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The practical side of this...
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Don't think sei was being snarky, but anyways...
PaulBrewer wrote: »That's how I discovered it initially!
But this was when you were warping clips in Ableton Live right? The warping algorithms must treat mp3/wave audio differently or something. If you dropped the 2 clips into a "traditional" sequencer I'm sure they would sync exactly. You might get phasing alright, but thats something you might get with comparing 2 WAV clips anyway and is nothing to do with the tempos...0 -
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PaulBrewer wrote: »That's how I discovered it initially!
I dunno - on your first post I did a command-line LAME encode at the highest settings (not VBR) and then did a double CD deck play triggered by MIDI. Being a lot younger than you and not having worked in the industry/gigged to your extent my hearing is considerably better - and I've 14 odd years of theory/classical training... I mean you clearly know a lot more than me, but its fairly fecking obvious to anyone when something goes out of phase - nevermind someone who DJs
I reckon that there's some weak link - either in your DAW, how you're compressing it or how you're burning it. Surely one of the thousands upon thousands of people who DJ using a combination of CD, Vinyl and MP3 would have spotted the problem? A cursory google and wikipedia comes up with nothing, but I'd be happy to be corrected0 -
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PaulBrewer wrote: »Can anyone explain in layman's terms how MP3 encoding works?
Very very basic and roundabout way of doing it but...
If you've ever delved into audio synthesis, you'll know the basics of what happens when you combine waveforms. If you have a simple waveform, say a saw, and you combine it with another signal 180 degrees out of phase from the original (i.e. the original peaks where the new tone troughs and vice versa) the two tones 'cancel out' each other completely and you get silence.
Most people who are into doing mash-ups or remixes take advantage of this if they're looking to try and extract an acapella from a commercial release - by applying the same principle and laying down a (reversed) instrumental version of the track over the original you can extract a, somewhat noisy, acapella.
This nomenclature for these processes is 'Pyschoacoustics' (i.e. how sounds are perceived), with this particular trick known as 'Auditory Masking'.
So basically, the compression involves using a ruleset based on the human ear (not test equipment) to discard the parts of the waveform that are least audible. The threshold for whats kept is based on the selected bitrate - the higher the bitrate, the more thats kept.
Of course, at the lowest bit rates you then get 'artifacts' that weren't present in the original recording. This is caused by anything with a sharp attack, or sudden interjections in the music (or a shout from ambient silence in speech). The most common objections in music prod is that lower bitrates 'mush' highhats and sharp drum hits, killing them of their clarity and introducing new frequencies via these compression artifacts which can cause dissonance - a problem which compounds the original flaws. If you're recording live conference work, for example, you'll always notice that audience applause sounds like someone pissing on a tin roof at the lower bitrates.
Best way of visually representing it is here
http://en.wikipedia.org/wiki/Lossy_data_compression
Consider someone with cataracts or exceptionally poor eyesight. Those four pictures would look identical. Now imagine an example with four audio files - 128kb, 192kb, 256kb and WAV. In a double blind test I should hope everyone here would be able to spot the 128kb from the 192kb, and the WAV from all of them - but I bet very few of your non-audio inclined friends would.
Of course, this problem was (somewhat) solved by the introduce of VBR mp3 encoding - or Variable Bit Rate encoding. Basically, the quieter parts of the music are encoded at a lower bit rate, the louder and more complex bits encoded at a higher bit rate accordingly. Personally I encode everything on my iPod with 256 VBR which is fine for me. I couldn't be arsed with FLAC or AAC and I would rarely rarely notice the difference between it and an original WAV unless it was classical music played quite loud. (For the record, Rachmaninoff 2, 2nd Movement for testing PA systems
). 0 -
Very very basic and roundabout way of doing it but...
If you've ever delved into audio synthesis, you'll know the basics of what happens when you combine waveforms. If you have a simple waveform, say a saw, and you combine it with another signal 180 degrees out of phase from the original (i.e. the original peaks where the new tone troughs and vice versa) the two tones 'cancel out' each other completely and you get silence.
Most people who are into doing mash-ups or remixes take advantage of this if they're looking to try and extract an acapella from a commercial release - by applying the same principle and laying down a (reversed) instrumental version of the track over the original you can extract a, somewhat noisy, acapella.
This nomenclature for these processes is 'Pyschoacoustics' (i.e. how sounds are perceived), with this particular trick known as 'Auditory Masking'.
So basically, the compression involves using a ruleset based on the human ear (not test equipment) to discard the parts of the waveform that are least audible. The threshold for whats kept is based on the selected bitrate - the higher the bitrate, the more thats kept.
Of course, at the lowest bit rates you then get 'artifacts' that weren't present in the original recording. This is caused by anything with a sharp attack, or sudden interjections in the music (or a shout from ambient silence in speech). The most common objections in music prod is that lower bitrates 'mush' highhats and sharp drum hits, killing them of their clarity and introducing new frequencies via these compression artifacts which can cause dissonance - a problem which compounds the original flaws. If you're recording live conference work, for example, you'll always notice that audience applause sounds like someone pissing on a tin roof at the lower bitrates.
Best way of visually representing it is here
http://en.wikipedia.org/wiki/Lossy_data_compression
Consider someone with cataracts or exceptionally poor eyesight. Those four pictures would look identical. Now imagine an example with four audio files - 128kb, 192kb, 256kb and WAV. In a double blind test I should hope everyone here would be able to spot the 128kb from the 192kb, and the WAV from all of them - but I bet very few of your non-audio inclined friends would.
Of course, this problem was (somewhat) solved by the introduce of VBR mp3 encoding - or Variable Bit Rate encoding. Basically, the quieter parts of the music are encoded at a lower bit rate, the louder and more complex bits encoded at a higher bit rate accordingly. Personally I encode everything on my iPod with 256 VBR which is fine for me. I couldn't be arsed with FLAC or AAC and I would rarely rarely notice the difference between it and an original WAV unless it was classical music played quite loud. (For the record, Rachmaninoff 2, 2nd Movement for testing PA systems).
Very well put. I'm not familiar with the exact nature of how lossy encoding algorithms work, but had an idea that they took advantage of psychoacoustic masking.
I'm not 100% sure of the analogy you draw between out-of-phase waveforms cancelling each other out and auditory masking though. Auditory masking (which mp3 encoding takes advantage of) is a psychoacoustic phenomenon which occurs in the brain and is not measurable (e.g. by spectral analysis) in the same way that phase cancellation is. As far as I know, auditory masking has more to do with adjacent frequencies hiding one another than it does with the same frequencies at opposite phases cancelling each other out. It has as much to do with biology (the way the basilar membrane in the ear works) as it does to do with the physical interaction of sound waves:The phenomenon of masking is often used to investigate the auditory system’s ability to separate the components of a complex sound. If two sounds of two different frequencies (pitches) are played at the same time, two separate sounds can often be heard rather than a combination tone. This is otherwise known as frequency resolution or frequency selectivity. This is thought to occur due to filtering within the cochlea, the hearing organ in the inner ear. A complex sound is split into different frequency components and these components cause a peak in the pattern of vibration at a specific place on the basilar membrane within the cochlea. These components are then coded independently on the auditory nerve which transmits sound information to the brain. This individual coding only occurs if the frequency components are different enough in frequency, otherwise they are coded at the same place and are perceived as one sound instead of two (Moore 1986).
Its a fascinating topic, but its very complex and still isn't understood by science completely, not to mention by me, so maybe I have things arseways. I think auditory masking is the key thing though.0 -
I'm not 100% sure of the analogy you draw between out-of-phase waveforms cancelling each other out and auditory masking though.
Thats exactly what it was though - an analogy. Its more to give people a point of reference from the pro-audio world rather than a scientific basing If you want to do further reading into it, looking into anechoic chambers and impulse response etc... Its beyond fascinating and branches in with a few massively diverse fields - most of them with fairly hefty military applications.Auditory masking (which mp3 encoding takes advantage of) is a psychoacoustic phenomenon which occurs in the brain and is not measurable (e.g. by spectral analysis) in the same way that phase cancellation is... It has as much to do with biology (the way the basilar membrane in the ear works) as it does to do with the physical interaction of sound waves
Agree completely with you -jimi_t wrote:So basically, the compression involves using a ruleset based on the human ear (not test equipment) to discard the parts of the waveform that are least audible
I probably didn't emphasis it enough or, indeed, phrase it particularly articulately... twas a heavy nightIts a fascinating topic, but its very complex and still isn't understood by science completely, not to mention by me, so maybe I have things arseways. I think auditory masking is the key thing though.
I'm a hobbyist - an English major with no leaving cert science subject and pass maths. I'm not particularly heavy on the old Waveforms myself, but the whole area of Audio fascinates me; I'm kicking myself having not stayed on with Physics but I'm afraid arsing about with magnets and bits of string for 2 years kinda killed my passion. If they had handed me an oscilloscope now... 0 -
Thats exactly what it was though - an analogy. Its more to give people a point of reference from the pro-audio world rather than a scientific basing If you want to do further reading into it, looking into anechoic chambers and impulse response etc... Its beyond fascinating and branches in with a few massively diverse fields - most of them with fairly hefty military applications.
Ah cool, that's what I kinda suspected :pac:I'm a hobbyist - an English major with no leaving cert science subject and pass maths. I'm not particularly heavy on the old Waveforms myself, but the whole area of Audio fascinates me; I'm kicking myself having not stayed on with Physics but I'm afraid arsing about with magnets and bits of string for 2 years kinda killed my passion. If they had handed me an oscilloscope now...
I like the whole "audio" side of things myself, especially the digital aspect of it. Having some knowledge of the structure and nature of digitally encoded audio makes the whole area of digital music even more fascinating.
If you want to learn a bit more I can recommend this book. It doesn't cover a lot about the digital aspect of sound specifically, but it gives a great introduction to acoustics and psychoacoustics in general. Acoustics is a very well understood branch of physics but psychoacoustics is much more of a mystery, combining areas of physics, biology, psychology and even sociology.0 -
I'm just after spending 100 quid on lighting books; I'll be doing the same once my paycheck comes in on audio books so that'll be on the list, anything else of note?I like the whole "audio" side of things myself, especially the digital aspect of it. Having some knowledge of the structure and nature of digitally encoded audio makes the whole area of digital music even more fascinating.
I maintain a curiousity in the area, but thats kind of it. Once you get into the heavy maths of sampling-rates and binary encoding I tend to not grasp the underlying concepts quick enough to maintain interest
As it stands, outside of actually playing/producing music, I'm fixated on the social and psychological implications of both the development of the medium and the 'audio' itself. I'd love to say I'm devout, but unfortunately I have a life :rolleyes:
An interesting field of study is the role of pyschoacoustics in video games. Get GTA3 for the PC. Run around a bit. Fire a gun. Fire it in a garage. Throw a grenade from various heights and angles. Now pick up a gun power-up with your eyes closed. Where did the sound come from? Where in gods name did all that artifical bass come from ? It's a cheap trick but an effective one.
That game is about 6 years old. The modelling of faux spatial-discrimination using a fixed-two speaker system (i.e. laptop or tv) has gotten quite complex in the meantime. Games are going jowl to jowl with movies nowadays in a number of areas - motion tracking, CGI and budget to name a few. The role of music and general audio has never been more important, although some serious technical limitations remain; predominantly in the handheld market
http://createdigitalmusic.com/2007/04/13/call-of-duty-roads-to-victory-sound-designers-and-composer-interviewedOf course, at the lowest bit rates you then get 'artifacts' that weren't present in the original recording. This is caused by anything with a sharp attack, or sudden interjections in the music (or a shout from ambient silence in speech).
Just this. Obviously it's 'caused' by a separate phenomenon, and anything with a sharp attack exascerbates this. Goes well beyond laymans terms though, and not terribly interesting...to me anyways. Wiki it if needs be.0 -
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