« Back

Audio quality of Apple Lightning to 3.5mm Headphone Jack Adapter

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
No comments yet. Be the first.

 


 

For almost 20 years SoundExpert is the home for innovative audio measurements and research. Newly developed listener-centric audio metric combines instrumental measurements with listening assessments and helps to perform both more efficiently.

Since 2001 more than 10 000 volunteers participated in distributed blind listening tests on Soundexpert website. Sound quality ratings of 100+ codecs were computed thanks to their time and efforts. You can still take part in them.

Recently we developed a new method for instrumental measurements of audio equipment. It is based on the new audio metric and helps to examine technical performance of an audio device in great detail. Furthermore all audio devices can be grouped according to their sound signatures. The measurement procedure was fine-tuned during two years of beta-testing with 30+ portable devices. Now it is mature enough for production environment. First few tested players can be found on Portable players page.

I hope this new audio metric will attract more audio engineers and enthusiasts as it opens new field of audio research where objective and subjective are not separated anymore. Further advance in the research requires many more different audio devices to be tested - a serious challenge for our non-commercial research project. Fortunately portable players are good test subjects for this research, even the old ones. That's why I need some help from our volunteers again. If you have such old/previous/ex digital portable audio player or a smartphone that was marketed as "HQ audio inside", if it is fully functional but not in use anymore, please, consider donating it to SoundExpert. Its df-measurements will appear on the portable players page. Then it will be either kept for research purposes or sold off supporting the project additionally (or given away to some music lover if it can't be sold for some reason). I'm going to refund your postal expenses but can't confirm this right now. Please, contact me for further arrangements.

Manufacturers of portable devices can order df-measurements for their products. The cost of the work will be equal to retail price of the device. I will buy it and perform standard df-measurements. If you decide I will not publish results during a year.

Today building a comprehensive audio quality map of various audio devices on the market can be done by ourselves - audio consumers. And it's not hard indeed. In the end this will free up some time for listening and discussing Music, not technology )).

Thanks,
Serge Smirnoff
SoundExpert Founder