iPad Pro Audio Quality

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iPad Pro. bigger. (12.9" diagonal, 4:3 aspect ratio, 264 DPI 2,732 × 2,048 Retina display, 10 hour battery life, 24.735 oz./701.3g, $800 ~ $1,080.) I got mine from Santa for Christmas; I'd also get it at at Adorama, at Amazon or at B&H. I'd check for accessories at eBay.

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January 2017   audio reviews   Apple   headphones   tube amps   all reviews

 

Introduction

These are measurements of the 3.5mm analog audio output of my iPad Pro playing signals in its Music app.

Few people realize that Apple iOS devices have some of the best audio digital-to-analog converters and low-impedance headphone amplifiers available at any price.

Here are some quick measurements of my iPad Pro made in my laboratory with a state-of-the-art Rohde & Schwarz UPL audio analyzer.

 

Maximum Output Levels

At 0 dBFS at maximum volume setting with various resistive loads:

200kΩ: 1.0355 V RMS @ 0.002% THD.

600Ω: 1.0317V RMS @ 0.002% THD.

300Ω: 1.0275 V RMS @ 0.002% THD.

37.5Ω: 0.968 V RMS @ 0.005% THD.

This is exceptional; almost nothing else has this little THD, and very few portable devices have this much clean output in to low-impedance loads.

 

Output Source Impedance

THe output source impedance measures 1.7Ω from 31 to 20,000 Hz.

THis is flawless, anything less than a couple of ohms is great.

Higher output source impedances lead to frequency response imbalances caused by the varying real impedance of actual headphones with frequency, and also leads to low-frequency distortion when driving real headphones.

The ultra-low output source impedance of the iPad Pro is so low as to stop any of these potential problems

 

Channel Balance

At the maximum violume setting, the chanels matched to within ±0.008 dB, which is excelltnb.

THey matched to within ± 0.02 dB throughout the rest of the volume control setting, which again is excelent.

 

Frequency Response

Apple iPad Pro Audio Measurements

iPad Pro driving a resistive load.

Frequency response is super-flat, +0, -0.025 dB from infrasonics to at least 20,500 Hz.

It's easy to make an amplifier which tests well driving resistive loads. Driving actual headphones is where it gets difficult, and where the iPad Pro excels.

Let's really push it and measure frequency response while driving some real headphones, the 32Ω beyerdynamic T51i:

Apple iPad Pro Audio Measurements

iPad Pro driving the 32Ω beyerdynamic T51i headphones.

YES! The low output source impedance leads to ruler-flat response driving real loads, much flatter than most gear with higher output source impedances. The maximum deviation from flat was +0.13 dB at 101 Hz.

Let's increase the vertical scale just to look more closely:

Apple iPad Pro Audio Measurements

iPad Pro driving the 32Ω beyerdynamic T51i headphones.

Marvelous, better than ±0.1 dB driving a real set of low-impedance headphones. Bravo!

 

Harmonic Distortion Driving 200kΩ

Driving 200kΩ is what we see when using the iPad Pro' analog 3.5mm output to drive the line input of a HiFi system.

Apple iPad Pro Audio Measurements

0.002% THD and harmonic distortion components at 1 kHz at 0 dBFS into 200KΩ at maximum output level.

The harmonic distortion is mostly second-order, just like a tube amplifier. Bravo!

 

Apple iPad Pro Audio Measurements

0.005% THD and harmonic distortion components at 4 kHz at 0 dBFS into 200KΩ at maximum output level.

 

Apple iPad Pro Audio Measurements

0.002% THD and harmonic distortion components at 31 Hz at 0 dBFS into 200KΩ at maximum output level.

 

Harmonic Distortion Driving 300 Ω

Driving 300 Ω is what we see typically when using the iPad Pro' analog 3.5mm output to drive high impedance headphones. The 300 Ω resistive load I'm using is a much easier thing to drive than real headphones.

Apple iPad Pro Audio Measurements

0.002% THD and harmonic distortion components at 1 kHz at 0 dBFS into 300Ω at maximum output level.

The THD driving 300 Ω is just as low as into 200kΩ and harmonic distortion again is mostly second-order, just like a tube amplifier. Bravo!

 

Apple iPad Pro Audio Measurements

0.005% THD and harmonic distortion components at 4 kHz at 0 dBFS into 300Ω at maximum output level.

Again, 300Ω measures the same as 200kΩ.

Apple iPad Pro Audio Measurements

0.006% THD and harmonic distortion components at 31 Hz at 0 dBFS into 300Ω at maximum output level.

 

Harmonic Distortion Driving Real 32Ω Headphones

It's easy to make an amplifier which tests well driving resistive loads. Driving actual headphones is where it gets difficult, and where the iPad Pro excels.

Let's really push it and measure distortion while driving some real headphones, the 32Ω beyerdynamic T51i:

Apple iPad Pro Audio Measurements

0.125% THD and harmonic distortion components at 31 Hz at 0 dBFS driving the 32Ω beyerdynamic T51i headphones at maximum volume setting.

This is extremely good performance for this full-scale torture test. THD is of course much lower at higher frequencies, driving headphones at low frequencies is where this becomes difficult for headphone amplifiers.

 

Apple iPad Pro Audio Measurements

0.017% THD and harmonic distortion components at 31 Hz at 0 dBFS driving the 32Ω beyerdynamic T51i headphones at -20dB volume setting.

This is a much more reasonable level; there it no music at full scale at 31 Hz as tested above.

This is excellent real-world performance — which few portable audiophile products can match at any price!

 

Analysis & Recommendations

As expected, the analog audio output of the iPad Pro is extraordinarily good.

Apple has more smart people and more resources than any other audio company on the planet, so as we see when it comes to audio engineering, the iPhone easily outdoes many so-called "audiophile" products.

For enjoying music, you will probably get poorer performance if you waste your time and money with outboard DACs or headphone amplifiers; the iPhone already has the best there is.

Why do commercial audio magazines tout external DACs and amplifiers? Because that what their advertisers are trying to sell!

The only reason to get an outboard headphone amplifier for use with your iPad Pro is if you have high-impedance (100Ω or greater) headphones like the 600 Ω beyerdynamic DT880 which often require more voltage than the 1V RMS maximum from iOS devices. In this case, you still don't need a DAC; the analog output from the iPhone's 3.5mm jack will probably be better than what you'd get fromo an expensive outboard DAC!

 

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30 January 2017