Whitepaper
www.denon.eu
WHITE PAPER
USB DAC GUIDE TO COMPUTER-AUDIO | 12.2015 | 3
AUDIO FORMATS AND TAGS
Let’s first make a quick review of the most used audio format.
For this we need just to step back to the original digital audio source on the
market, the CD. To get the analogue audio signal stored on a CD it needs to be
digitized and this is done with a technology called Pulse Code Modulation (PCM).
For the CD the PCM signal is fixed to a 44.1 kHz sample frequency and 16bit
resolution, so it is often referred to 44.1 kHz/16bit. Packed with a special algo-
rithm this information is stored on a CD. If you store it on a computer the format
will change to be compatible with the computer operation system.
On a PC, the equivalent of PCM from a CD gets the file extension. WAV (Waveform
Audio File Format WAVE/WAV). On a Mac this will be. AiFF (Audio Interchange
File Format).
However the files require a big memory space. Therefore formats have been
introduced to the markets which compress audio to reduce the memory space
required. Some are lossy (data reduced - lost) others just compress the file, but
keep the original quality – lossless formats.
Metadata - TAGs
Beside the need for large-size memory, there is another disadvan-tage of WAV
files. WAV can only carry very limited metadata’s (tags). However, tags are very
useful as these contain information about the artist, title, album, cover art, etc.,
in other words, every- thing that is needed to build up and maintain a music
library easily. The WAV format isn’t the best choice to do so. That’s why it isn’t so
often used even though the quality is like the original CD.
Other formats that do support tags are listed below and are preferred over WAV,
but we have to be careful because of the quality. Let’s start from the Lossy audio
compression formats that are used most, due to their small size and ease-to-
exchange on the web.
However as “lossy” already tells you, they don’t oer same quality as WAV.
MP3 is a data reduced (lossy) audio compression format that saves a lot of space
but also decreases the audio quality. It’s available in dierent compressions like
96kbs (kilobits per second), 128, 192 and 320 kbs. The higher the number, the
better the quality.
AAC the most used for iPod’s, iPhone’s and iTunes is also a compression format,
and also lossy format.
WMA is the Microsoft Windows Media Audio Format and it’s also a compressed
and lossy format. All are used because of lower data, less memory required and
faster transmission when downloading from the internet.
However, as memory size is no big issue anymore and internet speed is high,
there is no good argument left today to go for data reduced formats as shown
above. So let’s have a look at the below no-data- reduced formats and you will
recognize a trend to even exceed the quality level which a standard CD can
deliver, by new audio formats downloadable from the internet.
Here are the most common Lossless compression formats:
ALAC (Apple Lossless Audio Codec) 24bit/96kHz max (most used is 16 bit/44.1 kHz)
WMA Lossless (Windows Media Audio Lossless) 24bit/96kHz (most used is
16 bit/44.1kHz)
FLAC (Free Lossless Audio Codec), it’s an open source codec GNU GPL;
often used is 16 bit/ 44.1kHz, but 24bit/88,2kHz and 24bit/96kHz gained
a lot of popularity lately. And for high definition audio there is FLAC HD with
192kHz/24bit.
These 3 are lossless compression formats and also include the useful tag
functionalities.
All above are PCM – Pulse Code Modulation – Signals; however there is another
very interesting audiophile format called DSD.
DSD or Direct Stream Digital is a one bit recording format and is used on
SACD – the Super Audio CD oering much higher resolution than standard audio
CD. By that, it gained a reputation as an audiophile medium.
If you store the information of an SACD on you PC or download a file from the
Internet, you will find two file extensions: DSF and DFF. DSF has the ability to
hold metadata (TAG) and DFF doesn’t. Both can be played back on your computer
running a supporting media player. To transfer the digital audio signal via USB, a
technology will be used known as DoP – DSD over PCM. DoP is an open Stand-
ard Method for transferring DSD Audio over PCM Frames. On the DAC side the
signal will then be converted back from PCM to the original DSD stream without
any loss. It’s just a way of sending data in an already known standard. There are
dierent types of resolution available. These are 2.8MHz as used on SACD, but
as well 5.6MHz and 11.2MHz, so double and four times the resolution. Files will
be marked as DSD2.8 / DSD64, DSD5.6 / DSD128 or DSD11.2 / DSD256. The
64, 128 and 256 just mark the multiple of the standard CD sample frequency.
You remember?
Correct 44,1kHz. 64 x 44,1khz = 2.8MHz and 128 x 44,1kHz = 5.6MHz.