iTunes 11.0.2-11.0.4 Playback Bitrate

Just downloaded the latest version of iTunes. Noticed a new playback panel:

Seems you can up-sample your content within iTunes using Apple’s SRC. I did a quick comparison vs 44.1K/16bit and preferred the up-sampled playback… I realize that you can’t add data back to the original file, but playing at a higher sample rate will change the digital filtering applied in the DAC.

To allow direct playback of the iTunes up-sampled stream, you need to match the sample rate in the sound control panel. Otherwise, Windows will re-sample the stream to match the setting. This is because iTunes only supports WASAPI SHARED mode.

Having the Hifiduino controller show the incoming sample rate, helps tremendously in the set up and configuration of different audio players and their options.

Here is the Playback panel of the previous version

UNDOCUMENTED FEATURE

Apple has yet to document the new playback panel in the latest iTunes 11.0.2. If you search their website or the help files, there is no mention of this new option. Maybe this is work in progress and there is more to come in newer versions of iTunes. As it is,  it  works straightforwardly by determining the audio output sample bit rate and bit depth during playback.

Since iTunes 10.5, the Quicktime component is not included in the installation [link]. This means that this new playback bit-rate feature is NOT quite a replacement for the bit-rate options in Quicktime (since Quicktime has not been required for a while).

Below is the Quicktime control panel showing the Sound Out bit rate control which is only available with Direct Sound. If choosing WASAPI, no bit rate control is available.

Which begs the question: without the Quicktime control, what default mode was iTunes using?

SWEET SPOT?

Having never supported WASAPI exclusive mode, iTunes will re-sample every track to the sample rate set by the player. Audio purists will immediately see this a not bit perfect. However, upsampling everything may not be a bad thing. Benchmark Media has been encouraging using iTunes upsampling for some time now [link]:

Sample rate can be set to match the sample rate of the media or to the highest that the audio interface is capable, since the upsampling in iTunes is harmless… The user should not be discouraged from setting the sample-rate to 96 kHz as a permanent setting, even when the audio is less then 96 kHz.

Further, the Sabre32-based DAC, seems to have a sweet spot with higher input sample rate. Thus the higher sampling rate seems to be specially beneficial to Sabre32-based DACs.

MORE LISTENING TESTS

I spent some more time comparing 11.0.2  iTunes playback at “bit-perfect”, in this case 44.1K material vs. upsampled to 192K/24

Even though I am not one that has the capability to detect minute differences (for example by changing a passive component such as a capacitor or a power supply), this time I was able to readily hear differences between the two playback sample rates. In all cases, I preferred the upsampled playback. This says that the differences are not minute.

The 192K/24 playback provided the following improvements:

• A more 3D soundstage. Some would say more “holographic”
• More detailed resolving of the sound.  The same sounds, but “finer”, more “delicate”, or some may say “super high resolution”.
• The harmonics gave a “greater presence” of the music. Perhaps greater dynamics.

EFFECT OF FILTERS?

I am sure there is no magic with the Apple upsampling algorithm, and there is no way to add information that in not there to start with. The only other explanation for the improvement is the use of different filters in the Sabre32 DAC.

MORE INFO

http://www.qobuz.com/info/MAGAZINE-ACTUALITES/HI-FI-PRATIQUE/iTunes-et-le-24-bits-a-192-kHz-oui173410