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I've just received some very interesting information from an Apple engineer about the operation of iTunes / Core Audio. I'm going to do some testing, and post the conclusions soon.
For now, I just want to let you all know this:
If you are using iTunes 7.0 or higher, it is important to set the sample-rate in AudioMIDI BEFORE OPENING ITUNES. If you have iTunes open, close it, then set the sample-rate in AudioMIDI. Apparently iTunes locks to the sample-rate that is set in AudioMIDI when iTunes is launched, and the sample-rate can not be changed until iTunes is closed and re-launched.
I'll let you know as I find out more.
Thanks,
Elias
Great update Elias - keep 'em coming!
Would also be very helpful to have the same questions answered for running iTunes under a windows environment (XP in my case) as I run an OSX rig and an XP rig. I presume AudioMIDI is OSX only - is there an XP equivalent or other setting in XP that needs similar attention?
Thanks again Elias - I know you have a myriad of other things to do besides answering the many questions that Head-fi throws at you!
Hello, I just got my Dac-1 in the mail today, I just want to say it sounds terrific, it completely blackens the background. Much louder/lower bass, the windows rattle with my little duo's now. I switched the jumper on the inside to do coax only, only to my chagrin realizing I was not properly grounded while doing it. I'm curious what if anything would be damaged, is there a simpler cure rather than buying a grounding wristband before moving the jumper (nitrile gloves?). What would it cost to have your team fix a unit that was affected by this? I thought I was doing the right thing with the jumper, who knows maybe it's all buggered now, or maybe things go wrong rarely with this issue. I certainly think it sounds fabulous, but what do I know. Thanks again, even my silly mp3's sound great.
I've just received some very interesting information from an Apple engineer about the operation of iTunes / Core Audio. I'm going to do some testing, and post the conclusions soon.
For now, I just want to let you all know this:
If you are using iTunes 7.0 or higher, it is important to set the sample-rate in AudioMIDI BEFORE OPENING ITUNES. If you have iTunes open, close it, then set the sample-rate in AudioMIDI. Apparently iTunes locks to the sample-rate that is set in AudioMIDI when iTunes is launched, and the sample-rate can not be changed until iTunes is closed and re-launched.
Elias, others;
Ok here is how it works as I just tested this again.
If you set the Fs rate in the Audio pane of the Audio Midi Setup to say 96k. Then you start iTunes and play then CoreAudio is told to upsample from 44.1 to 96k.
If you go into Audio Midi Setup during your iTunes session and reset this to something (like 44.1) else then it will follow. You don't have to leave iTunes to change the sampling rate.
Therefore say if you are playing Red book stuff but then want to play high rez stuff, keep iTunes and Audio Midi Setup up and change the rate according to the needs of the track.
As for quality of the upsampling got me, I am not one for mucking with the data.
Test Setup: G5 Dual ---->USB Analyzer-->DAC--->Test System
I used for the dac both my Crimson and the Benchmark both had the same results.
With the USB Analyzer I can easily tell what the Fs rate is by the amount of data sent per frame @ 1ms.
Thanks
Gordon
__________________
J. Gordon Rankin
Wavelength Audio, ltd.
Hello, I just got my Dac-1 in the mail today, I just want to say it sounds terrific, it completely blackens the background. Much louder/lower bass, the windows rattle with my little duo's now. I switched the jumper on the inside to do coax only, only to my chagrin realizing I was not properly grounded while doing it. I'm curious what if anything would be damaged, is there a simpler cure rather than buying a grounding wristband before moving the jumper (nitrile gloves?). What would it cost to have your team fix a unit that was affected by this?
Your DAC1 probably did not suffer from any ESD damage as long as you didn't touch any IC's. If there was any damage, you would hear it. The only precaution necessary before changing the jumpers is to touch the chassis wall first to discharge any major ESD build up. This will NOT prevent ESD altogether, but it will release the majority of any build up so that there are no large arc's.
If the unit has suffered any ESD damage, we would repair the unit without charge since it is under warranty.
Hi Elias, thanks for all your help, when you say touch ic's, do you mean the interconnects on the back of the unit, or any connecting wires within the unit? For any non-professionals out there, I tried to boost the rca output with the trim pots on the back, but it induces distortion on my stereo immediately. On the flip side, I can turn my stereo up higher instead without adding noise, so I just let the amp give me more volume instead of trying to give it a higher signal. Cheers.
If you set the Fs rate in the Audio pane of the Audio Midi Setup to say 96k. Then you start iTunes and play then CoreAudio is told to upsample from 44.1 to 96k.
If you go into Audio Midi Setup during your iTunes session and reset this to something (like 44.1) else then it will follow. You don't have to leave iTunes to change the sampling rate.
Therefore say if you are playing Red book stuff but then want to play high rez stuff, keep iTunes and Audio Midi Setup up and change the rate according to the needs of the track.
I'm afraid I disagree. According to an Apple engineer and my testing, iTunes locks to the sample-rate of CoreAudio (AudioMIDI) upon launching. After iTunes is launched, you can change the Fs of CoreAudio via AudioMIDI, and the newly set Fs will apply to the output of CoreAudio. However, iTunes itself will still be locked at the initial rate. The audio will be SRC'd by CoreAudio to the newly set rate. That is why it looks like the Fs is changing....CoreAudio's Fs is changing, but iTunes is not.
For example, if CoreAudio Fs is set to 96k in AudioMIDI when iTunes is launched, iTunes will be locked at 96 kHz output. If you play a 44.1 kHz iTunes will SRC it to 96 kHz before sending it to CoreAudio. If you then change AudioMIDI (CoreAudio) to 44.1, CoreAudio will SRC the 96k that it is receiving from iTunes to 44.1. The resulting output will be 44.1 kHz, but it is 96k in-between iTunes and CoreAudio. This is why you see the sample-rate following AudioMIDI...it will!! But iTunes output sample-rate is not changing, and CoreAudio is SRC'ing it to the set rate.
iTunes output Fs will not change until you re-launch iTunes. At that time, it will lock to the Fs currently set in AudioMIDI.
(In case anyone is confused about the difference between AudioMIDI and CoreAudio: CoreAudio is the audio engine in OS X. AudioMIDI is simply the user interface to CoreAudio - that is, the window where you can change the settings of CoreAudio.).
I should say that this is all tested with OSX 10.4.5 (Tiger). Gordon may be getting different results because of Leopard. I have ordered Leopard, and it will be here early next week.
However, the engineer from Apple said this is a decision they made when designing iTunes 7.0 and up, so it shouldn't be affected by the OS.
Originally Posted by Wavelength
As for quality of the upsampling got me, I am not one for mucking with the data.
Ideally, we wouldn't have to change anything to avoid SRC. Unfortunately, OS X is set up in such a fashion that it is a task to avoid SRC. But they seem willing to work with us re: bugs, so maybe there are brighter days ahead...maybe.
Hi Elias, thanks for all your help, when you say touch ic's, do you mean the interconnects on the back of the unit, or any connecting wires within the unit? For any non-professionals out there, I tried to boost the rca output with the trim pots on the back, but it induces distortion on my stereo immediately. On the flip side, I can turn my stereo up higher instead without adding noise, so I just let the amp give me more volume instead of trying to give it a higher signal. Cheers.
IC = integrated circuit. Aka, the 'chips'. The 'chips' in the DAC1 are the only things that are (realisically) damageable from ESD. If you touch chassis before going inside the unit, and avoid touching the 'chips', you should be fine.
For any non-professionals out there, I tried to boost the rca output with the trim pots on the back, but it induces distortion on my stereo immediately. On the flip side, I can turn my stereo up higher instead without adding noise, so I just let the amp give me more volume instead of trying to give it a higher signal. Cheers.
I forgot to say in my last post...
The thing you did with the RCA's is the right thing to do. That is, set the output to the upper limit before distortion. BUT, unless you have proper testing equipment, it is better to error on the too-low side vs. the too-high side.
Linear Mode
