[Pr_007]

Sanjayc, there is also a cable where you can take audio out from the 3.5mm jack on your PMP/mp3 player and the other end would have a USB kind of a PIN where you can connect it to the USB port.

[sanjayc]

Originally Posted by Pr_007

Sanjayc, there is also a cable where you can take audio out from the 3.5mm jack on your PMP/mp3 player and the other end would have a USB kind of a PIN where you can connect it to the USB port.

Could not understand! The usb cable is used by any hu to access the mp3 etc stored on a usb drive and then the files are decoded internally in the HU - how would connecting 3.5 jack, which just carries analog audio signals be connected to the usb jack of the HU? Or, Am I missing something here?

[DerAlte]

Originally Posted by Pr_007

... take audio out from the 3.5mm jack on your PMP/mp3 player and the other end would have a USB kind of a PIN where you can connect it to the USB port.

If one does that, all one would here is a very comforting and relaxing silence (and maybe see an error message on the HU).

USB port contains 4 pins: +5V, D+, D- and GND. D+ and D- are serial digital signal pins. If one connects output from an analog device to the D+ & D- pins, the hardware will not be able figure out any 1's and 0's expected in the serial digital data, and will think that there is no signal coming, and output no data to the mixer in the HU, and hence no music.

Originally Posted by sanjayc

... Or, Am I missing something here?

No, nothing much, just the climax scene. Sorry, couldn't help it!

[mohitd]

@Kiran - thanks for the idea, but sorry I can't afford to spend more money(already have and air filter and exhaust lined up in my list of expenses )
@deralte - I agree with what you said. You cannot connect a 3.5 pin to USB with any interconnects as it will be pointless.

Has anyone faced a similar problem? Is there anything that can be done or is it a lost battle?

[navin]

Originally Posted by DerAlte

USB port contains 4 pins: +5V, D+, D- and GND. D+ and D- are serial digital signal pins. If one connects output from an analog device to the D+ & D- pins, the hardware will not be able figure out any 1's and 0's expected in the serial digital data, and will think that there is no signal coming, and output no data to the mixer in the HU, and hence no music.!

I know the ipods expect some +/-2 2V signals at D+ and D- as well. So if the USB port is putting DC at D+/D- this can damage any non USB device connected to the USB port.

[abhibh]

Originally Posted by mohitd

@Kiran - thanks for the idea, but sorry I can't afford to spend more money(already have and air filter and exhaust lined up in my list of expenses )
@deralte - I agree with what you said. You cannot connect a 3.5 pin to USB with any interconnects as it will be pointless.

Has anyone faced a similar problem? Is there anything that can be done or is it a lost battle?

I am usually not well versed with iPods as i only like their Classic 120/160 GB ones.

Try some other ipod if your friends have any and see if that works.

[DerAlte]

@mohitd, did you use the same connecting cable in your friends car to check your iPod? If not, your cable might be suspect. And, as @abhibh said, try another (if possible older) iPod in your car to check if that works.

[navin]

The Classics (120/160) also expect some DC at pins 2 and 3 of the USB. I think this DC is derived not from the USB per se but within the cable supplied (via a resistor network). I measured the voltages at the end of the ipod cable (30 pin connector) see PDF below

http://www.qables.com/shop/images/pdf/ipodpinout.pdf

same thing via web link so you can save the same in your browser (note exceptions made for iPhone/Touch and new nano).
http://pinouts.ru/CellularPhones-A-N...r_pinout.shtml

nice photos included here
http://www.allpinouts.org/index.php/...nd_iPhone_dock

short explanation of pins
http://nuxx.net/wiki/iPod_Dock_Connector

[joybhowmik]

If you are trying to get lossless output - suggest you stick with OEM CDs and play that on a properly cleaned HU, with good speakers and good wiring.

Be prepared for loss in signal due to
a) interface loss when you port the song to a flash drive, ipod or other player and connect HU to it
b) signal loss when you change the format from native recording format to mp3, flac etc

However, for most people, this loss in quality is acceptable as the environmental noise in a car is higher than in a recording studio - so people hardly notice either form of loss over for example wind noise or tyre noise.

[DerAlte]

Originally Posted by joybhowmik

... a) interface loss when you port the song to a flash drive, ipod or other player and connect HU to it...

Why would that cause ANY loss? Those interfaces are not meant to lose bits and bytes. There would be a corresponding loss in general data, if so, leading to a possibility of 'woman' becoming 'man' in a text document, for example.

[joybhowmik]

Originally Posted by DerAlte

Why would that cause ANY loss? Those interfaces are not meant to lose bits and bytes. There would be a corresponding loss in general data, if so, leading to a possibility of 'woman' becoming 'man' in a text document, for example.

This is because digital signal processors can drop information bits albeit to a lesser extent than analog signal processors. But the loss is known to happen. You don't see this in networked computers (based on your example above) because networking protocols have in-built mechanisms to resend message in case of send/receive failures.
However, in real-time when two DSPs are connected to each other there is a possibility of drops.

[joybhowmik]

@DerAlte
Another explanation as I could not modify my earlier response-but essentially the same thing:
Signal loss/Information loss can happen either inside the synchronously connected DSP or their interface. example a PMP connected to a HU using any interfacing mechanism.
On the other hand, when two DSPs are asynchronously connected using any interfacing mechanism, they may choose to implement mechanisms which guarantee information delivery. An example is networked computers, which rely on the networking protocol to calibrate the information content and exchange meta-data, thereby each computer is then able to request a message resend, in case the meta-data does not match the content received.

[DerAlte]

Originally Posted by joybhowmik

... digital signal processors can drop information bits albeit to a lesser extent than analog signal processors. But the loss is known to happen. ...

Originally Posted by joybhowmik

... Signal loss/Information loss can happen either inside the synchronously connected DSP or their interface. example a PMP connected to a HU using any interfacing mechanism ...

This is a very involved subject where simple assumptions and modeling does not help.

The processors, neither the analog ones nor the digital ones, 'drop information' within the chip real estate. (Massive dose of) EMI interference may cause information or signal to be corrupted, like when old 2-stroke engine autos induce when standing beside you at a traffic signal. But, that is not the chip's fault. I am sure TBHP members who are into chip design will be able to quote real numbers of bit, byte or signal drop within the processors.

USB communication (short cable length, lower frequency than Ethernet), as opposed to networking communication (long cable lengths, much higher frequency), is much less susceptible to interference which is the main cause of drops.

Analog signal transmission to Aux-in, on the other hand, is much more susceptible to interference. Prevention: better shielded cables, even though one cannot obviate interference. Interference shows up more, and that also directly on the signal for longer durations than digital reproduction. Analog is also affected by line capacitance/inductance, which causes information loss (much less 'air' in high frequencies).

Since in digital reproduction, the possibility of frame decompression failure on bit / byte drop is higher than when bytes are decompressed at source (or not compressed at all), streamed uncompressed music (WAV) is always better than even loss-less compression. Here, frame = set of bytes representing a longer duration of music than the much smaller set of bytes representing the smallest duration of music in digital reproduction.

Originally Posted by joybhowmik

... However, in real-time when two DSPs are connected to each other there is a possibility of drops.

Theoretical possibility is always there. However, to know the practical impact on enjoyment of music, one has to relate to the real probability of that happening.

There are ways of calculating this, and data exists from studies in academics. Engineering of electronics deals with this very pragmatically to obviate the factors that contribute to data / signal failure. One wouldn't lose sleep on that, since there are hundreds of engineers who have studied it and created preventive measures.

[joybhowmik]

Originally Posted by DerAlte

This is a very involved subject where simple assumptions and modeling does not help.

Quite right. I tried to simplify this - but basically the more the complexity of the end-to-end system, the more chances of something going wrong somewhere. Most people in most circumstances can live with these inaccuracies - however, in a true sense it would not be technically lossless - which is what I was originally referring to.
At risk of , would affirm that signal corruption within digital circuitry is a given. It always happens - and I am yet to see a circuit which can protect against it 100% of the time. Most manufacturers avoid liability by publishing the operating ranges - which works for most of the situations most of the time.

Also as you have rightly pointed out , wires used to connect PMP to HU could pick up interference, and at that point it is really up to the logic embedded/written in the PLC of the HU to ignore the offending input. Better shielding is an answer, however, in a country such as ours - everyone may not have access to high quality connectors -and these are expensive also.

[mohitd]

Thank You so much guys. My Ipod is working just fine after I updated the firmware My head unit reads ALAC off the ipod straight. Thank You guys.