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  November 1 st , 2004


The project was born from the idea to always have all my software (music) with me in any place. Obviously who knows to me will never imagine that I am talking about a portable MP3  player because I want the same sound quality as the original CD.

A test done with the EAC free software (Exact Audio Copy from )  demostrated  that the PCM files (.wav) extracted with this audio grabber could be better than original.

Given that situation, I decided to have a look in the portable PC market for the storage solutions.
The current 2.5" technology for portable hard disks with USB 2.0 or Fireware interfaces is available on the market up to a capacity of 80GB with a reasonible price. These disks are smaller than their 3.5" mates, with a noticeable plus: no need for a separate power supply, because they get energy from the USB connector.
Wiithin a 80GB disk we can suppose to store a max of (80GB /  600MB)  133 CD. Such an amount is not enough for the 'normal' audiophile, at least it is not enough for me! In my opinion a significant amount of CDs is around 500 (BTW, strange but many people involved in audio diy, or even interested in hi-fi / hi-end equipment will spen alot of money in electronics, and not so much in music CDs ..)

In order to store more CDs I searched the Internet for a lossless audio compressor, geting a relevant result:
TTA (True Audio Software  from )

Here the main feature description from the TTA website:

'TTA codec performs lossless compression on multichannel 8,16 and 24 bit data of the Wav audio files. Being "lossless" means that no data/quality is lost in the compression - when uncompressed, the data will be identical to the original. The compression ratios of TTA codec depend on the type of music file being compressed, but the compression size will generally range between 30% - 70% of the original. '

Not bad,  at this point I decided to perform a quick test to check if I can 'rebuild' the original PCM file (.wav) with such a procedure:

As you can see the original PCM file and the double-processed one show the same MD5 fingerprint:

02/10/2004  10.04    <DIR>          .
02/10/2004  10.04    <DIR>          ..
15/04/2003  22.09            49.152 md5.exe
02/10/2004  10.01        32.626.138 test_local_compressed.tta
02/10/2004  10.04        54.684.044 test_local_compressed.wav
02/10/2004  09.57        54.684.044 test_local_noncompress.wav
12/05/2004  11.09            73.728 ttaenc.exe

C:\audio>md5  test_local_compressed.wav
FFF5687368BB6F6FD7F4E81ABACB2C3C  test_local_compressed.wav
C:\audio>md5  test_local_noncompress.wav
FFF5687368BB6F6FD7F4E81ABACB2C3C  test_local_noncompress.wav

The encoder is very easy to use because you need only to start in the Windows command line the program ttaenc.exe with the following syntax:

ttaenc -e [input file] -o [output file]

To open the Windows command line follows these simple pictures.

Select Run in the main menu and type cmd or command in the Run window.
The cd command following by the directory name will be use to enter the target directory of your disk.

In order to speedup the process of storing all the TTA compressed files in the hard drive, it is possible to integrate the TTA encoding in the EAC software with the following setup:

Setting these option the EAC software will automatically compress any extracted file with the TTA encoder, leaving in the target directory just the compressed files.

With this solution is resolved any problem of reading errrors and degrade of quality of the CD.

Offcourse the sound quality of normal PC audio interface is low and we want a true Hi-End quality.

Exploring the commercial products of the external audio interfaces I have found and tested all these choices:


From the M-Audio website:

Audiophile USB is a compact audio and MIDI interface that builds on the success of our popular Audiophile 2496—awarded Best Soundcard by Computer Music magazine. AC-powered components allow Audiophile USB to deliver some of the best fidelity, frequency response, dynamic range and noise specs available in a USB interface. You also get digital I/O for pristine transfers, as well as the ability to pass AC-3 and DTS surround sound signals. MIDI I/O rounds out a great compact interface that’s easy to take anywhere you want to take your music.

This interface give this features:
The external power supply should promise an higher sound dynamic than bus-powered circuitry

The hardware is based on the AK4528 Codec with high performance 24bit 96KHz, dynamic range.
The datasheet is available on the Asahi Kasei Microsystems website


From the M-Audio website:

Small enough to fit in your pocket, Transit brings hi-resolution 24-bit/96kHz recording and playback to any USB-compatible computer. Digital I/O lets you transfer pristine audio between your computer and other devices such as MiniDisc and DAT. The digital output can deliver AC-3 and DTS from your computer to an external decoder such as a surround receiver. And the bus-powered design allows you play and record virtually anywhere your laptop can go. Transit is your ticket to ride.

This interface give these features:

The hardware is based on the AK4584 Codec with high performance 24bit 96KHz DAC with dynamic range.
The datasheet is available on the Asahi Kasei Microsystems website


From the Audiotrak website:

OPTOPlay is the unique, yet simplistic USB device for high quality analog and digital output. Simply plug OPTOPlay into your PCI's USB port and instantly listen to 24-bit 96kHz professional quality audio.

OPTOPlay brings you to the amazing world of Dolby Headphone Technology, a unique signal-processing system that enables your stereo headphones to portray the sound of a five-speaker, surround-sound playback system. With Dolby Headphone Technology, sounds that were designed to come from all around you are actually heard that way and not out of each side of the headphone.

OPTOPlay's compact design and high-fidelity headphone amp delivers the ultimate portable audio solution with professional

This interface have these features:

The hardware is based on the AK4353 DAC with high performance 24bit 96KHz DAC with dynamic range.
The datasheet is available on the Asahi Kasei Microsystems website

The output stage use the MS6308 by MOSA ELECTRONICS CORP ( a Class AB Stereo Headphone Driver compatible with the Philips, TDA1308T.

I have found on the Head-Fi forum ( an easy modification about this interface by doobooloo user to skip the output stage and get the signal directly from the DAC chip (click to enlarge).


This upgrade is a sure step to increase the sound quality but after this modification is no more possible use the Optoplay to drive directly headphone.

Follows a comparation table:

Audiophile USB
DAC chip
AK4528 Codec
AK4584 Codec
AK4353 DAC
24 bit 24 bit 24 bit
24 bit
sampling speed
96 KHz 96 KHz 96 KHz 96 KHz
DAC dynamic range 104 dB 98 dB 96 dB 116 dB
DAC S/N 104 dB 98 dB 96 dB 116 db
DAC load resistance
1 kohm
5 Kohm
10 Kohm
1 Kohm
DAC load capacitance
25 pF
25 pF
25 pF

DAC out voltage
5 Vpp
3 Vpp
3 Vpp
4.8 Vpp
Output stage
low noise operatinal amplifier
low voltage operational amplifier
class AB headphone amplifier

Output chip 5532

47 ohm

>= 600 ohm
>= 600 ohm
>= 32 ohm

The DAC included in these products have not the same specifications of the last generation reference chips like AK4393. AK4394, AK4395 or AK4396 but in any case the quality is very  good.
To drive my headphone Beyerdynamic DT 880 with an impedance of 300ohm the best since to be the Optoplay probably because is the unique with a true headphone amplifier.
But the Audiophile USB is the unique with enogth output voltage to drive the my headphone.
The my idea is to use the Optoplay or the Transit excluding the output stage and build a true hi-end tube amplifier.


The car solution to play the TTA files stored in the my portable hard disk is a PC with serial LCD display and simple keyboard.

I have develop a software in Visual C++ to navigate in the directory of the PC with only few key (4 are necessary) and display the status in a serial LCD display (4 rows x 20 columns).

The first selection is the harddisk,
the second the directory and after
the album. An arrow indicate the
current position.
  • key 2 to go up
  • key 8 to go down
  • key 5 to enter in the direcoty or play
  • key 4 to go one level back
To debug the code I have implemented in the software also a simple interface windows.

You can use any VIA Mini ITX motherboard to create a car PC with any type of Windows version or you could use my solution:

The Vortex86-6082 used is a very little board with a size of only 100 x 66 mm including all the functions of a normal PC: vga,  usb, serial, mouse and keyboard ports, IDE controller and 128Mbyte of RAM.
Offcourse the cpu clock (166MHz) is a little low if compared to new generation pc but for this use is enougth.
Tha my first idea was use a Linux with a opimized kernel but I have found some problems using my USB Audio device.
With both the
sound architecture: ALSA and OPENSOUND there was some strange interruption of music also if the cpu load was load (about 30%) and also using high nice or realtime kernal patches and set.

The 2.5" 80GB hard disk has been connected to the ide port with a simple 44 pins flat cable to create a very compat object.
Leaving linux the alternative on low perrfomances boards is the Windows CE and  the new Winows XP Embedded.
Windows CE is best choice in this cases but have no USb audio support so Windows XP Embedded has been the choice.

from MIcrosoft website:

Windows XP Embedded is a componentized version of Windows XP Professional that contains all of the features, functionality, and familiarity of Windows XP Professional. Windows XP Embedded enables you to rapidly develop reliable and full-featured connected devices. By supporting standard hardware and software, Windows XP Embedded makes it easier and less expensive for you to build a run-time image.