Maddog-99

A question for those more audio / technically inclined.

My problem is specific, but the input Im looking for is broad.

Problem:
Ive recently done the CIC + Combox upgrade with Bimmerfest.
I have full ipod integration with 6NR & FL, and this an important feature for me (more for audio & podcasts, but video as well).

BMWs OEM solution is set up so audio coming from this source is an analog signal.
This is required to keep the audio & video in sync when playing video off the ipod/phone/touch.

Bimmerfest wisely precoded this source to be digital to provide the best fidelity on audio.
But the Video is now a second ahead of the audio when playing from my ipod.

Bimmerfest has been helpful in letting me choose which solution I want & will change it accordingly.

Question:
How noticeable to my ear & to my audio system is the analog feed for ipod audio vs. the digital feed?
On homestereos I know I need digital to get surround sound & generally highest quality sound.

In this case, from what Ive read, it comes down to which DAC (digital to analog converter) I want processing the signal as ultimately it ends up an analog signal.
If the port is digital: then the cars DAC does the work
If the port is analog: Im relying on the ipod/phone to do the work

Presumably the Car does a better job & sounds better?

Any / All input is welcome.
Correct me if Im wrong above.

Key question for me is, can I tell the difference in quality?
Ill be doing audio 90% of the time & video 10% of the time, so I don?t want to screw up audio for the sake of video.
Is there a way to dry run this so I can compare?

tpaxadpom

I keep hearing the quality comes down to the choice of DAC used. This is far away from the truth. It is about the DAC, analog stage, PSU quality and many other things. Most DACs today are 24 bit, but the best analog stage is ~20bit (120dB signal to noise ratio).
Ipod doc has analog audio and usb interface. Typically in home audio you use SPDIF, AES/EBU, Toslink, AT&T Glass, HDMI or various versions of I2S via CAT5 or HDMI...
BMW stereo has ADC (analog to digital converter) connected to the Aux. The input stage is somewhat limited in terms of maximum voltage swing allowed. My wife's ipod or her phone connected via aux input with volume set to max will cause clipping (audible distortion). Dropping the volume a few notches down fixes the problem. This is the first time I came across a car stereo where I could make it clip via analog in using the ipod/phone headphones out.
Analog line output(30pin connector): Ipod built in DAC - BMW ADC converter - BMW DAC converter
Analog headphones output: Ipod with built in DAC - IPod headphones amp - BMW ADC converter - BMW DAC conver
USB output: Ipod usb out - USB-optical converter(what ever the standard it is)- BMW DAC converter

Every conversion has associated latency (amount of time it takes the signal to get through). In your case the USB-optical converter has higher latency than BMW ADC converter circuitry. You can fix the problem if you run all your videos on pc software and delay the audio soundtrack to fix the lip sinc problem (positive so it plays ahead of the video). Free app like avidemux can do this easily. You can test drive it until you find the setting that fix your lip sync problem. This may be your solution if you only watch ipod videos in the car only as otherwise you will have a lip sync problem with other devices.

Which one would be better I cannot tell you. In theory if you minimize ADC/DAC conversion it should be better (digital conversion).
I don't know anything about the ipod adapter in the BMW. For home audio Wadia was one of the first to introduce digital out adapter for ipod http://www.stereophile.com/news/010408wadia/

Maddog-99

Thanks Pom,

Very informative, I appreciate the detail.

What Im trying to distill is if I will be able to tell a discrenable difference.
Im guessing not as the stock OEM BMW set up has it as an analog output.

Im trying to trouble shoot this.
ie: is BT audio less fidelity than an analog source? I believe so. If thats true & Im good w/ BT quality audio (A2DP) than Im going to be good w/ Analog.

Also Im trying to rig an analog input so I can test run it & compare to the digital.

Anyone has input, let me know...

tpaxadpom

Like I mentioned before, I know nothing about the CIC package. Perhaps your initial question was about A2DP (digital) vs analog audio input and usb ipod compatible adapter doesn?t even exist. As far as A2DP vs analog in here is what I think about it.
Bluetooth supports multiple audio codecs (compression algorithms) for A2DP stream. APT-X is one of them and it does have lossless mode of operation http://en.wikipedia.org/wiki/Apt-X. In general only a few devices on the market support that mode. Iphones do (latest gens I believe), I have no idea if BMW Bluetooth module does. If it doesn?t then you will get additional compression (think cd quality vs mp3). Generally I would prefer analog connection (as long as you don?t overdrive ADC input stage) as APT-x lossless is not widely accepted. I have been working with wireless audio for a while. It is hard to get bit perfect wireless audio when low latency is a primary concern (lip sync problem in home theater application). If BMW Bluetooth supports lossless and your source offers that it could be better than analog

Maddog-99

Thanks Pom,

Great discussion, appreciate it. Will be fun if we can get this forum to come up when people are google searching audiophile questions!

So Im going to dumb down what youve said & add a few things. Correct me if Im wrong.

Lossless: Im mostly a 192-256kbps MP3 guy. If that audios coming through clean & well Im good. Beyond that Ill go to a CD for playback for really killer albums.

For my use case Im using a iPhone 4. Ill be turning that into a iTouch that will be dedicated to use in my ride.

From What Ive read, my understanding of audio fidelity relating to connections is:
(This is generalized, but basically acurate)

Digital source output
Analog source output
Bluetooth Audio
Headset Jack output
FM Transmission (ie: wireless transmission to open station)

That stand up to what you know?

Back to my original point: If I enjoy the quality of BT audio in my car, then an analog source for my iphone will be better/fine quality.

tpaxadpom

For the car audio that utilizes digital signal processing (DSP) (analog to digital conversion is required) I would rate them in this order:
Digital source output
Bluetooth Lossless
Analog source output
Headset Jack output
Bluetooth Lossy
FM Transmission (ie: wireless transmission to open station)

I don't like to generalize as there are too many variables.

Burn the mp3 CD with the same tracks as on your phone and compare the sound to A2DP Bluetooth. If the difference is significant to you, you may want to investigate the analog input option. CD mp3 in your case should be the reference. Analog input would be closer to CD mp3 sound if BMW bluetooth doesn't support apt-x lossless. The additional compression should be audible even with low bit rate mp3s (128kb/s).