[doomlordis]

Found this quite revealing on the subject

http://members.brabant.chello.nl/~m....surements.html

Seemd that the ipod is lacking bass through headphone out but line out is fine.

 

[bangraman]

Sennheiser HD650 + Zu Cable + totally overkill size converter plugged directly into switcher. HD650 is a 300 ohm impedance phone.

No difference.


Sony MDR-V700DJ plugged directly into switcher. MDR-V700DJ is a 24 ohm impedance phone.

This is a very interesting result: There's a major difference, with the Line Out sounding quieter, less bassy and 'finer' (although whether it actually displays finer sound traits are another matter. I think it's due to the lessened bass).


I would therefore put it to you guys that the difference made by the extra components for either the Headphone Out or Line Out is in the low input impedance area... i.e. specifically dealing with portable headphones. At high input impedances, even starting from 300 ohm phones, it does not seem to make any difference.


Referring to the previous post by doomlordis, I would summise that had they not made the changes to the headphone out that Apple did, the iPod would have ended up sounding even more anaemic in the lows.

 

[lindrone]

Quote:

Originally Posted by bangraman I would therefore put it to you guys that the difference made by the extra components for either the Headphone Out or Line Out is in the low input impedance area... i.e. specifically dealing with portable headphones. At high input impedances, even starting from 300 ohm phones, it does not seem to make any difference.

Interesting, since I own no high-impedance headphones at all anymore (everything I own is 40 ohms and below)... That might be the reason why I've always noticed a difference?... Hmm....

So what does this mean though? Is the line-out a true line-out, or is it just a path without the volume control?


Quote:

Referring to the previous post by doomlordis, I would summise that had they not added the extra bits to the headphone out that Apple did, the iPod would have ended up sounding even more anaemic in the lows.

It's outdated anyway, that test is often referred to, but was done on a 3rd gen iPod. 4G iPod do *not* sound the same as the 3G.

 

[bangraman]

Just so that lines don't get crossed, when you amp the iPod, the load presented to the iPod is the Line Input impedance of the amp, not the phones.


As the above test indicates, there's clearly a difference in the two outputs, but only in low input impedance ranges. This would seem to suggest that the Line Out is a volume fixed version of the Headphone Out, without the components that make the Headphone Out more compatible with low impedance phones.


I ought to mention that I have run a similar test as what I've outlined in this thread, although on a more informal level, on the iPod Mini with the same results. That is something I can't really prove but at that time with what I had I could not tell any significant difference between Line Out and Headphone Out after initial volume matching.

 

[DHT 2A3]

I remember reading an article when the 3G iPod was introduced, in which they measured distortion, and the conclusion that the cleanest signal from the headphone out was at one or two 'clicks' backed off from max volume. Of course now can't find the review, but it was in the Spring of 2003, maybe via iPodlounge. Stereophile also did extensive testing, but I don't recall those measurement results.

 

[gerG]

I want to reiterate that the differences that I heard were mainly in the imaging, and were quite apparent. I was very careful with level settings. When I did the test I also did cable swaps to make certain that there was no contribution from either side of the switcher. I even did deliberate level mis-match to see if that is what I was hearing. It was not. The image detail changed. It is most apparent in source material with clearly defined instrument positions. I do not know what the input impedance of the Grace is, but I would assume that it is typical of many amp inputs. Headphone impedance is not relevant.

It is rather funny, because when I bought the adapter for line out I was convinced that this was all hype, and the "line out" was just a fully amped output. I don't believe that anymore. Anybody know how the volume control in the ipod works?

I am curious enough now to try the check again, with a new twist. Stay tuned.


gerG

 

[Fleet]

Now, I'm no expert but I figured I'd share my thoughts in case other "non audophiles" are reading.

I have an Ipod Mini and a Total Airhead Amp. I did my testing with both Etymotic Er-6i and Sennheiser Px-100 headphones.

To get a line out, I used a Monster Cable adapter I have for my car. It plugs into the bottom of the Ipod and has a lineout mini plug as well as a car adapter. It works well with my car setup for the Ipod.

So, the first test I did was comparing sound quality between headphone jack and the lineout through the amp with the PX-100. I set the headphone volume to about 90% of capacity. I listened to Queensryche, "Silent Lucidity" while switching the plug between the 2.

Result: I can't hear a difference

Next, same deal with the Er-6i. Now, these are only about a week old, so not broken in well. This time it was Megadeth, "Almost Honest". (Sorry if you don't appreciate my taste in music)

Result: I can't hear a difference

Both Mp3 files were encoded with MusicMatch Jukebox at 160KB/s.

I have personally been debating whether to purchase a lineout unit from sendstation or sik, but have decided to save my money. There's just no bang for the buck with my lower end setup.

I definately do recommend an amp with either the PX100 or Er6i's though.

Hope this helps.

 

[Brian Beck]

Let's have a look at the chip that Apple uses! The block diagram of the Wolfson WM8731L, which I hear is used in recent iPods, shows that the line outputs are taken from points in the chip prior to the volume control and the final headphone amplifiers. Not surprisingly, into an appropriately high impedance (such as with an external HP amp) the line amps ought to be superior, since they bypass the additional circuitry. And, of course, the line outputs weren't designed to drive low Z headphones directly. With the headphone output the bass droop with low Z headphones is almost certainly due to having to use coupling capacitors to block DC. The higher the Z of the headphone, the deeper the bass should go. There just isn't much room in an Ipod for big film caps! With my 300 ohm Senn 600s, the HP output sounds mighty fine with just enough volume for me 90% of the time. Will be trying my own tubular HP amp soon for comparison.

 

[bigshot]

Heavy Metal music isn't the right thing to check this with. You need a sample that is not compressed to make it sound louder, has a great deal of very sharp dynamics- soft to loud, and no built in distortion (ie: fuzzy guitars).

See ya
Steve

 

[raisin]

Great first post, Brian.

 

[gerG]

More results.

Bottom line, I found the cause for much of the difference (not all) and fixed it. Mini-plugs suck at best, and any discussion of audio quality when the signal is going through one of those things is of marginal value.

Details:

This time I set up with a speaker system. I used a PS audio preamp to switch between 3 inputs, 2 for the ipod and one feed from a Sony S9000 as a reference to keep me grounded. The preamp uses a rotary switch, so I could click between inputs and easily forget which was which. Output went to an active crossover feeding 2 Carver amps, each of which drive one Prelude tower and one Nuclear sub (bi-block configuration).

I started off with Acoustic Alchemy "Reference Point" (seemed appropriate). I stock my ipod with AAC files at 256 kbps. Initial results were much the same as with the headphones. The difference was immediately apparent, but it took a minute or two of studying the music to discern what was being affected. I did numerous cable swaps and hooked them up blind each time. I nailed the headphone output every time for about 5 cable swaps. Then something funny happened. The difference became more subtle and harder to pinpoint. Since I had been swapping cables, I pulled both of the ones connected to the ipod, cleaned the connectors at both ends, added contact enhancer, and re-installed. I didn't clean the sockets yet. Differences got even more subtle. I can still track down the HP output blind, but I have to switch back to the reference to do it.

What I am hearing is a slight smearing of the image (spatial) with a sort of a reverb haze added (temporal). It is very much like a reflective surface behind the musicians. Actually both of the ipod outputs have this compared to the reference, but the phone out has the more reflective wall back there.

At this point the difference between the outputs is getting very small. Without a direct A/B test I doubt that I could figure out which was which. For casual listening I could go with either. For serious listening, well, I would not be using the ipod for that.

The remaining question for me: is this the electronics, or just those damned connectors? This may seem like a trivial issue, but it is still relevant to the question at hand. If the headphone output degrades with daily use (I work out with my minipod) then the docking port may still offer a significant sonic advantage.

Oh, one other revelation: the phone output and line output are 180 degrees out of phase. Cross connecting to match levels will not work on speakers!

I still encourage you to do this test for yourselves, on your own gear, with your own ears.

I also encourage open revolt against the pox of the mini-plug!


gerG

 

[bangraman]

I still say you're probably not setting the volume to match the Line Out, or that with the iPod Mini there is a difference... I can't be sure about this. There's only an involved way to know this for sure, but instead of trying to hear a difference I went at it the other way, which is at what HP volume level is it most similar? At a certain volume level it is the same. At other levels the output is different and you can read a lot of things into that difference.

 

[Syzygies]

I wish that everyone who weighs in on this thread would specify the bitrate and compression scheme they're using. I've been less "scientific" about this, but very frequently switching setups and listening critically.

I have many headphones, including Grado SR80's, an ancient Stax electrostatic rig w/ amp, and Etymotic 4p's. My current headphone amp is an upscale railsplitter CMoy, so I'll have better insights into this when I build my PIMETAs.

I've always considered the general acceptance of 128 kbps audio a ghastly phenomenon that will pass like the dot matrix printer era I lived through. Print was better before, and is better now. Sound was better before, and will be better when we move back to CD-quality audio, will be much better when we move to 24 bits.

My oldest rips are 320 kbps MP3's. More recently I rip to Apple Lossless and reprocess to 320 kbps AAC's, saving both. I'm glad I did. With everything before my Etymotic earphones, I mildly preferred lossless to AAC to MP3, but not enough to rerip my MP3's or give up capacity on my iPod to carry only lossless.

With my Etymotic 4p's, I hear what's on the CD, for better or worse. There is often magic in good recordings. That magic disappears if I do any single thing wrong, such as: Have the arrogance to solder a 4p to 4s converter using RadioShack grade resistors. Use a perhaps defective SendStation PocketDock for my line out, rather than an Apple Dock. Use AAC or MP3 rather than Apple Lossless. So now I only carry around lossless. I swap music onto my iPod the way I used to swap CD's into my car.

I'm pretty far down the food chain in gonzo high-end audio, but we've all heard this "weakest link" theory before, and we all know it's true. Your sound is probably limited by your headphones, or your connectors. It's certainly limited by the source recording. If you're using lossy data compression, it's certainly limited by the compression.

To reach the question under debate, using Etymotic 4p earphones and Apple Lossless compression, I hear magic through line out that is somewhat missing through headphone out. Using other headphones and lossy compression, I can't hear a difference, when I set the headphone volume somewhat shy of max. (I settled naturally on this, agreeing with what several of you assert.)

In other words, I think there's no debate here, every one of you is right.

 

[KenW]

Quote:

Originally Posted by bangraman No. I mean they sound the same. I've repeated this test with the HD650+Zu, a prototype high-end amp and an audio switcher and the result is the same. I'll do it with the Supermini and an MDR-V700DJ if you like! The key is setting up the headphone output volume properly, because if you don't do this you WILL hear a difference. The SRM-007t makes it very easy to get relative volumes right as it allows effortless switching between inputs. As I've said before, in my iPod use the main reason to be of the Line Out was that I didn't have to blow out my eardrums when I connected the E5 (or any efficient pair of phones) after unplugging the amp and forgot to reset the volume. As a caveat, the input impedance of the amp will of course affect how the sound comes out. If the amp for some reason has a very low input impedance (possibly an amp optimised to amp a Headphone Out signal) then what you'll hear may be different.

Dang it! Just when I'd put amping the karma out of my mind, I see this thread and post. Aaarrgghhh!

 

[bangraman]

Quote:

Originally Posted by KenW Dang it! Just when I'd put amping the karma out of my mind, I see this thread and post. Aaarrgghhh!

If you're saying what I think you're saying, there's no guarantee that the Karma's headphone out works well with the loads that an amp imposes just because of what I said. Many portables sound pathetic when amped through the headphone out.