New iMac with OSX 10.5.2 and iTunes - Thoughts?

[hifimaker]

Paul, Really nice tutorial on the Benchmark site.

I also checked out Gordon's site. He has great information there as well.

http://www.WavelengthAudio.com/

-David

[-ecdesigns-]

Just discovered that Benchmark Media have a wiki page on setting up OSX for bit perfect playback:

I get MUCH better sound quality from the mini-TOSLINK output of my Apple airport express module when using iTunes 7 (44.1/16 recordings). I performed a direct comparison with the TOSLINK output of my CD reference player. I use a highly effective jitter blocking system so I am pretty sure jitter isn't causing this.

Since these TOSLINK outputs are bit-perfect (verified), the iMac mini-TOSLINK obviously isn't, same applies for USB audio. I double and triple checked all settings in iTunes, MIDI, quicktime VLC, and so on. Volume control was always set to maximum, sound enhancers all disabled. I also followed the setup guide to see if I missed something.

I think bit-perfect playback is VERY important for High-End audio. Non bit-perfect playback usually means that ALL original sample values are changed (averaged), so I am not talking about a few samples that have a different value. The effect on the audio signal is reduced sound stage (flatter sound), loss of resolution and transparency.

So at the moment I am only able to get bit-perfect playback from my iMac using an external airport express module.


The only major difference between iTunes 6 and iTunes 7 is the integrated SRC and 24 bit connection to Core audio.

When using the airport express module, iTunes volume control can be disabled (disable volume control for remote speakers), the volume slide in iTunes is now fixed and cannot be changed. iTunes then sends the digital audio file (probably Apple lossless format) to the airport express module buffer memory over a (wireless) computer network. Dedicated hardware (Broadcom BCM5231 & TI PCM2705) in the airport express module is then used to convert the audio file to a SPDIF signal.

[sek]

Hi there,

Originally posted by jonnywolfet
one thing you should be aware of in itunes is that the encoders are not quite as good as LAME or equivalent.

If, for whatever reason, MP3 is required, LAME can be fit into iTunes to replace the original QuickTime algorithm.

But there is no reason, as there already is MP4 in it's incarnation as Advanced Audio Codec (AAC) as per the default encoder settings. Less space for the same quality, more quality in the same space, or both.

Other than that, why compress lossy at all? 320GB is plenty and additional space later on will be cheap! If in doubt, use Apple Lossless, it's Apple's implementation of the FLAC idea.

Originally posted by dw8083
The sound is much more relaxed ripping WAV files from CD's with iTunes than the same files from EAC on Windows. iTunes does have the Error correction option checked.

Interresting description, although the result with EAC should be more accurate. iTunes supports error correction in the drive, which relies on the drive's capability to detect errors in the first place. iTunes, otoh, doesn't use sophisticated statistic analysis of the disk in order to regain even the uncertain bits. It checks for weak bits, but goes to less extreme efforts in order to recoup them.

I myself use EAC and iTunes. On the same Mac.

Originally posted by Wavelength
You might want to rip to AIFF. WAV is basically straight PCM data. But AIFF from what I can tell is straight PCM data with a wrapper around it that has the CUE information. Therefore if you loose your library info with WAV your screwed but with AIFF it can rebuild everything very easily.

Not quite. The library information is way more than you might think. The track titles and such are just the bare minimum (think playlists, usage statistics, smart playlists, store account, ipod connections, etc.). The technique described above does not prevent data loss!

AIFF is Apple's Audio Interchange File Format, a format to interchange between computers and platforms over unknown media. These properties and their versatility are not required in a media archive.

First of all, I recommend a backup in order for having a backup.
Time Machine comes in very handy here!
And second of all, if you use Apple Lossless (or any other codec except WAV), the described problem is nonexistent.

Originally posted by -ecdesigns-
Since these TOSLINK outputs are bit-perfect (verified), the iMac mini-TOSLINK obviously isn't, same applies for USB audio.

The explanation for this observation is simple: iMac audio actually is USB audio. And USB is known for it's timing deficiencies in streaming applications.

iTunes then sends the digital audio file (probably Apple lossless format) to the airport express module buffer memory over a (wireless) computer network. Dedicated hardware (Broadcom BCM5231 & TI PCM2705) in the airport express module is then used to convert the audio file

The current generation Airport Express modules use a different chipset (providing 802.11n capability), but the same principle applies.

Airtunes uses Apple Lossless via wireless lan, which is another good reason to encode in Apple Lossless, as it saves a transcoding step (and thus computing power, energy, etc.).

There are a lot of unknown or uncertain things about Airport Express (and it's Airtunes) among it's potential users. Did you know that you can use multiple Airport Express modules in order to simultaneously stream lossless digital audio to speakers in the same room, with Airtunes taking care of buffering the sound with as little latency as required for playing back the sound sample-aligned via a smart timing protocol? Sounds unneccessary? Think wireless lan capable active speakers, providing managed signal routing and centralized configuration. All you need is a wall outlet nearby each channel. Not convinced? Think wireless listening room, production studio, home theater, etc. Still not convinced? Think spatial installation, mobile sound reinforcement, stage monitoring, etc.

[jaycee]

Originally posted by sek
The explanation for this observation is simple: iMac audio actually is USB audio. And USB is known for it's timing deficiencies in streaming applications.

Wrong - iMac audio is the new UAA HD Audio architecture using a Realtek ALC 885 codec.

When I connected a friends Zhaolu DAC to my iMac, the system volume control was disabled, however iTunes has it's own control which does scaling, and thus loss of bit precision.

You might also want to check the preferences - Sound Enhancer is on by default, which is not what you want if you want to listen to your sound as stored.

[sek]

Originally posted by jaycee
Wrong - iMac audio is the new UAA HD Audio architecture using a Realtek ALC 885 codec.

Only partially right.

I was more speaking of iMacs in general. Apple has changed the audio controllers to the universal audio architecture in recent models, which is what applies to the original poster's iMac.

But the comment I was replying to refers to a post by ecdesigns who didn't state which model is in use.

When I connected a friends Zhaolu DAC to my iMac, the system volume control was disabled, however iTunes has it's own control which does scaling, and thus loss of bit precision.

This is difficult to comment on, as you are refer to a general pitfall of digital audio in general. No volume control in the digital domain can go without scaling - per definition.

This is neither the Mac's, nor iTunes' fault. Just keep the volume control at 100% and use analog volume control after the DAC.

You might also want to check the preferences - Sound Enhancer is on by default, which is not what you want if you want to listen to your sound as stored.

Sound enhancer is on by default for the built in output, i.e. built in speakers and headphone socket. But while the enhancement makes sense for the built in speakers, you can select an individual setting for each additional sound device. I recommend to leave it on for the built in speakers and check that it's turned off when using anything other than a set of multimedia speakers on the external output.

[Wavelength]

Originally posted by -ecdesigns-


I get MUCH better sound quality from the mini-TOSLINK output of my Apple airport express module when using iTunes 7 (44.1/16 recordings). I performed a direct comparison with the TOSLINK output of my CD reference player. I use a highly effective jitter blocking system so I am pretty sure jitter isn't causing this.

Since these TOSLINK outputs are bit-perfect (verified), the iMac mini-TOSLINK obviously isn't, same applies for USB audio. I double and triple checked all settings in iTunes, MIDI, quicktime VLC, and so on. Volume control was always set to maximum, sound enhancers all disabled. I also followed the setup guide to see if I missed something.

Guys,

Actually the Airport Express uses the PCM270x controller which is a USB DAC with digital output. The basic architecture of the Airport Express is this:

Airport/Ethernet<---->ARM7<---> Dual Host USB Controller: Pone-Printer USB, Ptwo ===>PCM270x analog and digital output.

Allot of diy users use this chip and it's ok. The newer N versions as well as all the newer MAC's and some iPod's are using Realtek dacs. People are not taking to the Realtek like Apple anticipated. They much more prefer the Wolfson which is still used in the iPhone and iTouch.

Most of the iMac's, Mini and MacBooks used the SigmaTel Codec with digital input/output. My new supped up MacBook (2.4GHZ, Samsung SSD 64GB, 4GB memory) seems to have the Realtek in it.

In my testing with the Prism dScope III the Airport Express did not fare as well as desktops or laptops digital outputs. I have several Core Duo, Core 2 Duo, G4 and G5 units here.

I have not checked out the new N version of the AE.

In most cases the use of Toslink can be considered marginal at best. While the newer transmitters and receivers are much better than a decade ago in most cases it pails in comparison to transformer coupled BNC SPDIF.

~~~~~~~

iTunes when the vol control is set a maximum does not do ANY calculation and therefore is bit perfect.

Some players always do the calculation some do the same thing as iTunes.

There is a mystery which I want to uncover in the PC area in that all the players I have sound different. I want to think it maybe a result of there not being specific libraries for all the media formats (i.e. Flac, WMA, etc...).

~~~~~~~

Just somethings about Adaptive USB as compared to SPDIF. First everyone thinks that Adaptive is really bad because the PC clock has to be matched to the USB controller and therefore changing the speed of the USB device to match the PC causes jitter. First that is no different than what happens on a SPDIF setup.

BUT... if you use a smart controller you can use the Adaptive setup in your favor and slowly move the clock much slower than you do with SPDIF.

Also there is Async USB mode which all my stuff uses. In this the data becomes merly that. A local clock is fixed and therefore can be really low jitter. Then the flow control between the Computer and the dac assures there is significant data so the dac does not over or under run. This results in the better Audio as compared to even slaving SPDIF transports and dac combo's.

Thanks
Gordon