How good is good enough? Problems galore!
We seem to have a nice discussion here. I'm going to risk setting off further controversy, I hope without causing too much offense.
First of all FMW and MDS are absolutely correct about digital clipping and the differences between analog and digital compression.
Lets go to first principles.
Dynamic range compression means narrowing the decibel gap between the soft and loud passages in the program. On pop radio stations it is carried to the extreme, so that it is all loud. Dynamic range compression can be accomplished by both analog and digital devices. They are called audio compressors.
Now in the digital domain we have another form of compression, which in the lossy forms throws away parts of the program the authors of the codecs in question think we won't notice. Most codecs have degrees of compression that the creator of the file can choose. Compression rates vary from chucking out nearly all the bits to just over half the bits. The purpose is to make the file smaller. If it is audio to be streamed, to reduce the bandwidth.
There are also lossless codes such as FLAC, which is an open codec, Apple lossless and the new Dolby and DTS codecs for HD and Blue Ray video discs among others. These codecs reduce the file size significantly, but not as much as the lossy ones. The difference is that they are code/encode, so when the file is recreated to play back, all the bits are there, and it is CD quality. In my view none of the lossy codecs, even at their highest bit rates achieve anything approaching CD quality. A CD plays back at a bit rate of 1411.2kbits/sec. The maximum bit rate catered by mp3 is 320 kbit/sec and 128 kbit/sec is usually what is on offer! They have the gall to call this near CD quality.
Now a word about dynamic range and signal to noise. The CD has a theoretical range of about 100 db or so. To take care of the full dynamic range takes skill, as digital systems don't clip gracefully but with sudden unpleasant effects, if you really hit the wall, believe me everyone will notice. Why is there a noise floor anyway? In analog systems it is the loudest passages that were always the headache, tape saturation, over modulated record grooves and such. All sandwiched between tape hiss and record groove noise. However in digital systems it is the fade, particularly dying notes, in ambient spaces that are the problem. Digital systems can only right 1 or 0. At a point the program has to choose between 1 or 0, and so there is a signal level were the error becomes 100%! So white noise is added to the program in small quantities. This is called dither. The effect is to allow sounds to fade into the noise floor without having 100% quantitization error.
So what is the point of this discussion? In a word greed. Bandwidth costs money. So in commercial terms, the question becomes how many bits can we throw away before significant numbers of individuals complain.
They get away with it for two reasons. There are few critical listeners anymore. People are listening on the run to ipods via headphones, or low fi docking stations. Everything is pop culture geared. Now here I'm going to get controversial, but I believe audio errors are much less noticeable in popular music than most forms of classical music. An mp3 file at 320kbits/sec is just not adequate when played back through a state of the art reproduction system. I have particular torture tests that I use to evaluate these lossy codecs on my digital audio workstation. On choral music they are particularly dreadful. If it is boys voices, with large organs and or orchestra in ambient cathedral spaces the results are tragic. The bass depth is not there, the ambient envelope is just plain weird, when the choir hits the high descant there is quite often gross twinking, which is really excruciating and lastly there are episodes of stereo collapse.
I was having trouble getting a CD of anthems by William Boyce from Christ Church Oxford. I purchased an mp3 download. It was a complete waste of money. Eventually I found the CD.
I and others have been screaming to the record manufacturers who sell downloads to offer FLAC downloads. Chandos have just added FLAC downloads to their on line catalog, bless them. I hope others will follow. The Philadelphia Orchestra have offered Flac downloads for some time. They are excellent.
What I'm getting at is that we all have to lobby for standards to be maintained and improved, and fight the good enough for most people mentality. The next big frontier is going to be digital radio. I have experience of that in visits to the UK. The BBC Third program has the highest bit rates, however when comparing DAB with FM radio, the FM radio wins on quality by a mile. In the UK analog FM is scheduled for a phase out. British music lovers are fighting a vigorous campaign, to keep FM, or have DAB that is true CD quality. The problem is the broadcasters want put multiple stations on one carrier, and split the bandwidth between them. It's that old greed again.
Everyone stay tuned on this one. Great music and the dedicated musicians who perform it, deserve that we demand, and fight for TRUE CD QUALITY as the MINIMUM standard.
The sound didn't fall apart so I didn't think I was maxing the speakers out (b&w 684s), but there was audible popping of sorts. Was the what amplifier clipping sounds like?
