soundcheck;540814 Wrote: > I am wondering if it is a good idea to take the headphone output as > reference. > As far as I have seen (within Alsa) the headphone out seems to be fired > by a Wolfson WM 8974. > The AKM DAC for the analog out has much better specs. Still I'd guess > that the SPDIF performs best, since also the AKM can't be called a > high-end performer if you look at the datasheet. > > I looked up the specs of both chips. The Wolfson chip specs are not > what I'd call impressive. It seems that they havn't put much focus on > the headphone output. > > The Wolfson is btw running 16 bit and 48khz max. (It seems that they > are running it with a 2nd jive_alsa process - AKM and SPDIF though goes > 24bit and are fired in parallel by Alsa) > > No idea if they add dither to the 16bit signal of the Wolfson after > volume control. Usually this should be done. This would change the > results even further. > > So. If measurements should be done, than SPDIF is IMO the first > choice. > > Cheers
Thats not correct, the Wolfson DAC is only used for the internal speaker used for the bleeps and blurps etc. The AKM chip goes to both the headphone amp and the analog outs. The analog outs have a resistor and one cap in the path between the DAC and RCA Jacks. The headphone out has a cap, resistor, the headphone amp and another cap. There is no way to have different volume for the headphone RCA outs, they are the same. The headphone out can also be shared by the IR blaster circuit. There is an enable signal to each (headphone amp and IR blaster). I haven't looked carefully at that circuit to see exactly what it does. The S/PDIF input comes directly out of the main processor as does the two I2S streams that feed the DACs. All three of these are reclocked after the processor. There are two clock muxes, one for the Wolfson and one for the main audio which clocks both the S/PDIF and the AKM DAC. I think the headphone amp is running off a separate regulator from the rest of the audio circuit. I think there is a DC-DC converter to get a higher voltage for the headphone amp. John S. -- JohnSwenson ------------------------------------------------------------------------ JohnSwenson's Profile: http://forums.slimdevices.com/member.php?userid=5974 View this thread: http://forums.slimdevices.com/showthread.php?t=77908 _______________________________________________ Touch mailing list [email protected] http://lists.slimdevices.com/mailman/listinfo/touch
