is bypassed whether you actively change the volume or not. But most people who use the line-out use an amp with a volume control with it; thus there's no need for a 2nd volume control.
 
Mar 3, 2006 at 4:12 PM Post #32 of 73

linuxstb

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Quote:

Originally Posted by greenleaves
The main reason for using the line-out is so that we can have clean signals directly coming from the DAC, bypassing the iPod internal amp, and all fine ampification is done by the external amp. Bypassing the internal amp for external control is the crux of the concern for all audiophiles in their setup.

I suggest that Rockbox should fix the line-out at 0db by default. It would be a nice option in the Rockbox setting should the user decide to use the volume control for the line-out.



The point is that there will be ABSOLUTELY NO DIFFERENCE to the audio path between Rockbox fixing the line-out at 0dB and the user setting the line-out to 0dB using the volume control. The values written to the registers in the DAC will be the same.

If there was a way to bypass the internal amps, Rockbox could simply do that whenever 0dB was selected by the user - but there doesn't appear to be a way to do that.
 
Mar 3, 2006 at 4:17 PM Post #33 of 73

Yotam

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linuxtb,

Are you one of the fevelopers of the 3g version? if yes, how is it going?

anyway, thanks for your great work!
 
Mar 3, 2006 at 6:17 PM Post #35 of 73

greenleaves

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Quote:

Originally Posted by linuxstb
The point is that there will be ABSOLUTELY NO DIFFERENCE to the audio path between Rockbox fixing the line-out at 0dB and the user setting the line-out to 0dB using the volume control. The values written to the registers in the DAC will be the same.

If there was a way to bypass the internal amps, Rockbox could simply do that whenever 0dB was selected by the user - but there doesn't appear to be a way to do that.



Upon reading the signal path diagrams (WM8983) on page 1 and 12, I can confirm that the headphone out and the line-out in fact shares the same audio path. This means that there will be absolutely no difference in terms of sound quality for both. Thanks for pointing out this fact to us.

Furthermore using the iPod firmware for the line-out, I also find that the EQ is still functioning even though the volume control is bypassed. This means that the line-out is just another headphone out in 5G. The only difference is that the iPod firmware disables the volume control in the line-out when using it. Honestly, I was a little disappointed of this finding.
frown.gif


I would like also to point out the fact that the DAC used in 5G is WM87588G not WM8983 we are referring to according to the link below but I could not find the WM87588G datasheet on the Wolfson web site. I hope the difference between the two is minimal. Here is the link referred on the ipodlinux web site.

http://arstechnica.com/reviews/hardw...deo-ipod.ars/6

I still wish to see Rockbox would set the line-out to 0db whenever possible by default. I believe it is a good feature to save users trouble from having two volume sets to control.

Many thanks.
 
Mar 3, 2006 at 6:23 PM Post #36 of 73

greenleaves

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Quote:

Originally Posted by skaggers
Greenleaves,

You are getting confused between the signal running through the headphone amplifier and the signal being volume attenuated in the DAC, the headphone amplifier circutry is bypassed when using the line out. Variable line outs can still be true lineouts. Software cannot change the hardwired signal paths.



Unfortunately the headphone amp circuity is not bypassed when using the line-out. This is something that I would have hoped for in the beginning but it is not the case. Please read my post above.
 
Mar 3, 2006 at 8:38 PM Post #38 of 73

Jahn

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so instead of using the lineout from the dock via a pocketdock or sik din or turbodock, we can achieve the same SQ if we use the headphone out and turn the volume up to 0db then send that signal from the headphone out to the portable amp?


if this is really the case, let me know, and then i'll just use the dock for apple's radio dock and rely on the headphone out as the analog out to my amp.
 
Mar 3, 2006 at 8:51 PM Post #39 of 73

muckshot

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Quote:

Originally Posted by greenleaves
...the headphone amp circuity is not bypassed when using the line-out


So if this says what I think it says, the placebo effect is alive & well here at Head-fi :p
 
Mar 3, 2006 at 10:50 PM Post #40 of 73

K2Grey

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I think Greenleaves is jumping to conclusions. The headphone out and line out of the DAC are the same. That does not mean the headphone out and line out of the iPod are the same. Apple may very well, and probably does, put things between the DAC's headphone out and the iPod headphone out, which are not between the DAC's line out and the iPod proprietary connector which leads to the line out of PocketDock for example.

Edit: Of course, I do not own a line out adapter right now so if someone proves that the amount of stuff between the headphone out and line out of the iPod (not the DAC) is similar, then I will be happy to hear that
smily_headphones1.gif
 
Mar 3, 2006 at 11:22 PM Post #41 of 73

greenleaves

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Quote:

Originally Posted by K2Grey
I think Greenleaves is jumping to conclusions. The headphone out and line out of the DAC are the same. That does not mean the headphone out and line out of the iPod are the same. Apple may very well, and probably does, put things between the DAC's headphone out and the iPod headphone out, which are not between the DAC's line out and the iPod proprietary connector which leads to the line out of PocketDock for example.

Edit: Of course, I do not own a line out adapter right now so if someone proves that the amount of stuff between the headphone out and line out of the iPod (not the DAC) is similar, then I will be happy to hear that
smily_headphones1.gif



I came to the conclusion based on the fact that the Wolfson WM8983 Codec handles both the DAC and the amp stage within the chip. Please read the datasheet. I see no reasons why Apple would have put another amp on the final output stage. I am no expert in Wolfson Codec, and I could be wrong!

On the Wolfson web site, I quote "The device integrates preamps for stereo differential mics, and includes drivers for speaker, headphone and differential or stereo line output. External component requirements are reduced as no separate microphone or headphone amplifiers are required." Here is the spec:

http://www.wolfson.co.uk/products/di...codecs/WM8983/

I'm sure there are something in between the Codec and the outputs. Most probably are volume/gain control stuffs according to the datasheet. But will they affect the SQ on both outputs?

It would be nice if someone could make a sonic comparison between the headphone out and the line-out using the iPod firmware, and let us what you think.
 
Mar 4, 2006 at 12:22 AM Post #42 of 73
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Quote:

Originally Posted by greenleaves
I came to the conclusion based on the fact that the Wolfson WM8983 Codec handles both the DAC and the amp stage within the chip. Please read the datasheet. I see no reasons why Apple would have put another amp on the final output stage. I am no expert in Wolfson Codec, and I could be wrong!

On the Wolfson web site, I quote "The device integrates preamps for stereo differential mics, and includes drivers for speaker, headphone and differential or stereo line output. External component requirements are reduced as no separate microphone or headphone amplifiers are required." Here is the spec:

http://www.wolfson.co.uk/products/di...codecs/WM8983/

I'm sure there are something in between the Codec and the outputs. Most probably are volume/gain control stuffs according to the datasheet. But will they affect the SQ on both outputs?

It would be nice if someone could make a sonic comparison between the headphone out and the line-out using the iPod firmware, and let us what you think.




Interesting. This confirms my experience with the 5G iPod lineout when I tried to justify carrying around a portable amp a couple months ago. At first when using a Ram Din and external amp, it seems the lineout has more "kick" than the headphone out, but I think most people unconsciously tend to listen at slightly higher volumes when using an amp, and I am no exception. After I tried to volume match as best I could, I really couldn't tell any difference between the HP out and the lineout, and thus now I leave the amps at home. This news that they are one in the same, corroborates my own anecdotal evidence.
 
Mar 4, 2006 at 12:59 AM Post #43 of 73

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I just plugged may KSC75's directly into the TurbodockII on my 5G. While there is sound it is definitely NOT as loud as the headphone output is when set to max.
 
Mar 4, 2006 at 1:40 AM Post #44 of 73

K2Grey

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While the DAC may indeed be handling the task of amplification, it's still not necessarily the case that Apple did not put caps or whatever in the signal path and so on. I really doubt it's a direct DAC - out connection. It'd probably be nice if someone could open up their iPod and post the components for both headphone and line out signal paths.

Dpippel: From reading the thread it seems like the line out is at 0db while the headphone out can go up to +6db. But methinks that if you push the volume control into gain you'll get clipping and the like.
 
Mar 4, 2006 at 1:51 AM Post #45 of 73

swmtnbiker

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Quote:

Originally Posted by K2Grey
Dpippel: From reading the thread it seems like the line out is at 0db while the headphone out can go up to +6db. But methinks that if you push the volume control into gain you'll get clipping and the like.


I don't have an SPL meter, but I can tell you from experience that the difference in volume between the headphone output at max and the line out output is a lot more than 6dB. You're right that max volume on the headphone output sounds pretty crappy.
 

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