Computer Audiophile FAQ
I'm a total beginner I don't even know what I don't know, where do I start?
What are the bare necessities or minimum requirements to use a music server with my audio system?
1. A computer running nearly any operating system.
2. A connection between the computer and the audio system. This can be USB, S/PDIF (optical TosLink or electrical coaxial), AES/EBU, FireWire, HDMI, Ethernet, or wireless. The computer's output ports and the audio system's inputs dictate what type of connection is needed. All Macintosh computers built today have an S/PDIF optical output port hidden inside the headphone jack. Some PCs offer S/PDIF output as well. Nearly all computers have USB ports but not all audio systems have an available USB input. Analog output is also an option. Running a 3.5mm mini to RCA cable from the computer's headphone jack to a preamp or receiver's AUX input is not recommended but does work.
What's better for a music server Apple OS X or Microsoft Windows?
Neither of the two most popular operating systems is better than the other when it comes to music servers. There are major differences between the two platforms. Both are completely capable of producing audiophile sound quality. The most important factor when determining what operating system to use for a music server is the end user's level of comfortability with the operating system.
What is an audio codec?
An audio codec is simply an algorithm or program that COmpresses/DECompresses audio data. Codecs can be lossless or lossy. Each codec has its own method of compression and decompression. Thus the audio quality varies greatly from codec to codec.
What is metadata?
In general metadata is data about data. In the context of audio metadata is information describing an album, artist, track, etc... There are major differences in how metadata support is implemented in audio applications. The most important difference is between associated metadata and embedded metadata.
This metadata is frequently stored in a proprietary database or file used by playback applications. When looking at an album within the application users will see all the information available such as album art, artists, track title etc... For example, when iTunes automatically finds album art it only associates this art with each track of the album. The problem with associated metadata is its lack of transportability. This metadata will only be available when using the specific application that associated the metadata with the files. If an iTunes library file is lost or an application's database of associated metadata is lost or if a file with associated metadata is moved to another application all the metadata is gone for good.
This metadata is stored as chunks inside the the audio file's container such as AIFF or FLAC. Containers / file formats such as FLAC, AIFF, M4A (ALAC) support embedded metadata that is readable and writable by many audio playback applications. These containers/file formats have guidelines or standards for embedding metadata and they allocate space within the container for this data. Once this metadata has been embedded into a container/file like AIFF the metadata is there until removed. None of the three problems described above are an issue with embedded metadata. Loss of an iTunes library file or proprietary application database or moving a file to another application have no effect on the metadata. Looking at a file with embedded metadata in iTunes will display album art, artist, track title etc... without manually entering anything or without iTunes gathering the metadata from an Internet database.
What's the difference between WAV, AIFF, AIF, MP3, FLAC, WMA, ALAC, M4A etc ...?
First a little background information. 99% of music played on our computers is formatted as PCM (Pulse Code Modulation) audio data or sometimes as LPCM (Linear Pulse Code Modulation). LPCM is PCM with linear quantization. PCM and LPCM will be used synonymously in this description. PCM is a digital representation of an analog signal. Very few music playback applications support playback of raw PCM data. Playing raw PCM data may seem like a great idea to audiophiles but in reality it's less than ideal. Raw PCM data contains only the digital representation of an analog signal. No album art or metadata like artist, album or track information and no information providing instructions to the playback application. In an effort to support file interoperability between many applications created by many companies file Containers / wrappers were developed decades ago. A container simply describes the enclosed data to the application opening the file.
Think of a container as a CD or DVD case. The case describes what's inside. It should contain a logo stating the enclosed material meets the Compact Disc, SACD, Dual Disc, or DVD-Audio standard. Liner notes inside the case frequently describe even more about the specific music contained in the case. The disc itself contains the actual music.
Container / wrapper = CD or DVD case
Metadata = Liner notes
Music data = Music on disc
Over the years many audio specific containers have been developed. These containers are frequently, and correctly, referred to as file formats such as AIFF, WAV, FLAC, and MP3. Each container or file format typically holds one of three types audio data. The three types are uncompressed, lossless compressed, and lossy compressed.
Uncompressed PCM audio is stored as a one for one copy of the original. Popular containers for uncompressed PCM audio are AIFF and WAV. Most people refer to AIFF and WAV as file formats and that's also 100% correct. Note: These uncompressed file formats are not the same as codecs.
AIFF is an acronym for Audio Interchange File Format. The format was developed by Apple in 1988 as an extension of the IFF format created by popular video game creator Electronic Arts. AIFF files were originally used on Macintosh computers as the equivalent of WAV files on Windows based computers. Today AIFF files are supported by most popular music playback applications on Windows and OS X. AIFF files support embedded metadata such as album art, artist, and track title. Many popular playback applications can read and write embedded metadata in AIFF files. AIFF and AIF files are exactly the same. Using the technical description from above, the AIFF container / wrapper stores the metadata (album art, artist, track etc...) and any additional information required and simply holds the uncompressed PCM audio data inside this container. During playback the AIFF container is opened by the playback application to access the uncompressed PCM audio data.
WAV is a short name for Waveform Audio File Format. WAV was developed by Microsoft and IBM and released in 1991. WAV files are supported on nearly every operating system and turnkey music server available. Contrary to popular belief and experience WAV files can store metadata. However, very few playback applications can read or write embedded metadata in a WAV file. For example iTunes cannot embed album art into WAV files. Using the technical description from above, the WAV container / wrapper can store metadata (although not in most end user systems) and simply holds uncompressed LPCM audio data inside this container. During playback the WAV container is opened by the playback application to access the uncompressed LPCM audio data.
Lossless compression involves a codec and a container/file format. The codec and container usually go hand in hand. An audio codec is simply an algorithm or program that COmpresses/DECompresses, frequently PCM, audio data.
Popular combinations are:
Codec - Apple Lossless Audio Codec (ALAC)
Container/File Format - M4A
Codec - Free Lossless Audio Codec
Container/File Format - FLAC
Codec - Windows Media Audio Lossless*
Container/File Format - WMA
* WMA is a proprietary codec. FLAC is open and royalty free.
The above combinations usually start with an uncompressed audio file, remove the container (AIFF, WAV, or cda directly from a CD) compress the PCM audio by removing redundant and predictable data then package it into a container such as M4A, FLAC, or WMA. During playback of a lossless file the container is opened, the PCM audio data is uncompressed and reconstructed into the identical PCM audio data that existed before it was compressed. There is much debate in the audiophile community about whether lossless compression results in deteriorated sound quality. The debate centers around the playback application and computer's ability to decompress a lossless file on the fly during playback. Regardless of one's position on this issue the fact remains that lossless compression as a data storage file format does not alter the original data. For example a WAV file can be compressed into FLAC and decompressed back into WAV countless times without altering the original data. The original WAV file is identical to the decompressed WAV file. Taking it one step further, it's entirely possible to start with a WAV file, compress it into a FLAC file then decompress it into an AIFF file without altering the PCM audio data. The container will have changed but the encapsulated PCM audio (song) remains the same. Two main benefits of lossless compression are smaller file sizes and really good support for embedded metadata.
Lossy compression also involves a codec and a container/file format. The most popular combination is the MPEG-1 or 2 Audio Layer III codec and MP3 container. The major difference between lossy and uncompressed and lossless audio is lossy compression removes PCM audio data, with no ability to recreate this data, to reduce file size. A 10:1 compression ratio is fairly common when using lossy compression. This compression results in the permanent loss of much of the original PCM audio data. Lossy compression uses perceptual coding to throw out parts of the original audio data that are said to be beyond audibility or less audible to most people. Other popular lossy formats include AAC and WMA. AAC and WMA can use the same containers as Apple Lossless and Windows Media Lossless (respectively) but are vastly different in that AAC and WMA are lossy.
What are some playback application choices for a Windows or Mac music server?
What's the best Windows or Mac playback application?
What does bit perfect or bit transparent mean?
Bit perfect and bit transparent are synonymous terms. Bit perfect simply means the audio sent out of the computer has not been altered in any way. Ideally the audio signal should reach the digital to analog converter unaltered whether the converter is within the computer or external to the computer. Once the audio signal has been altered there is no way to regain bit transparency within the computer or in the audio system. The two most common ways audio is altered before exiting the computer are sample rate conversion and volume controls.
Sample rate conversion usually happens unbeknownst to the user. One example of sample rate conversion is when a 16 bit / 44.1 CD quality track is played through iTunes on a Mac and the OS X Audio Midi output is set to 24/96. This upsampling alters the original audio on its way out of the computer. Note: Setting the bit depth / word length to 24 bit does not ruin the bit transparency of the audio as long as the track is 24 bit or less. In other words the bit depth must be equal to or greater than the music being played. The sample rate must be identical for the audio to remain bit transparent.
Volume controls are the other way audio is frequently altered on its way out of the computer. To be safe all volume controls on the computer should be set to 100% or maximum volume. Especially critical are the volume controls within the audio playback application. These must be set to 100% or maximum volume. It is possible to output bit perfect audio if some operating system volume controls are not set to 100% because these controls do not effect the audio output from the playback application. When in doubt set all controls to 100%. Only experienced users should change volume control settings. Depending on the audio output method some volume controls may be appropriately disabled by the operating system.
Do I need a sound card in my computer if I have a USB DAC or any external DAC?
What is a DAC and do I need one?
What's better FireWire or USB DACs?
Neither interface is inherently better than the other. Most important is the design of the DAC and implementation of the FireWire or USB interface. Some FireWire DACs sound better than USB DACs and vice versa.
Items to consider
Is it possible to rip DVD-Audio and SACD discs?
Ripping the DSD audio layer from an SACD traditionally required very expensive professional audio equipment. Currently a PlayStation 3 is capable of ripping the DSD layer from SACD discs. There are very specific requirements and procedures to following in order to rip the DSD layer. The following link has much if not all of the needed information.
More Info -> Ripping SACD With PS3
Ripping DVD-Audio discs is entirely possible and quite simple. Ripping all sample rates from 48 kHz through 192 kHz is no problem with the right software.
Can I play high resolution audio via USB?
Yes USB DACs are capable of accepting audio from 16/44.1 through 24/192. That said, not all USB DACs can handle these sample rates. There are three groups of USB DACs as far as sample rate support goes.
- Group A supports sample rates up through 16 bit / 48 kHz.
- Group B supports sample rates up through 24 bit / 96 kHz.
- Group C supports sample rates up through 24 bit / 192 kHz.
Much more important than support for high sample rates is the design and implementation of the USB DAC. Most use Adaptive transfer mode while a limited number use Asynchronous transfer mode. Some require software or device driver installation by the end user while other require no user intervention and use the operating system's built-in device drivers.