iPod nirvana or hookum?

[MatthewB]

So as most of you know I bought a new car and the first thing I did was add eight Alpine speakers and a outboard kicker amp to power the speakers. So after doing some reading I find that I can do better than my iPod nano (fifth generation) with a iPod classic 5 (not the beloved 5.5) but close enough as it has the Wolfson DAC and not the Cirrus chip which is what all iPods (including my nano) have.

Now for those that don't know all iPods built in the past couple years are basically flash drives while the first five generations of the classic iPod are portable hard drives with the Wolfson chips. So after doing some testing using a couple test songs (Rufus Wainwright's Oh what a World, Queensryche Silent Lucidity, and Tina Turner's Private Dancer) I did find a few changes in the tonal quality when comparing between the iPod Classic 5 and my iPod Nano. I found the classic had a smoother sound while the Nano seemed brighter and more crisp to the audio and I also found the bass notes seemed tighter and louder with the Nano. While the classic seemed warmer and not as brash as the Nano and more of what I would expect from my main home theater when listening to music.

Both were connected to the cars built in usb connector and I would play one song then make mental notes of what I just heard and then switch players and play the same song. As we are dealing with a digital signal (either 256kbps AAC or 320 Kbps MP3) I realize it is a lossy compression (for the car I figure it would be good enough as most car decks can't play lossless audio and with road noise I wouldn't notice).

So my point being when dealing with portable music players being connected via usb shouldn't that bypass the built in DAC and my cars head unit should be doing the conversion correct? If that is the case why the difference in audio quality between the two iPods.

 

[Flint]

Yes, you are bypassing the DACs if you are only connecting via USB.

So, if the sound is truly different and the source files are truly identical (make sure the files are the same as many audio programs convert the music to the most appropriate format for the device and could see the Nano as being different in file needs than the Classic)... if the sound is truly different (as in, the levels were identical and the files were identical and the sound was clearly obviously different), then you could assume the players MIGHT (might is important here) be converting the files to a different streaming format to send over the USB connection. This is possibly a very possible possibility.

Another option, and this is just reaching, is that (assuming everything truly is identical in every single way - levels to within 0.5dB and files in the exact same format), is that you really didn't hear any difference.

But here's the bigger issue, for me at least... Why care? This is care audio, and I would argue that as your are making your way through traffic during rush hour, any slight or even moderate change in sound timber won't matter as long as you can hear your favorite music without any annoying artifacts, like high distortion or audible compression artifacts.

 

[Haywood]

Franklin is probably correct about the transcoding. Most car stereos do not play AAC natively, so it is entirely possible that the iPad is transcoding to MP3 or something on the fly. Unlike the difference between lossless and high bit-rate lossy, the difference between direct playback of a lossy file and a lossy-to-lossy transcode is clearly audible in an A-B comparison. I would argue that the impact in a car audio application is somewhat minimal, but there is no doubt it is audible. This is why I am abandoning AAC in favor of FLAC wherever possible. I can always transcode down to any lossy format with no audible degradation (so long as the bit-rate is high enough).

 

[CMonster]

Depending on iTunes settings, it's also possible the songs are being transformed when copied to the device. I rip everything in lossless AAC but for devices with less memory like my wife's Nano, I have it set to copy songs over at a lower bit rate.

 

[MatthewB]

Interesting guys. Yes I am noticing a difference in sound quality between the nano and classic via usb connection. With the nano you can clearly hear cleaner deeper bass with the nano. It's the brashness or better word "brightness" of the nano that I'm not a fan of as I like the smoother tone of the classic.

Something is going on. I've downloaded the same songs direct from my Apple account to both devices so I know the files are the same but with bypassing the built in DAC it seems odd that there is an audible difference.

Agree Flint when driving I shouldn't care but it's just something I noticed.

 

[MatthewB]

Okay so for the past hour I've been researching which DAC is actually being used. From what I've read Apple has only licensed a few aftermarket head units and a couple outboard DAC's that can actually bypass the iPods internal DAC. From what I read even when using a usb connection Apple is doing something in the digital realm to let the internal DAC in the iPods do the conversion unless a company has paid a license fee to Apple to let that companies DAC to do the conversion.

Hence why my head is spinning. If using the usb connection is strictly digital then logic says it's still digital at the connection port and obviously the cars head unit must be doing the DAC but then how can Apple be saying that unless the head unit company is paying a licensing fee then the iPod will control the DAC in the built in iPod.

Apple claims only a handful of aftermarket head units have paid the license fee and one company call widia has an external DAC that has also paid the license fee.

How in blue blazes can a digital signal be controlled by a DAC after its left the iPod and sent digitally thru the usb cable. Makes no sense. This would mean the iPod song is converted from digital to analog in the iPod then converted back to digital to be sent via usb then when the head unit picks up the data file it then converts the digital signal again to analog (again only if paid a licensing fee to Apple) to play the song. This makes no sense. So either Apple is lying and companies are paying a useless license fee that is not needed or Apple really is controlling the DAC in the iPod and manipulating the digital signal somehow. I do know that my OEM Nissan head unit does play Apple protected AAC files but I'm pretty sure they didn't pay a license fee so my head is spinning.

 

[Flint]

You are way over thinking this.

With modern portable audio electronics, the logical DAC is just one small component of the audio chip which also handles DRM, clock, jitter filtering, buffering, stream conditioning, and often the analog stage. Sometime the entire file handling process is managed by the same chip containing the DAC. So, completely bypassing the DAC in every single way isn't always possible with common consumer portable devices. This is also why the high end audio llayers are typically larger and kuch more expensive as they use discreet silicon components which need larger circuit cards and with more components increase cost.

So... If you really want to.complete bypass the DAC, convert your file to a.very high bitrate MP3 format and put them on a USB flash drive to plug into your head unit.

 

[Haywood]

Honestly, the impact of lossy-to-lossy transcoding is going to be vastly bigger than any difference between DACs.

 

[Flint]

Honestly, the impact of lossy-to-lossy transcoding is going to be vastly bigger than any difference between DACs.

I don not believe that to be true 100% of the time. A good transcoder will render the compressed audio into a high resolution 24bit format using significant oversampling and effective interpolation then encode that into a different lossy format, and depending on the loss-level, it should sound similar or identical to the original rendered file.

Don't get me wrong, it isn't as good as not transcoding or using a FLAC file in the first place, but different analog sections or poorly clocked DACs can cause more audible distortions.

 

[MatthewB]

The reason I'm concerned is there is a lot of talk that the first generation iPods had the Wolfson DAC's which my iPod 5 gen has compared to the nano which has the cirrus DAC also the iPod 5 is basically a portable hard drive while the Nano is basically a souped up flash drive. I can tell a slight difference in the sound quality between the two but was wondering if it was the iPod or car built in DAC doing the transcoding which was making the bigger impact.

 

[Haywood]

Honestly, the impact of lossy-to-lossy transcoding is going to be vastly bigger than any difference between DACs.

I don not believe that to be true 100% of the time. A good transcoder will render the compressed audio into a high resolution 24bit format using significant oversampling and effective interpolation then encode that into a different lossy format, and depending on the loss-level, it should sound similar or identical to the original rendered file.

Don't get me wrong, it isn't as good as not transcoding or using a FLAC file in the first place, but different analog sections or poorly clocked DACs can cause more audible distortions.

Can you recommend any good software? I used iTunes to transcode AAC tracks my wife bought from Apple to MP3 for playback in the car and they definitely sounded worse. Noticeably so.

 

[Flint]

I dont know any of the free audio programs. I use Wavelab from Steinberg, which is a professional tool. I also license the Frauhoffer MP3 encoder to ensure the highest performance when encoding.

 

[Haywood]

I dont know any of the free audio programs. I use Wavelab from Steinberg, which is a professional tool. I also license the Frauhoffer MP3 encoder to ensure the highest performance when encoding.

How does Frauhoffer compare to LAME?

I've been playing with XRecodeII and Exact Audio Copy, but have not tried lossy to lossy yet. Exact Audio Copy is great for ripping discs to FLAC. XRecodeII is good for transcoding WMAL to FLAC.

 

[Flint]

The best lossy encoders are not free. Frauhoffer invented the usable technology and has been perfecting it consistently ever since, so aside from WMA or AAC, which both are very good, there are no other free lossy compression tools out there which can compete with the for pay versions (if you are doing critical listening to lossy files).