Apple Music with iPhone and External USB C DAC: Bit-Perfect or Altered Playback?

[HalSF]

I use Apple Music streaming on MacOS via SMSL and Schiit DACs, and on iOS and iPadOS via the Fosi DS2 DAC/Amp. It sounds great with both lossless and hires sources.

Semi-paranoid musings about Apple somehow throttling or degrading audio quality and failing to deliver the bitrates it labels on the tin are sheer FUD. It’s true that operator error can mess things up, but if you pay attention it’s all good.

In general 99%+ of streaming audio quality discussion (mine included) is purely subjective, and people opine without recourse to any kind of objective measurement and testing. Solid objective comparative measurement/testing of sound quality on the major streaming platforms is virtually nonexistent. It’s sort of astounding this far into the multi-billion dollar streaming era that this is the case, but here we are.

 

[stefanovesa]

my tests with iPhone 16 and iOS 18.5 suggest that:

Apple Music App (I mean the App when playing local lossless ALAC files, not the Apple Music service) is NOT bit-perfect. If it is a bug or intentional I don't know.

For testing I've used RME bit-perfect files and RME ADI-2 DAC FS connected to iPhone.

Sampling rate is auto changed but the good stops here.
16 bit files simply do not pass (why?)
24 bit files pass at 16 bit only
32 bit files rapidly switches between 16 to 24 bit, I mean that the display output flashes between the two values.

I have to check with iOS 26 if anything changed. Can e the particular test files used? I do know, I have no other ways to check.
I simply abandoned Music app for Onkyo Music Player

with iOS 26 the behaviour is the same, for some reason the bitrate is truncated or the test files are inconsistent, I do know.

 

[mermayer]

Semi-paranoid musings about Apple somehow throttling or degrading audio quality and failing to deliver the bitrates it labels on the tin are sheer FUD.

I have verified this: Apple Music Lossless and active crossfading (iPad Air M3, RME ADI-2 DAC).
The song starts at 48kHz and about in the last third, the sampling rate changes to 44.1kHz. I hear a dropout and the display in the DAC changes to 44.1kHz. However, the display in Apple Music remains at 48kHz. The song fades into the next one, which has a sampling rate of 44.1kHz. This is then also displayed correctly in Apple Music. This always happens when the next song has a different sampling rate.
A bug or a feature? Very strange.

 

[mermayer]

To be clear: i guess iOS26 with „Automix“ enabled will lead to a fixed sampling rate as mixing tracks with different sampling rates wouldn‘t be possible then…But i didn‘t try that yet.

No

 

[stefanovesa]

I have verified this: Apple Music Lossless and active crossfading (iPad Air M3, RME ADI-2 DAC).
The song starts at 48kHz and about in the last third, the sampling rate changes to 44.1kHz. I hear a dropout and the display in the DAC changes to 44.1kHz. However, the display in Apple Music remains at 48kHz. The song fades into the next one, which has a sampling rate of 44.1kHz. This is then also displayed correctly in Apple Music. This always happens when the next song has a different sampling rate.
A bug or a feature? Very strange.

Have you had the chance to test with RME bitperfect wav files?

in case you do not know, go to https://rme-audio.de/adi-2-dac.html and scroll until "bit test"

I'm puzzling without rest why Apple Music fails 16 bit and 24 bit bitperfect tests. Other Apps work just fine.
32 bit files are expected to fail because Coreaudio stack is 32 bit FLOAT and cannot render 32 bit audio files if not bypassed and Music doesn't bypass it

 

[HalSF]

I have verified this: Apple Music Lossless and active crossfading (iPad Air M3, RME ADI-2 DAC).
The song starts at 48kHz and about in the last third, the sampling rate changes to 44.1kHz. I hear a dropout and the display in the DAC changes to 44.1kHz. However, the display in Apple Music remains at 48kHz. The song fades into the next one, which has a sampling rate of 44.1kHz. This is then also displayed correctly in Apple Music. This always happens when the next song has a different sampling rate.
A bug or a feature? Very strange.

I don’t use crossfading and don’t experience dropouts with Apple Music switching file rates between songs using the SMSL D-6S or the Fosi DS2.

Sound quality generally seems excellent to me across the range from lossless to hi-res.

 

[mermayer]

Sound quality generally seems excellent to me across the range from lossless to hi-res.

Then try it with lossless and crossfading. You'll get the same result. Either apple is cheating with the sampling rates and these are not native but artificially generated or the Apple Music player has a bug because the sampling rate changes in the middle of the song and not during the crossfade.

 

[voodooless]

I find it highly unlikely that Apple Music would change the sample rate mid-song. When using crossfade, the new song will have the same sample rate as the previous one, otherwise, it cannot mix the two sources. Only when you pause or stop the music does it possibly switch to the correct rate.

If you want bit-perfect, don't use crossfade.

 

[HalSF]

Then try it with lossless and crossfading. You'll get the same result. Either apple is cheating with the sampling rates and these are not native but artificially generated or the Apple Music player has a bug because the sampling rate changes in the middle of the song and not during the crossfade.

I’m not interested in crossfading and would selfishly prefer to avoid this bug, assuming it’s an Apple Music bug and not a DAC thing.

 

[TTT15]

? Just turn cross fade and sound check off in Apple Music app settings

 

[palm]

my tests with iPhone 16 and iOS 18.5 suggest that:

Apple Music App (I mean the App when playing local lossless ALAC files, not the Apple Music service) is NOT bit-perfect. If it is a bug or intentional I don't know.

For testing I've used RME bit-perfect files and RME ADI-2 DAC FS connected to iPhone.

Sampling rate is auto changed but the good stops here.
16 bit files simply do not pass (why?)
24 bit files pass at 16 bit only
32 bit files rapidly switches between 16 to 24 bit, I mean that the display output flashes between the two values.

The RME documentation mentions that iOS supports 24 bits only. I can’t test right now but like I mentioned earlier in the thread the test passed, and your test is actually OK too. There is most probably just 0 padding on 16 bits files. What’s important is that you can send 24 bits audio signal at any sampling rate without any alteration.

 

[stefanovesa]

The RME documentation mentions that iOS supports 24 bits only. I can’t test right now but like I mentioned earlier in the thread the test passed, and your test is actually OK too. There is most probably just 0 padding on 16 bits files. What’s important is that you can send 24 bits audio signal at any sampling rate without any alteration.

You are right, 32 bit is not supported by iOS, but I said that actually 24 bit do not pass. E.g. with Onkyo Music Player it passes. I've filed a bug to Apple but I think that the issue is too marginal and difficult to reproduce, due to the absence of bit check routines in the most part of the DACs on the market.