Liquid Music: how it works
Digital recording (in brief)
Let it be clear that digital recording is simply taking a sample of an analogue signal. Sampling according to the audio CD standard means collecting 44100 samples each second (44.1 KHz). Each sample is assigned a number value corresponding to the amplitude of the analogue wave at that fraction of a second. The CD audio standard uses 16 bit binary numbers to assign amplitude values: an electronic device can only understand “on” and “off”, something we humans represent with “1” and “0” in our binary numeral system (which is based on only two digits instead of 10 like the decimal system). “16 bit” means we have 216 = 65536 digits – different values that can be assigned. It seems a big figure at first glance, but it isn’t. Even if, on each second, we can assign the 44100 samples one of the 65536 values, we will always obtain something like what’s depicted in the diagram at left: a “saw-tooth” signal in place of the original analogue wave. The CD player’s D/A conversion circuits do what they can to overcome this and other issues of digital audio. The most important is the “jitter”: a normal DAC’s task is to recover each of those 44100 sound samples, assign one of the 65536 amplitude values to each, and place each of them exactly where (in terms of time) they belonged, exactly on the instant the A/D sampler (the digital recorder) did collect them. In a few words, the DAC’s “clock” must be able to synchronize to the clock of the original signal. It never happens, the discrepancy is always there and can just be attenuated, not canceled. This makes a DAC a quality one, the more it is able to reduce jitter (and other typical digital audio issues), the better the DAC performance. Today this is considered much more important that the loss of some interpolatable data. A more radical solution is improve the CD audio sound at the source by elevating the standard. Today, digital audio could take advantage of technologies such as the Super Audio CD (SACD), the DVD Audio or the HDCD, a kind of audio “Blue Ray”. This standards have increased both the sampling frequency and the bit depth of the digital recording process, but none of those standards have really took over. It is hard to imagine now, in the era of Internet and the iPod, a high definition music market that would prompt us to replace our old CDs with a new format as it happened to vinyl records with CDs (like it’s happening with DVD and Blue Ray discs). Now the future is downloading music files, maybe high definition ones: the sampling can be made at 20, 24, 32 bit depth and at 48, 96, 192 KHz. The file size increases but the audio quality improves. Downloading large files is no big deal today. Once the new optical dic formats are dead, what remains is the portable music player …and the computer.
We all have the best digital source at home…
Some might be surprised, but a computer, even a laptop, can be a damn serious digital source in our HiFi systems. Think about it: internal hard disks don’t suffer the same reading precision issues of optical media such as CDs and DVDs. On the contrary, they are way more silent and precise. Your computer’s CD\DVD-Rom player has a very good mechanics. But you’re not supposed to just plug in the computer’s audio output to the amplifier. The right thing to do is ripping digital audio data out of our CD’s to save them in a lossless format (no mp3s!) on the hard disk (better if a fairly-sized external unit) for playback. Today’s external DAC units that can be connected to the USB port make the PC a very nice digital source for our HiFi, maybe the most immediately available for many of us. Since 2007, Apple Macintoshes all have a toslink optical output to connect to an external DAC (you can also use the Firewire port). Just by ripping our CDs into lossless files in the internal disc we can improve the audio performance, especially if the D/A converter within our CD player in not very good. Simply, hard discs do not vibrate like an optical disc and its magnetic reading system does not lose data like the CD’s laser beam. For further precision and reliability we could think of using modern solid state hard disc (flash memories just like USB pens or memory cards for digital cameras). They radically solve all the issues due to moving masses. It sounds nice to be able to manage all our music collection from our PC. If we also consider the opportunity of downloading high definition musical files up to 192 KHz and 24 bits, the CD standard lags way behind, at least in theory. From several points of view, a computer as digital audio source is probably the most reasonable choice. There is the problem of safely storing an ever growing amount of music files, sam as for digital photos and videos. This could make us wonder whether this is really the most comfortable way. Another consideration to be done is: would a classy, top-rated CD player really be surpassed by a hard disk based system? Maybe some very serious CD players would not show many problems when compared to high definition files playback.
But not all recordings are the same…
Finally, if we really don’t feel like using a PC or if we just cannot do it, a good, few-years old used CD player, carefully selected among the brands named above, can surely give us a lot of HiFi music to enjoy. Even a modern DVD/Blue Ray multi-format player particularly focused on audio quality like those from Oppo or Cambridge Audio, can be a reasonable choice (we would also satisfy our cinematographic needs). Spotify, Apple Music and Google Play can offer most of the existing music for 10 bucks a month. It makes you wonder who would possibly still buy CDs or vinyl records.
But not all recordings, even from famous artists, no matter if on CD or vinyl, are made the same. Unfortunately, it is not uncommon to stumble upon recordings (even modern vinyl issues) produced according to a kind of fashion that has been spreading in the music industry in the recent years (unbelievably, with the agreement of some musicians!): an ever growing compression of the music signal.
A musical piece is made of different sections that can have vey different volume levels. Even during the same section of the track we could have a drum hit so intense to be at much higher volume than the section’s average. The difference in volume between the lowest and the highest volume peaks is called dynamics and it is measured in decibels (dB). A live recording may result in vert high dynamics, that is the volume differences between the moments played low and high are very large. When listening in your car or with mobile players and headphones, the high noise background may hide the low volume sections. The music industry’s solution has been to compress the music signal in order to decrease those volume differences (the so called “loudness effect”). It as become such a mania that some recordings have just 2 or 3 dB dynamic range, compared to the 90 dB a CD would be capable of! Today a recording with 15 dB dynamic range is to be considered a good one! In the 80s we could easily find double that. Therefore, the quality of the recordings is very important, being it digital or analogue. It is also obvious that the most important thing of all is the artistic content. Old masterpieces from the history of music are certainly to be listened to regardless of the sound quality, since they are part of. For the above reasons, we should pay much attention to remastered recordings, often worse than the originals. Unfortunately, many modern recordings, due exceptions made, are affected by high dynamic compression.
The audiophile’s life is not easy…
Article about dithering on tnt-audio.com to better understand digital issues
Pleasurize Music Foundation spreads the knowledge of dynamic compression in modern recordings.
Loudness war on tnt-audio.com
Apple iPod music player measurements on stereophile.com