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View Full Version : configuring BEST digital audio out of an imac running itunes.




scott911
Sep 5, 2013, 09:41 AM
I have an imac, connected to a DAC (part of a stereo) via a optical cable.

Even though I have my audio files ripped at lossless ( managed in itunes) the sound quality is notifiable lower in quality that using a traditional CD player plugged into the same DAC.

I am not a regular MAC user, and need some assistance; I think there may be a dumped down audio setting that is lowering bit rate, etc. somewhere I can not find.

IN PC itunes,I noticed there is a preference setting in playback that lets you configure Bitrates for audio playback and Bits Per Sample For audio. The default on PC install was pretty poor.

So where is that setting on the MAC?



Julien
Sep 5, 2013, 11:28 AM
...Even though I have my audio files ripped at lossless ( managed in itunes) the sound quality is notifiable lower in quality that using a traditional CD player plugged into the same DAC.

I am not a regular MAC user, and need some assistance; I think there may be a dumped down audio setting that is lowering bit rate, etc. somewhere I can not find....
Most likely you have the output level turned down. In iTunes set level (see pic). Also you can open Applications: Utility: Audio MIDI Setup to see sampling rate and bit depth.


http://photos.imageevent.com/williamjulien/eastbayshirt/Screen%20Shot%202013-09-05%20at%2012.20.51%20PM.jpg

http://photos.imageevent.com/williamjulien/eastbayshirt/Screen%20Shot%202013-09-05%20at%2012.29.17%20PM.jpg

ChrisA
Sep 5, 2013, 11:43 AM
I have an imac, connected to a DAC (part of a stereo) via a optical cable.

Even though I have my audio files ripped at lossless ( managed in itunes) the sound quality is notifiable lower in quality that using a traditional CD player plugged into the same DAC.

I am not a regular MAC user, and need some assistance; I think there may be a dumped down audio setting that is lowering bit rate, etc. somewhere I can not find.

IN PC itunes,I noticed there is a preference setting in playback that lets you configure Bitrates for audio playback and Bits Per Sample For audio. The default on PC install was pretty poor.

So where is that setting on the MAC?

First off I bet you are talking about a "Mac" not a "MAC" they are different thing. A MAC is part of a networking device.

The settings for bit rate and bit depth is done with an app called "audio midi setup". Find it in the applactions folders. THis is also where to select the audio input and output devices in you have several of them.

Last question is how you measured audio quality? Are you sure the difference is real and do you have any numbers? The source material (CD) is at 44.1K and 16 bits. Moving the system audio setting to 96K and 24 bits will not change the source material. Up-sampling can't help.

One difference between PC and Mac audio is that Windows has a longer and more complex audio system. The bits get processed. Many musicians replace the Windows buillt-in audio with ASIO drivers. these provide the same kind of direct path found in Mac OS X and bypass Windows' many layers of processing. That said, you may just happen to LIKE the processing and this is the difference you are hearing. Try ASIO and see Audio_Stream_Input/Output (http://en.wikipedia.org/wiki/Audio_Stream_Input/Output)

The Mac just dumps the bits out pretty much as they are stored (like ASIO). However this assumes all you digital volume setting are at 100%

That last part is important. Any setting other than 100% kills dynamic range and in effect lowers the bit depth. There are two volume settings, one in iTunes and also the system volume. Set them both to full up.

One other experiment. Remove the stand alone DAC from the Mac and play the audio output directly. Depending on the model you have the built-in DAC inside the Mac might be better then what ever you are using. At least this will remove on layer of processing and mmake the system closer to just playing a CD.

scott911
Sep 5, 2013, 12:40 PM
Perfect - both you guys are awesome - thanks for the solutions.
I will try them soon.

Note that the DAC is a emotiva unit, and I'm driving Thiel 2.4 se speakers.
The difference I'm hearing is a comparison between a source CD transport, and the Mac's digital output, both with same signal path starting with the DAC.

Ultimately, the DAC just wants the ones and zeros, so I'm thinking your comments are all right on target with what I need to do to restore the dynamic range on the mac as a source.

Julien
Sep 5, 2013, 03:10 PM
Perfect - both you guys are awesome - thanks for the solutions.
I will try them soon.

Note that the DAC is a emotiva unit, and I'm driving Thiel 2.4 se speakers.
The difference I'm hearing is a comparison between a source CD transport, and the Mac's digital output, both with same signal path starting with the DAC.

Ultimately, the DAC just wants the ones and zeros, so I'm thinking your comments are all right on target with what I need to do to restore the dynamic range on the mac as a source.

Just a quick point. The audio levels of must be matched within 1dB to make any meaningful SQ comparison. Even the most golden ear's become unable to judge quality if the levels are mismatched by just a couple of dB. The louder signal will almost always sound better at first (hence loudness wars in recording). Also DBT is recommended but complex and involved to truly determine if one signal is superior.

ChrisA
Sep 6, 2013, 12:00 AM
Just a quick point. The audio levels of must be matched within 1dB to make any meaningful SQ comparison. Even the most golden ear's become unable to judge quality if the levels are mismatched by just a couple of dB. The louder signal will almost always sound better at first (hence loudness wars in recording). Also DBT is recommended but complex and involved to truly determine if one signal is superior.

Yes, that is right, you have to MEASURE the volume levels. You can buy a sound level meter from Radio shack that is good enough for this. Or if you are setup with a microphone for recording and have a software meter. As said above you can't hear 1dB. You have to measure. The meter is good and will help you measure speaker sensitivity and freq. response too