Currently, I used line-level signal from IPOD dock as the input to headunit AUX, then IPOD lost the function of volume control. If I direct PC audio to AUX, how about the volume control? Both of them can control volume? or only heardunit can control?
I found the IPOD line-level output was much better than headphone output(Why?). Does PC sound card also have such line-level output?
So why IPOD lost the volume function when using it's line level output? Is it that IPOD can not improve line level signal strength? now a common question is how volume control works. It is control via the signal voltage or something else? seems my HU has a 5V output and no volume control on AMP, how HU control the volume?
Actually, I want to use PC as the master volume. but the steering wheel volume button works for HU. Is there a simple way?
AMP <--- HU <--- PC
Amps never control volume, their job is to amplify the output of a preamp. Your 5v output on your HU preamp is going to be better (wider and cleaner dynamic range) than your PC unless you have a high end sound card, so it'd be better suited for volume control. But if you don't care about that (which is weird, why would you buy a nice HU like that if you're just going to use it as a passthrough), having the volume control on the touchscreen, where you adjust everything else, is convenient. But you might as well just route your audio directly from your PC to your amps.
Just for your own information, line-level outputs are constant on most units like an IPOD. I've had a few mp3 players and all have had constant voltage output on the line out. They are intended to be used with a radio head unit that can amplify the signal and control the volume. Or at home with a receiver.
Thanks guys. Here is my understanding
1) IPOD has a constant line-level output, that is the reason it lost the volume control.
2) PC sound card also support line-level output. Furthermore, it's output can be adjusted via volume control. (what is adjusted? voltage or current?)
I need keep HU which works with PDC to produce voice alarm when parking. The alarm voice has a constant volume in any audio mode (radio, cd, aux). I have two solutions:
a) AMP <---- HU <----- PC
b) AMP <---- HU
Solution a) should works well, but AUX is 2 channel stereo audio. For solution b), 4 or 5 channel can be supported. However, does AMP can mix two audio source? since I need the PDC alarm.
I would go with solution A. You say 4 or 5 channel is not supported but if you're only playing music, it's 2 channel recordings anyway.
the amplifier does have a volume control (the gain control), but that's only a one time adjustment to match the amp input voltage to the headunit's pre-amp output voltage. the amp doesn't control the audio signal, it simply amplifies whatever is being fed into it. when you raise/lower the headunit volume, the pre-amp output signal that feeds the amp is also raised/lowered.
to use the PC as the "master volume control" you'll have to leave the headunit volume at 100% (or close to it). this often results in a constant hiss or hum at low volumes. if you're going to keep your headunit then you should use that as the master volume control.
but if you insist on using the PC as your volume control despite the sound quality implications of doing so, then you can use your steering wheel buttons to control the PC volume. there are several threads and guides on this forum that show how to do this and what you will need to buy.
is there a separate input on the headunit (or stock amp) for this "PDC voice alarm"?
PDC is 'Parking Distance Control'. It uses ultrasonic sensors to measure the distance to object and sends distance data to CAN-BUS. When recevied the packets from bus, headunit will emits acoustic PDC warnings via mid-range loudspeakers(x4). The interesting thing is that the PDC warning voice is constant, even set HU volume to 0. Can't understand how headunit do this. Mix audio function? I am sure that AMP only take HU's signal as input, AMP can not handle CAN-BUS packets.
I need relocate the HU and put a touch screen. Seems that control volume at HU is better than at PC. Here is planned solution:
Set PC volume to 100%. When adjust volume on touchscreen, PC will send packets to CAN-BUS. The way is just like steering wheel button. As the steering wheel button, it works as usual.