Wiresman's Blog

bit-perfect doesn’t mean a thing

wiresman — Sat, 14 May 2011 09:32:38 +0000

With perfectionist audio, a perfect digital chain is ofter described as “bit-perfect”. When two player applications are both bit-perfect; there should be no audible difference between them (when the rest of the chain remains unchanged of course). People now realize this is wrong; they hear differences between players such as Amarra, Decibel and Itunes. Actually this observation is not heavily discussed; most people can hear it. So clearly bit-perfect alone is not enough to describe the quality of a digital audio player. When describing a DAC; bit-perfect is not a point of discussion, however another parameter called ‘jitter’ is (check wiki for background on jitter). Jitter is the equivalent of hum and noise, but now in the frequency domain. Minimizing jitter requires perfect (relative) timing. Actually timing is key in any digital audio environment. Actually timing is key in any music produced; music consists not only of a series of notes; each note has to sound at the right moment in time.

So we have not only ‘bit-perfect’ but also ‘perfect-timing’ as parameters describing a digital audio chain. These parameters apply to audio software (player and OS) as well as audio hardware (cabling and DAC). May it be jitter that makes Amarra sound better than Decibel? Can the logic in the player and OS software influence the timing of the digital audio data stream? Well, in order to explain the audible differences it has to be…

A common issue with Itunes is it’s build-in sample rate converter. Why it’s there is easily explained; it needs to be there because Itunes can drive an Airport Express. An AE relies for it’s timing (clocking) on Itunes; Itunes is the master clock driving the AE. Your DAC/OS-driver also has a build-in clock; normally this clock would ‘clock’ the audio player. But with Itunes being master clock (for AE) we then have two masters… And that’s why Itunes needs sample rate conversion build-in. Any sample rate conversion has impact on timing; and there we are: Itunes sounds worse than programs like Amarra or Decibel because these players can slave to the DAC/OS-driver clock. Itunes can still be bit-perfect; but without perfect-timing this means nothing.

The differences between players like Amarra and Decibel are much more subtile. Maybe it’s the way their interfacing to the OS driver is programmed? But it’s must have something to do with timing, that’s for sure. With closed player software it’s difficult to determine the differences; although DAC hardware is mostly ‘closed’ as well. Why not perform (relative) jitter measurements on software players? Same DAC, OS, Soundfile etc. but different player software? Anybody?

Wiresman on Mac.

Transferring mail from Outlook to Mac

wiresman — Fri, 05 Feb 2010 14:37:18 +0000

A lot is written about this. I’ve found that it can be extremely simple. This is how to transfer your emails, including attachments and your folder structure from Outlook on your PC to Mail on your Mac.

On the PC install Mozilla Thunderbird 3.0, don’t worry it’s free. During Thunderbird setup, choose to import your Outlook mail. When done, close Thunderbird; there’s no need to configure an email account. Next step is to find the folder where your mails are stored on the PC. This might be a little difficult…

The following works on WinXP, Vista and Windows 7 will work along the same line. First enable ‘view hidden folders’. It’s in your explorer’s menu “Extra -> Folder options, tab Display. Then goto C:\Documents and Settings\USERNAME\Local Settings\Application Data\Thunderbird. There you find some “dasgfsdf” folder; i.e. a random folder name. This folder is your Thunderbird profile folder that holds your emails. Transfer this folder to your Mac in some way (USB-stick, USB-disk etc.). The trick is that Apple Mail can import Thunderbird mail by searching for mail files in a folder. So; start Mail on your Mac and select import; Thunderbird mail. Navigate to your profile folder and let it search…

All your outlook folders will be imported and shown below “Import” in the left pane of Mail. You can now drag’drop everything ”one level up” and you’re done. Enjoy full text search on all your emails with spotlight. By the way, you do have Time Machine enabled don’t you?

The basis for these types of data & platform migrations is to find an application that is available on both platforms and supports import/export. In case of email; Thunderbird will rescue you. Note that on the Mac, email is stored in the mbox mail format. One mbox file represents one mail folder and can contain multiple emails. Mbox files are plain text files; wanna know what route your email took or how it’s classified by your provider’s spam filter? Just open the mbox file with any text editor and check it out. Why not give “vi” a go from a terminal window?

Wiresman on Mac.

Remote printing from PC to Mac

wiresman — Fri, 22 Jan 2010 13:46:52 +0000

At our home we have a number of PC’s and just one printer. Two weeks ago I finally replaced our ‘main’ PC with a Mac; a Mac Mini. Being a Unix man since I could read and type 2 letter commands on a terminal this feels great. At last a real desktop system running Unix… Do you have a problem with sharing iTunes music across multiple users?? Just ‘chmod’ the offending directory properly and off you go…

Now back to this printer I’ve got. It’s a HP C3180 and directly connected to the Mac Mini. OSX 10.6 installed the proper driver automagically and all works out of the box, both printing and scanning. No bloatware (buy HP cartridges online..) but just the basics such as displaying the ink levels for the black and color cartridges.

So far so good, now the PC users at home want to print on this C3180. Of course I won’t allow them to have a login on the Mini and carry documents on USB-sticks, that is so 2009… Therefor I need remote printing.

Traditionally Unix supports remote printing with LPR/LPD (BDS style) and LP (SysV style). And guess what, OSX support LPR/LPD style printing in a modern way, it’s called CUPS. Wanna try: type “http://localhost:631/” into your browser on your Mac. Presto; you’re connected to the printing engine. Check out wiki for CUPS and IPP for more info.

Bonjour is another nice piece of software from Apple. Bonjour makes all kinds of communication on your lan a breeze and guess what, it’s available for windows too. Wanna remote print from PC to Mac? First install bonjour for Windows (1.0.6 is the latest) on all your PC’s. This creates a remote printer wizard icon on your desktop. This is what we’re gonna use, but first I’ll explain this remote printing interface on your Mac a little more.

CUPS implements a print queue that holds all your print jobs. In order for different users and PC’s to print to this single queue, it would be nice to use a common format for each print job. Well, this common format is actually a world standard and it’s called postscript. (real printers talk postscript..) My C3180 printer is a cheap and dumb printer; it does not know postscript. Here the printer-driver comes into play. Postscript jobs from the queue are processed by the printer-driver into the proper format for my C3180. So actually CUPS transforms my Mac/Printer combo into a postscript printing system (isn’t that cool).

What does all of this has to do with remote printing and bonjour you might ask. Well anybody who has run the bonjour remote printing wizard on windows already knows… Run the wizard and check if it finds your Mac/printer combo (make sure printer sharing on your Mac is switched on). Next select generic/postscript als your printer type; this is key to make this work. This will install an Apple Color Laser Printer (being a postscript printer that windows knows about) on your windows PC. Check out the printer queue on your PC and you’re actually looking at the queue on you Mac! Try this: switch off your printer and print something on your Mac; this will leave a job in the queue. Then check the print queue on your PC… So now you can print from PC to Mac, actually from all your PC’s to Mac since the Mac/printer combo is acting as a networked postscript print server.

How about printing to a printer that’s connected to an Airport Express? Do you think this tiny white box implements postscript and a queue? Ehhh, no. There’s no CUPS on the AE and therefore each Mac or PC that want’s to print to an AE has to install a printer-specific driver. The AE implements a so called raw interface to your printer (on TCP port 9100). As a result you have to select a printer-specific driver when running the bonjour for windows printer setup wizard. I’ve not yet tried this; so I don’t know if you can select your specific printer in this case. Otherwise select “have disk” and navigate to the proper directory where your printer driver setup file (*.inf) is located .

Finally one nice trick (Unix rules!) on how to remove incorrect print jobs from the queue. These jobs might occur during testing, for instance when you select Generic/PCL instead of generic/Postscript in the bonjour setup wizard. On your Mac, open a terminal window and type “cancel -a”. This will cancel all (-a) print jobs in the queue of the CUPS printing subsystem. Check it out with “man cancel”.

Wiresman on Mac.