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Audio quality of Apple Lightning to 3.5mm Headphone Jack Adapter

This adapter has been tested recently with more accurate measurement setup - http://soundexpert.org/vault/dpa.html#apple-a1749

 

Apple adapter A1749

Figure 1. Apple adapter A1749

 

Lightning to 3.5mm adapter (A1749) is a solution Apple offers after disappearing headphone jack from iPhones. The features of the adapter in short:

1. Mass audio product, supplied with every iPhone without headphone jack.
2. Retail price is $9.
3. DAC+headphone amplifier are inside lightning connector (see Fig.2 and the teardown at IFIXIT).

X-ray image of Apple’s A1749 adapter by Creative Electron  Figure 2. X-ray image of Apple’s A1749 adapter by Creative Electron

4. Surprisingly good traditional audio measurements made by Ken Rockwell and Archimago.

 

 

Figure 3. SE measurement procedure is mainly the recording of some test sequences, played by device under test. Standard SE test sequence includes 10 test signals and two hours of various music material.

Recording of SE test sequences through A1749 adapter

 

 

Results of standard SE df-measurements of the adapter:

Df-slide with results of testing A1749

Figure 4. Df-slide with results of testing A1749. Df-slides of various devices can be compared to each other on the Portable players page.

 

The adapter was tested with iPad mini. The latter has been tested earlier, its df-slide is below:

Df-slide with results of testing iPad mini 2

Figure 5. Df-slide with results of testing iPad mini 2, which was used as a host for testing A1749 adapter.

 

Enlarged version of Sine12.5kHz diffrogram from Fig.4

Figure 6. Enlarged version of Sine12.5kHz diffrogram from Fig.4. Vertical “greener” lines show time inconsistency of the output signal. This is how jitter looks like.

 

Conclusions:

(1) Artifact/sound signatures of both the adapter and iPad mini are similar (close Df values and their relative positions, similar histograms). The adapter utilizes the same audio solution that is used in iPhones 4/5/6 and other portable audio devices by Apple.

(2) Vertical stripes on Sine12.5kHz diffrogram in Fig.4 (enlarged version - Fig.6) reveal small time inconsistency of the adapter's output signal (probably, clock generator of lightning interface is the source). High frequency components of a signal are affected the most by such time instability or jitter. Real-life music signal is almost not affected (+0.2dB).

(3) Just for reference, white noise diffrogram of the adapter (Fig.4) reveales steep cut off of frequency response near Nyquist frequency.

(4) Just for reference, in case of the adapter all SE test signals show a bit worse Df values in comparison to iPad mini. Except MOD-SMPTE 1:4 signal, which is reproduced more accurately by the adapter (-3.2dB, additional research needed).

Audio quality of Apple Lightning to 3.5mm adapter (A1749) is almost as good as in-built mobile audio solutions by Apple, though it has slightly worse df-measurements. Mostly due to the higher jitter. But if you listen music you will not hear the difference; it is too subtle to be perceived.

 

 

Appendix

 

1. Diffrograms of 35 tracks of the test set “Variety”, played back through A1749 adapter. They show level of waveform degradation of the musical signal divided into 400ms chunks (one pixel each). Median Df values of the tracks are indicated. Click a track to open in full size for quick comparison with similar tracks from another device. More about diffrograms → Diffrogram: visualization of signal differences in audio research.

All-off
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35
AppleA1749 - Variety - 1 AppleA1749 - Variety - 2 AppleA1749 - Variety - 3 AppleA1749 - Variety - 4 AppleA1749 - Variety - 5 AppleA1749 - Variety - 6 AppleA1749 - Variety - 7 AppleA1749 - Variety - 8 AppleA1749 - Variety - 9 AppleA1749 - Variety - 10 AppleA1749 - Variety - 11 AppleA1749 - Variety - 12 AppleA1749 - Variety - 13 AppleA1749 - Variety - 14 AppleA1749 - Variety - 15 AppleA1749 - Variety - 16 AppleA1749 - Variety - 17 AppleA1749 - Variety - 18 AppleA1749 - Variety - 19 AppleA1749 - Variety - 20 AppleA1749 - Variety - 21 AppleA1749 - Variety - 22 AppleA1749 - Variety - 23 AppleA1749 - Variety - 24 AppleA1749 - Variety - 25 AppleA1749 - Variety - 26 AppleA1749 - Variety - 27 AppleA1749 - Variety - 28 AppleA1749 - Variety - 29 AppleA1749 - Variety - 30 AppleA1749 - Variety - 31 AppleA1749 - Variety - 32 AppleA1749 - Variety - 33 AppleA1749 - Variety - 34 AppleA1749 - Variety - 35
-30.1 -25.1 -25.5 -33.2 -26.6 -26.7 -32.1 -24.3 -24.1 -23.6 -26.8 -22.6 -21.9 -27.8 -35.8 -25.9 -27.9 -25.2 -33.2 -37.9 -31.6 -23.6 -24.6 -21.7 -27.3 -27.2 -24.0 -20.9 -27.0 -26.0 -25.8 -21.1 -34.6 -25.3 -27.9

 

 

2. Dendrogram of similarity of artifact signatures for the portable players.

Dendrogram showing similarity of artifact signatures of tested players

Figure 7. Dendrogram showing similarity of artifact signatures of tested players. The shorter the link between two players, the more similar their artifact signatures. The Spearman distance = 0.1 is critical for relation of Df measurements to subjective scores. For those players which have similar artifact signatures (distance < 0.1) their perceived sound quality correlates well to df-measurements with substantial amount of real-life music material (histogram medians).

 

The similarity dendrogramm is a bit misleading in this case (cophenetic coef. = 0.74). There should be a better instrument for visualization of non-euclidean distances between objects. Until then underlying matrix of distances will accompany each dendrogram (Table 1).

Table 1. Matrix of distances (Spearman) between artifact signatures of the players.

        (1)       (2)       (3)       (4)       (5)       (6)       (7)
 (1) Apple iPad mini 2
(2) HTC Desire C
(3) HTC Desire C (ba)
(4) Shanling M2s
(5) Shanling M2s (HighGain)
(6) Shanling M2s (gradual)
(7) Apple A1749 adapter
          0    0.0619    0.0972    0.0445    0.0446    0.0334    0.0374
    0.0619         0    0.0655    0.0149    0.0147    0.0174    0.1494
    0.0972    0.0655         0    0.0651    0.0651    0.0660    0.1710
    0.0445    0.0149    0.0651         0    0.0002    0.0024    0.1378
    0.0446    0.0147    0.0651    0.0002         0    0.0025    0.1379
    0.0334    0.0174    0.0660    0.0024    0.0025         0    0.1229
    0.0374    0.1494    0.1710    0.1378    0.1379    0.1229         0

 

From the table, A1749 adapter can be safely compared to iPad mini 2 using df-measurements because they have similar artifact signatures (distance = 0.0374 < 0.1). Comparison of A1749 with other tested devices is questionable as their artifact signatures differ to greater extent (additional research needed).

 

Comments
Roland
Very interesting – thanks very much!
I have an old iPod classic and have an adaptor to take the audio out of the dock straight to a 3.5mm jack which I plug into an external portable amplifier for my headphones. The audio is much better than straight from the 3.5mm socket on the iPod, I think because it bypasses the iPod headphone amplifier and just gives the analogue audio straight. I don't know if you have any view on this, or if there might be an equivalent way of doing this from a modern iPhone? I guess it would be the equivalent of sticking it in a (non-DAC) dock.
RC
Posted on 1/11/20 11:48 PM.
John
What I like is that the Lightning connector provides an option to use an external DAC in the quality that you choose. The Apple dongle provides at least as good as what the analog 3.5 jack did previously.
Although you do have to deal with that dangling dongle if you use Wired headphones. Probably not worth it given a good pair of Bluetooth headphones would be easier to work with. But certainly, if you're an audiophile, you could buy a better DAC and use really good headphones and gain improved quality.
Especially now that Apple does allow Lossless playback with Apple music.
Posted on 2/6/22 1:43 PM.
Audio-Transparency Initiative