[Trenn]

Quote:

Not sure how noise at -120 dB instead of -145 dB is an issue for audio intended for human listening.
 
Unless you specialize in listening to amplified silence.

 
 
Those are the level at each frquency. You need to square and then sum/mean and then square root each level to arrive at the final level. If you do that, the ipod playing mp3 looks to have about 13 bits (best case) signal to noise ratio in the 20 to 20 KHz bandwidth. Not exactly hi fi

 

[stv014]

Besides the information about that measurement being rather limited, 13 bits is more "hi fi" than most people would think (compare this and this to get an idea of how much it degrades the sound if it is quantized from 24 to 13 bits with dithering), with analog gear that was considered "hi fi" in the past, an A-weighted SNR of ~80 dB was very good performance. But if the measurement is of the "noise floor" of lossy compression, I am not sure it means much, unless the iPod for some reason does not decode the file correctly.

 

[bigshot]

All iPods sound the same... Flat response, free of distortion and noise. The specs vary a tiny bit from model to model, but it started out with audibly perfect sound with the first model, so it can't get audibly better.

 

[jaddie]

Quote:

All iPods sound the same... Flat response, free of distortion and noise. The specs vary a tiny bit from model to model, but it started out with audibly perfect sound with the first model, so it can't get audibly better.

Bingo.  
 
The only differences I've found is how clean the EQ settings are.  My iPod 5th can be audibly distorted using any EQ settings (not volume dependent either), but my Nano is pretty clean.  EQ off, they're all great.

 

[Achmedisdead]

Quote:

All iPods sound the same... Flat response, free of distortion and noise. The specs vary a tiny bit from model to model, but it started out with audibly perfect sound with the first model, so it can't get audibly better.

I wouldn't say exactly the same, but close. There's a little bit of a difference between my 5.5 with its Wolfson chip and the newer Cirrus-equipped models, like the Classic 7G and Touch 4G , and Shuffle 4G that I had. Assuming one has decent headphones, they all sound good though.

 

[bigshot]

I have iPods with both chips and they sound identical. My CD player sounds identical too. They all have the same specs, so it would be surprising if they sounded different.

 

[Achmedisdead]

Quote:

I have iPods with both chips and they sound identical. My CD player sounds identical too. They all have the same specs, so it would be surprising if they sounded different.

Do you have a link to measurements of a 5.5G vs.a newer Cirrus model? Or specs of them? Don't get me wrong , the difference is not huge, but it is there.

 

[bigshot]

There's a chart on the Wolfson site that lists specs for their chips. The one that corresponds with the one that is in older iPods is well over the line to audible transparency. Ken Rockwell's recent test of the iPhone show it well over the line too. There may be differences in numbers here and there, but they're below the thresholdof perception.

 

[scuttle]

Quote:

There's a chart on the Wolfson site that lists specs for their chips. The one that corresponds with the one that is in older iPods is well over the line to audible transparency. Ken Rockwell's recent test of the iPhone show it well over the line too. There may be differences in numbers here and there, but they're below the thresholdof perception.

 
The differences may well be imperceivable, but the DAC chip spec by itself means very little - actual DAC circuits often deliver much lower performance than the potential of the chip.

 

[bigshot]

Even much lower would be below the threshold of perception. Just do an A/B test against any CD player like I did. First gen, most recent... They'll all sound the same through line out.
 
...and before you ask, yes. Every CD player I've had in the past ten years sounds the same... From a $900 Phiips SACD player to a $40 Coby DVD player.

 

[IPodPJ]

Quote:

Check this out. The charts made me laugh. So much for iPods having a "sound signature"!
 
http://www.kenrockwell.com/apple/iphone-5/audio-quality.htm

 
Great article.  I always thought the iPhone 5 had the best sound quality out of all of them.  (iOS 6 and iPhone 5 functionality and real world use sucks, OTOH, with over 100 bugs I've found that making using it a horrendous experience.)  The Lightning-to-30-pin adapters with the DACs built-in sound even better than the DAC in the iPhone 5 actually.
 
I was pretty impressed listening to the LCD3 out of the headphone output from my iPhone 5, but it sounds nowhere near as clean, spacious, and detailed as my reference system.  Sorry.  And I attribute the quality sound more to the headphones than that of the iPhone's output.

 

[bigshot]

Use a line out dock, and it will be worthy of your reference system.

 

[Trenn]

Quote:

Not true.  It can result in many different improvements in a noise measurement  depending on noise spectrum...which is the point of a weighting network. 
 
After digging around on the quantesylum site, I could find no background information for the test image above.  If there is some somewhere, please post a link.
 
Interesting statement.  How are you "measuring" these figures?  Are you actually generating some form of distortion or are you trying to simulate harmonic distortion by summing sine waves at different frequencies and levels?

 
Take a look at TI or Cirrus ADC data and you'll see A Weighting is always 3 dB better than unweighted. Yes, if your noise floor is hugely distorted that rule won't hold. If your signal of interest isn't 1 KHz that rule won't hold. But for flat noise with a 1 KHz test tone, it's 3 dB. 
 
See the section "Noise Floor" on the page below. The noise floor of an MP3 is substantially higher than a 24-bit file format. If this graph is true, then it'll readily be audible. 
 
http://www.quantasylum.com/content/Home/tabid/40/EntryId/23/Apple-iPod-Nano.aspx
 
For measuring which THD figures I can hear, it's pretty simple to just generate a 1 KHz tone, and then add in a 2, 3, 4, 5, KHz tone at an increased volume and note at which point you can hear the added tone. Try it and report back. It's really hard to hear 2nd and 3rd order distortion, and much much easier to hear 7th order.  

 

[stv014]

Quote from your blog: "The conversion was done by Audacity."
 
There might be the problem. Audacity has a poor, buggy noise shaped dither that does not work correctly with stereo audio, and adds about -80 dBFS (A-weighted) noise. In fact, I even recognize the spectrum of the Audacity noise on your graph. So, the noise floor is most likely not the fault of the iPod, or MP3 compression (you should not use simple THD, noise, etc. measurements to evaluate perceptual coding anyway), but that of Audacity.

 

[stv014]

Quote:

If your signal of interest isn't 1 KHz that rule won't hold. But for flat noise with a 1 KHz test tone, it's 3 dB.

 
The frequency of the test tone does not matter, unless the noise is not uncorrelated to the signal. It is the bandwidth that determines how much lower the A-weighted level of white noise is than the unweighted level. At very low bandwidth, like 5-6 kHz, the A-weighted noise can even be slightly higher.