READ THIS: Serious flaws in ipod classic

[jook]

Quote:

Originally Posted by Bob Mahoy /img/forum/go_quote.gif I am not agreeing or disagreeing or confirming or denying that this information is correct. I am simply acknowledging its' existence so that you all can make a decision on your purchase from a few more sources. So I'd really appreciate it if you stopped flaming me.

Just in case there was some misunderstanding - I wasn't flaming you, and neither do I see anyone else in the thread doing so. My comments were all targeted at the author of the webpage posted, and I question the way he is presenting things and cross-posting on many forums as if it was fact (he links to them all on his page), when it seems questionable (and he even recognizes the problems in his measurements). I don't blame him so much as think it unwise.

 

[mirumu]

I retested again after applying the new 1.0.1 firmware update for the iPod Classic. The test was run multiple times and I got the same result each time. The regenerated graphs didn't seem to be worth posting them as they look exactly the same as the graphs from before the update. Looks to me like this update has not had any effect on the sound that is measurable in these tests.

 

[Buckster]

in that case- if you were in my shoes - for the sake of £20 pounds, and SQ being the only consideration really (apart from space) - would you keep a 6G or replace it with a 5.5G ?

thanks, Mark.

 

[Dzjudz]

So, does the new firmware make this thread pointless?

 

[mirumu]

Quote:

Originally Posted by Buckster /img/forum/go_quote.gif in that case- if you were in my shoes - for the sake of £20 pounds, and SQ being the only consideration really (apart from space) - would you keep a 6G or replace it with a 5.5G ?

I'm afraid I can't honestly answer that for you as I've never heard the 5.5G. What I can say is that in my opinion the 6G iPod sounds very good and based on the graphs would appear to have slightly better bass response than the stock 5.5G. If you would ever consider iModding the unit then really the 5.5G is the only choice.

 

[mirumu]

Quote:

Originally Posted by Dzjudz /img/forum/go_quote.gif So, does the new firmware make this thread pointless?

The new firmware has not made the measurements look any better so I would say no.

 

[rhymesgalore]

@mirumu:

Out of my own curiosity, since i'm not able to make my own measurements, could you perhaps - if you find the time - measure a frequency response graph, with the iPod EQ set to "more highs" (don't know the exact term in english right now, since my iPod is in service, and i usually have it running in german)

I'm just curious what a treble boost really looks like......

 

[sno1man]

Well this thread and that article will be the "reference" for all of the "but i'm not buying a 6g ipod because of the poor frequency response/sound/phase" posts that will pop up on this board for the next year. Perfect for the apple bashers........

There are so many variables in the chain. The vast majority of peoples own ears are not linear or flat in frequency response. For that matter a bit of ear wax in one ear can cause a "phase shift"

Trust your own ears. I do think the 6g is an improvement over my 60g 5g ipod. I'm happy , i'm keeping it.

And yes i dont use lossless but high bit rate VBR AAC, and my phones are ety 4p's, etc. It is a portable after all

 

[mirumu]

Quote:

Originally Posted by rhymesgalore /img/forum/go_quote.gif @mirumu: Out of my own curiosity, since i'm not able to make my own measurements, could you perhaps - if you find the time - measure a frequency response graph, with the iPod EQ set to "more highs" (don't know the exact term in english right now, since my iPod is in service, and i usually have it running in german) I'm just curious what a treble boost really looks like......

Here you go. This is from the "Treble Booster" EQ setting. It's not really as flat as I would have expected and it seems to have quite a dip at 7KHz. Looks like it starts climbing at 500Hz too so it's really more of a midrange and treble booster I'd say.

 

[rhymesgalore]

Thanks a lot. Much appreciated!

And it sure does look a bit strange. But it also shows that there's a boost of 1.3-1.4db at way lower frequencies than 19khz, so it really makes you wonder, how someone could hear 0.1db at 19khz.

 

[mirumu]

Quote:

Originally Posted by rhymesgalore /img/forum/go_quote.gif Thanks a lot. Much appreciated! And it sure does look a bit strange. But it also shows that there's a boost of 1.3-1.4db at way lower frequencies than 19khz, so it really makes you wonder, how someone could hear 0.1db at 19khz.

The author of the original article has updated the page with an appendix which would seem to be in response to our comments here. He provides some evidence suggesting that a 0.1db or 0.2db difference is indeed audible. At the very least he suggests that according to published information this behaviour is "within the threshold of audibility". While I'm not for a moment about to just dismiss such talk offhand, I still do have trouble believing anyone would pick such a difference at 19Khz. The treble still appears boosted even as low as 10Khz and maybe at this level such a boost might be audiable but it's also less than 0.1db at that level in the graphs from what I can see.

I've been listening to my 6G iPod tonight through my STAX SR-X MK3 headphones to try and get a feel if the phase shift is at all audible. Essentially I'm trying to pick frequencies that are supposed to be in sync which played out of sync by the iPod. So far I can't find anything like this. I feel it's safe to say if it is there it's very very small, anyone worrying about things like cymbals arriving after the drumbeats throwing the timing off has nothing to worry about, it's definitely orders of magnitude smaller than that. I'm thinking the only way I might be able to pick it is in instrument timbre or a lack of spatial information. I've switched to mostly acoustic and piano music to try and focus on these areas but as of yet I still can't hear anything like this. What is coming through though is how clean the output of the 6G is. The very low noise floor and good resolution makes it sound surprisingly good with electrostatic headphones.

 

[me7]

Is it possible to reproduce the impulse response shift on a PC via software? This would allow an easy ABX for everyone.

EDIT: Just saw an interesting post on the apple forum. What do you guys think about that?
Quote:

As an audio engineer I must disagree with your conclusions regarding severity of the issue. The variations found (0.1dB) are simply too small to amount to anything significant. 1dB is DEFINED as the smallest volume change that a human can perceive, and 0.1dB is a variation far smaller than batch discrepancies in any group of identical speakers or headphones you care to name. Furthermore, the so-called “incorrect timing response” is EXACTLY what one SHOULD see given a small change in treble response - this is systems engineering 101, folks. The time and frequency domains are different reflections of the same behavior. I will add that this “timing response” is far more linear and of a smaller magnitude than any mechanical device (speaker, headphone) you will find on the planet. These mechanical necessities will simply swamp any small variation in the electronics. As to spatial effects - I will step into deeper waters here and state that any that exist in 2 channel recordings are subject to an awful lot of much larger forces, such as room acoustics, headphone behaviors, and a lot of psychology. Spatial data simply is so poorly represented in 2 channel audio that when it seems to work it is often as not a fluke - the data just isn’t there in a reliable form. When we have recordings that actually represent multi-channel, multi-direction room reflections and multi-channel, multi-direction playback systems we might have something, but not today. So, is the iPod perfect? No. But I sincerely doubt that these changes are in fact audible, even given good quality headphones. I have listened to far too many pieces of gear to believe that.

 

[bigshot]

Quote:

Originally Posted by mirumu /img/forum/go_quote.gif The author of the original article has updated the page with an appendix which would seem to be in response to our comments here. He provides some evidence suggesting that a 0.1db or 0.2db difference is indeed audible.

The definition of "decibel" is the amount of difference that one can discern using test tones. So .1 would be 1/10th of audible. Compare using music instead of test tones and the threshold of discernability goes up to about 3dB.

Too often, numbers get thrown around with absolutely no regard for their meaning. Equipment is often rated as being +/-3dB of flat from 20Hz to 20kHz. If the variance is as low as .1dB, that's pretty doggone good frequency response. This doesn't even take into account the fact that many people can't hear 19kHz and there is no musical instrument (aside from synths) that operates anywhere near that range.

It's amazing that this has generated so many posts. I would think most people would look at those numbers and laugh and move on.

See ya
Steve

 

[akira281]

Quote:

Originally Posted by me7 /img/forum/go_quote.gif Is it possible to reproduce the impulse response shift on a PC via software? This would allow an easy ABX for everyone. EDIT: Just saw an interesting post on the apple forum. What do you guys think about that?

and the response ...

"Dear Brad,

I fully agree that 0.1dB on its own is not a reason for concern. It is my experience, and the experience of many other audio engineers that a rising curve from 20Hz to 20kHz with 0.2dB CAN give audible results, depending on the reason (e.g. think of the differences in the passband of a Butterworth and Bessel filter). I've heard many many cases supporting this, also in my own audio engineering (e.g. developing a subband rejection filter for a DAC).

The difference in measured phase response cannot be explained simply from the frequency measurement as you state. I've calculated a minimum phase response from the frequency response (brown curve - and yes, that shows a relation like you say), and it is completely different from the measured response. This hints at non-linear behaviour of the circuitry or signal processing. Hence, the output of the iPod is not a minimum phase system. I would suspect this to be clearly audible, as confirmed by many articles in the AES (depending on their context).

Mechanic devices, despite their shortcomings, exhibit linear properties and are minimum phase systems, and their phase response can be deduced from their frequency response. Their shortcomings can be coped with by proper engineering. The fact that a certain device is the weakest component in the audio chain (e.g speakers with typically 3 to 6 dB deviations on-axis) doesn't imply that small variations in the source components (digital players, amplifiers) are not audible, or not significant. It only takes more than a frequency curve to find what is relevant, and what is not relevant. Let's just mention jitter as an example, it clearly affects spatial response, but it is hardly measurable with classical measurements.

My claim is not about the iPod being perfect or not. I was disappointed to realize that my upgrade from a 5G to a 6G implied a step backwards in sound quality. LESS spatial information (the difference between music around you or in your head WITH THE SAME HEADPHONE), an electronic haze to the sound, and less harmonic content. I tried as best as I could to find some reasons, and measurements show the new iPod deviates quite a lot from the old one, and might hint at the root cause. The root cause, unfortenately, is impossible for me to dig into, with no access to the electronics and firmware, and therefore is in the hands of Apple right now.

Let me also state that despite the lesser sound quality, the 6G is still a good device in many aspects, and due to the fact that it is introduced quickly, needs some attention with respect to stability and other improvements. Where I would give the 5G a 9 out of 10 for sound quality, the 6G gets a 6 out of 10. If sound quality is of main concern, I would certainly recommend a 5G right now, otherwise I would recommend a 6G, it is a nice product in all other aspects.

Hence, I'm enjoying my 6G, but just less than my 5G with respect to sound, and I hope Apple can pay a bit attention to it. My own experience tells me that a slight filtering in the top end would already solve quite a bit. I have no clue about the cause for the group delays.

Marc "

 

[Prozakk]

I'm just going to get my 5.5g 80gb iModded. Problem solved.