iTunes and 192khz.

[RankStranger]

Sorry if this is already covered in one or another topic but I have the flu and can't muster the energy to search through all the forums.

 

What happens if I put a 192khz res file into iTunes? will it recognise it? will it play it? will it downsample or downsize it in some way? I ask because I'm looking at getting some and iTunes is my only playback software so I don't know if it's worth it. I seem to recall that itunes only supports up to 96khz.

 

Cheers,

 

RS

 

[Akapod]

iTunes can play 192 kHZ. Be sure to adjust Audio MIDI Setup appropriately.

 

[RankStranger]

ok, I checked audio midi setup and it only goes up to 96khz. is that an issue?

 

RS

 

[gcorley]

Which output are you using? The built-in optical out only goes up to 96.

 

 

 

[RankStranger]

so it will only give me the 192 option if I have it connected to a DAC which will decode 192? and that would have to be via some sort of halide bridge-type interface?

 

So what happens if you're using the built in optical out? will it downsample? if so, will it do it well?

 

RS

 

[Akapod]

The new Ayre QB-9 handles 192 kHz. And Firewire-based DACs, like Apogee's Ensemble, can handle 192 as well.

 

If you elect to use the optical out, iTunes will automatically downsample to 96 kHz. This is an easy calculation to perform, as all iTunes has to do is ignore every other piece of information. (Upsampling is another issue.)

 

[Miska]

This is an easy calculation to perform, as all iTunes has to do is ignore every other piece of information. (Upsampling is another issue.)

 

No, it's not that easy. You would just get severe aliasing.

 

Downsampling and upsampling (ie. resampling) are pretty much equivalent operations.

 

 

[Akapod]

Miska -- can you give us some more information on the aliasing problem? And wouldn't the aliasing apply to only frequencies above 48 kHz?

 

[Miska]

can you give us some more information on the aliasing problem? And wouldn't the aliasing apply to only frequencies above 48 kHz?

 

When you half the sampling rate from 192 -> 96, any frequency content between 48 kHz and 96 kHz before discarding samples will be folded down between 0 Hz and 48 kHz in the new rate.

 

Since that HF content will be at full level and likely is not even random noise, it will reduce SNR and most likely also sound quite bad since it's correlated noise.

 

[Akapod]

Aah. Interesting.

 

So could you correct the problem by inserting a lowpass filter at 20 kHz before the downsampling?

 

And though my description of the process was wrong, it appears from other discussions on this site that CoreAudio (not actually iTunes) does a good job of downsampling -- is that fair?

 

[Codifus]

......and the low pass filter would be set to 48 Khz, the nyquist frequency for 96 Khz audio.

 

CD

 

[Miska]

Yes, lowpass filtering is needed around Nyquist frequency. And the design detail specifics of that lowpass filter has quite significant impact on sound quality.

 

CoreAudio is on the better side of average regarding quality.

 

[Daudio]

I don't see anything like that on my Mac OS 10.4.

 

I have a 'Sound' preference pane, and an 'M-tech Delta' Control Panel for my Audiophile-192 card, but no 'Audio MIDI' that I can find...

 

Inquiring minds want to know

 

[goldsdad]

Hi Daudio,

Try in the Utilities folder inside the Applications folder.

 

 

[Daudio]

what should I do with it now ?

 

I thought I had adequate control with the M-tech Delta control panel (through it has a terrible interface). Is there more to do with the 'Audio-MIDI' tool ?

 

Thanks,

 

[Codifus]

1. Set it and forget mode is where you set audio midi to the highest sample rate that your DAC can accept. For example if your dac can accept 192/24, set audio midi to that setting. Now, after you relaunch iTunes, it will play 192K files bit perfectly and upsample any lower rez audio, such as 44.1K or 96K, to 192K before passing it onto CoreAudio and onto your DAC. The iTunes upsampling algorythm has been tested by Benchmark Media, makers of the famous DAC1, and they found it to be very good so many users should be happy with this setup;

 

http://www.benchmarkmedia.com/wiki/index.php/ITunes-QuickTime_for_Mac_-_Setup_Guide

 

 

 

 

2. Set Audio midi to the sample rate of the files you will play. You set audio midi to your chosen sample rate , say 44.1 Kz. After you relaunch iTunes, it will play 44.1K files bit perfectly and downsample any higher rez audio, such as 192K or 96K, to 44.1K before passing it onto CoreAudio and onto your DAC.

 

If you wan to play every audio file bit perfectly, you would repeat step 2 every time you changed the type of audio file you are playing.

 

You can now see why everyone wants iTunes to incorporate automatic sample rate switching that programs like Ammara and PureMusic have.

 

Hope this helps.

 

CD

 

[Akapod]

(Apologies -- this should have been placed in a different topic).