How to get the Best Audio Quality
How to get the Best Audio Quality
One question that sometimes arises in the forums is "Now I've got one of these things, what settings or tools are recommended if I want to get the best possible audio quality out of it?". The purpose of this section is to answer this question for someone new to the world of Squeezebox and Transporters, however basic or 'low-end' their system might be.
Note that the term "audiophile" is generally avoided here: it seems to mean pretty much whatever you want it to mean! Have a look in the "Audiophile" section of the Slim forums.
This page focusses on settings and standard tools - you won't find discussion of esoteric modifications, strange crystals or green marker pens. Again, try the "audiophile" forum or some of the other Internet discussion forums if this is where you are headed.
What this wiki tells you
I've structured the wiki so that it's helpful (I hope) for technical and non-technical users alike. In each case I will present a recommendation, and why it's recommended. The why section is likely to be technical but I will make sure there's nothing in the why section that is necessary to make it all work - it's purely for those people that want to understand the inner workings (and possibly question the recommendations).
Some of the recommendations might involve spending money: however if you can't afford it you don't have to bother, it's just one of the drawbacks of writing this for the widest possible audience.
The primary recommendation here is to use a lossless format for your songs stored on the server. There are a variety of formats to choose from the table below lists the common formats and their characteristics. The columns below tell you:
- Lossless? - whether the format is lossless
- Compressed? - whether the format is compressed
- Open support? - whether the format has an open community supporting (a factor in its longevity).
- Native support in Squeezebox (SB2 or later)? - whether the format is natively supported in Squeezebox. If it is, the file can be sent over the network without first being transcoded on the server. This reduces server load, and, in some circumstances, consumption of network bandwidth. It also allows seeking – that is fast-forwarding and rewinding within tracks.
- Recommended? - whether the format is recommended (I take into account some other features than just lossless here, but I'll admit this is subjective. Feel free to disagree)
- Other notes? - other information that might help you make an informed decision.
|Format||Lossless||Compressed||Open support||Native Decode support||Recommended||Other notes|
|FLAC||Yes||Yes||Yes||Yes||Yes||Not available on iTunes|
Why not lossy compression?
Lossy compression works by removing some of the audio information that can't be heard by the human ear. Unfortunately not all human ears are the same, yours are definitely different to mine. In particular it is a very subjective judgment as to what can be heard and what can't. In practice many listeners that listen to their music through a reasonable HiFi can hear the sound degradation that goes with a lossy format like MP3. However as the quality of MP3 (and other lossy) encoding increases it is getting harder and harder to detect the difference in real listening tests. So, the arguments for not using a lossy compression are:
- some people can tell the difference in quality - whether you can depends on your hardware and ears.
- a lossy format can never reproduce a lossless format (even if you can't hear the difference)
- you can always create an MP3 or any other lossy format if you have a lossless original. You can't do it the other way round.
- there is a lot of man hours invested in ripping your collection, if you upgrade your HiFi later you might be able to hear the difference, and need to do it again.
- the application you use for ripping MP3's is not too important, however when ripping to lossless it is important to ensure a bit-for-bit accurate rip for it to be truly lossless. See the Audio Extraction Software section below.
- the settings you use for compressing MP3 are massively important so it's worth investing time in finding the best for you. The settings used for a lossless encoding are less critical as the only really affect compression and encoded size.
My own personal example might clarify a bit. My CDs compress on average to 300Mb (FLAC) and about 60Mb (MP3). I have 350 CDs which is approx 105Gb (FLAC) or 21Gb (MP3). A brand new 500Gb drive costs around USD100. So for me I've kept everything as FLAC and I'll probably create an MP3 version as well (which is easy as I have the FLAC original). Also it's taken me about 2 minutes a disc to rip them ie about 700min = nearly 12 hours. Finally as they are FLAC if I ever want to convert to a new format I can automate the process without having to reread all my disks.
Be aware that in the above estimation the 2 mins per CD represents the time it takes for me to get the CD and put it in the PC to start the ripping process and take it out again after. The actual ripping process performed by my PC takes about 8-10 minutes to extract the audio (using EAC in secure mode) and a further 3 mins to convert to FLAC (I rip to WAV). Damaged or dirty CDs may take much longer for the extraction (my worst case so far has been 2 hours, but the 8-10 min quoted is about normal).
Why FLAC not other lossless formats?
The arguments here are not really based on audio quality, so if you have a reason to prefer a different lossless format then you should go for it. However there are some reasons why FLAC is a good choice and it seems to be the primary lossless format adopted by the slim community. Those reasons are:
- FLAC is compressed (for most tracks it reduces the size to about 60% of the original size). This compression does not result in any loss of quality.
- Squeezebox understands FLAC natively so it is very efficient for network and server as only the compressed data is sent over the network.
- Native support also also allows seeking (fast-forward and rewind) within tracks.
- FLAC was designed to be resilient and has built in error checking so can help identify if files have become corrupted etc.
- FLAC has good support for tagging files, which can be read and understood by a wide range of players.
- FLAC is an open format (not owned by any commercial organisation and all algorithms and source are freely available). This means it is likely to be available for much longer.
There is more explanation on the above issues (including the ones not related directly to audio quality) at Beginners Guide To File Formats
Audio Extraction Software
Make sure the software you use to copy your songs from the original CD to the computer you are using is designed for best quality.
- For Windows use Exact Audio Copy (EAC)(Free) or dBpoweramp (better metadata, easier, more secure, not Free)
- For Linux if you cannot run EAC/Windows under Wine then use cdparanoia.
- Mac users are recommended to use xAct or Max which has more features including encoding to multiple formats at once.
You should use these tools configured for highest accuracy ripping: for EAC there is help at http://www.hydrogenaudio.org/forums/index.php?showtopic=30959
It's worth noting however if you have the equipment to rip using EAC or dBpoweramp on a Windows system then these are the best options, in that both have long-standing, top rated reputations. A Pentium II, or even maybe a Pentium I can be used for EAC/Windows ripping as for ripping the speed of the computer is always held up by the speed of the CD drive. You don't have to encode/compress from WAV straight away, and you don't have to do it on the same machine you ripped on. Fortunately these jobs can be done by the computer whilst you sleep.
There is more discussion of this topic in Beginners Guide To Ripping.
The process of extracting audio from your CDs only happens once and if there is a fault there it will remain every time you play your song. EAC and cdparanoia have been written to get the best chance of getting a perfect copy of the audio data on your CD (use EAC in secure mode). In particular they both read data many times and check it with previous reads to make sure it is getting the 'correct' information. It can still be wrong, but it is less likely to be wrong than other tools that perform audio extraction.
Squeezebox version 2, version 3 and the Squeezebox Receiver have very similar audio quality through their analog outputs. The earlier models (SLIMP3 and Squeezebox 1) are now (2008) old and although they are still supported and still work, the audio quality is not the same.
The "audiophile" Transporter model is, as the price tag suggests, a different animal altogether: both the analog and digital output sections are substantially improved on the Squeezebox models. Whether the difference justifies the price tag will depend on your ears, your wallet and the rest of your system!
Wired or Wireless?
Audio quality should not be affected by whether you use a wireless or wired connection to your Squeezebox or Transporter: the connection is either reliable or it isn't, depending on factors like the router, distances, and external interference. The connection from SqueezeCenter to Squeezebox is entirely in the digital domain, so if the 1s and 0s are getting through then you are getting full quality.
If you have an old (pre SB2) Squeezebox then you are likely to be better off wired.
With the pre-SB2/3 units, they did only MP3 and PCM native in the Squeezebox. So if you kept your music in Flac, it had to be decompressed on the server and sent as PCM (or raw .wav file). This uses up a large portion of the real bandwidth available on a 802.11b network. And the SB1 had a small buffer. So dropouts were common problems. This problem gets worse the more SBs you have in your setup. With SB2/3 accepting FLAC natively the bandwidth requirement is less and you can use a 54Mbit/sec "g" network, so much less likely to be a problem.
Note that if you are buying a second hand SB2 or SB3 then there are both "wireless" and "wired-only" models in circulation, check which you are getting.
Which DAC (Digital Audio Converter) to use?
Use your ears.
At some point in the listening process you will be using a DAC, either one built into Squeezebox (use the analog outputs) or standalone external DAC, or one built into an AV Amplifier (both these options use the digital output). DACs vary in quality enormously so choose which one you use carefully.
The Squeezebox internal DAC is a modern good quality converter, so it will most likely outperform the converters in older AV units, and may even outperform a standalone DAC from a few years ago. If you've already been using DACs elsewhere in your system you should try different configurations to see what's best for you.
Comparing the relative merits of (Squeezebox plus expensive external DAC) vs Transporter vs (Transporter plus external DAC) is a favourite topic in the Audiophile forums.
What Settings to use in SqueezeCenter?
Most settings can be changed to your own preferences without affecting audio quality. This section only lists those that have an impact on audio quality.
Make sure the bit rate is set to unlimited (the default setting for new installations).
/This setting is available in the Settings - Players - Audio section of the web interface./
The bitrate is a measure of the amount of compressed information being used, if you use a lossless format this is not of great concern to you. However if you limit the bitrate and your compressed file has a higher bitrate the server will try and use another mechanism to compress it further (for example MP3) and you will then be using a lossy compression format.
Not everyone agrees with this recommendation, and most seem to agree that it's less important than the other recomendations. The recommendation is, when using the digital output, to turn off the volume control that is present in the SB2 and only use the volume control on your HiFi.
/In Settings - Players - Audio set "Digital Volume Control" to "Digital output level is fixed"./
If the volume control is enabled in the Squeezebox then the digital information provided by slimserver is manipulated by the firmware and output through the digital output. This manipulation may cause some loss of information. If the digital volume control is switched off then the Squeezebox simply plays what it receives and your DAC does the job it did before when it was directly connected to a CD transport.
Note, however, that CD sources are only 16 bits in depth and the internal digital signal path is 24 bits - so you can turn down the volume quite a way before really losing any quality. Look for forum threads on this topic.
Additions, Amendments and Corrections
This is an open wiki, if you spot something that's wrong please feel free to change it (whether it's just a typo or something more technical). Similarly feel free to add relevant recomendations. For the most part I'd like to keep this page limited to recommendations that most people would support, so please bear that in mind.
Happily the community seems to be in favour of this wiki and have been providing lots of useful feedback so I can improve it. I'd like to recognise some of that here, so thanks to:
- the users of the audiophile forum (too many to mention individually, but a lot of the info here is from that forum)
- those that have made specific comments to help develop this page: