hello everyone this is amir from audio science review
this is another episode in looking at what's inside high resolution music.
this analysis is a little different in that it's by request to look at the high resolution samples
provided by the great label 2l, the nordic sound, as you can see their website over here
they distribute pretty high quality music but i know the service they provide which is wonderful
for the community is this sampler page where you can actually download music for free at
practically every sample rate and resolution that you might be interested in all the way from cd
quality to dxd and stereo to 352 kilohertz sampling rate so it makes for a wonderful
workbench to look at what's inside high resolution music they're nicely tell you
what the source format is in this case is the dxd so this large file at 410 mega megabytes is the
original master in stereo then their versions in in stereo i have the 96 Kilohertz version
and i've also downloaded the mqa and cd so let's go ahead and look at the these files in addition
i'm going to start with 96 kilohertz sampling rate and let me move this back to somewhere interesting
and before i even play the music if you've watched my previous episodes you already see the problem
um look at these three peaks in here they're occurring 38 kilos on up and obviously they're not
musical information as i've explained before music has this nice exponential roll-off more or less
and there is no musical instrument that just generates these high very narrow pure tones almost
signals way into ultrasound whoever produced and mastered this music just like me and the
rest of you can't hear those so what they didn't hear they didn't catch but they should have just
done this simple objective analysis that this window of frequency analysis exists in every
audio application so they could have just pulled this up found these and eliminated their sources
what are the sources the pure ones again as i've explained before probably the scan rate of
monitors bleeding into the sensitive inputs of the analog to digital converter these wider noise ones
are less pure you know there could be alarms in the building or if it's captured from tape
which i don't think this one is um it could have been bias signals that are used on real-to-real
tape recorders but regardless it's not our job to discover what they are it is theirs they
could easily turn equipment on and off and until these peaks go away and not deliver these to us
another nice phenomenon we see this good learning exercise is that as we get close to our
final frequency of 48 kilohertz which is the bandwidth we can have in a 96 kilohertz sampling
you can see this nice anti-aliasing filter that necessary to get rid of what is called aliasing
and it pulls things down to -180 dbfs which is great so that's natural that's good
what's not good is this so let's go ahead and play the music and see if we can figure
out what the usable spectrum of music is how much of this we really need it
so clearly this part is going up but if if we let it play we see that
it actually does use uh the rest of the uh most of the rest of the spectrum also
let it get louder see you can see this part is jumping in correlation with music and that's
important lesson to learn music is not a random thing an instrument of plays at this frequency
has overtones that play here and the two have to be correlated if there's nothing here
then there's just noise but a real instrument generating high frequencies
will extend here is a good example you can see how naturally extends so i'd say eyeballing it
about 34 kilohertz is is what we need to preserve doubling that to get the sampling rate that would
have been 68 kilohertz we don't have 68 killers uh sampling air 8 and the nearest one would be
88 kilohertz so if this kind of music or the original capture should have been 88 kilohertz
and uh that unfortunately would have captured some of these tones um but
wouldn't have generally delivered to us bunch of extra noise now here the extra noise 88 kHz
the difference between 88 kilos and 96 kilos is not that large but now let's go to the
original master and uh see how wasteful this is um so this horizontal scale is hugely expanded this
is 352 kilohertz sampling so the bandwidth is now half of it or 180 kilohertz or so
and uh if we go back to the previous display the previous display truncated around here
we still see our original ultrasonic tone in here still present and but what's right after
that we see this hugely rising noise pattern and that's typical of low bit rate of one bit sampling
because we don't have sufficient number of bits normally tons of distortion would be generated in
the audible band there's a process called noise shaping where we take noise out of the audible
band and shove it into ultrasonic range the idea being that we can hear noise in the audible band
but we can't hear it in the ultrasonic range so all the noise has been emptied out of here
and shoved into ultrasonic by definition then we don't want to play this this is noise that
is not musical information it should be thrown away and the idea was that we don't hear it and
throw it away indeed some SACD players or i don't know if all of them have a selectable
filter to actually analog filter to actually get rid of this noise and this hash that's coming out
yet in the case of high resolution digital download we're now handing all this to
users and people happily go for the larger number being better 352 is much nicer sounding that 96
kilohertz so let's get all that and attempt to play that so nothing good comes out of playing
this noise on your stereo the amplifier may oscillate make it distort your twitter may
cook may distort may cause intermodulation it may actually generate distortions in the audible band
or may do nothing and that's the best case situation where it does nothing
no reason to distribute all this no reason to originally capture that such a high sample rate
again an 88 kilo sampling rate would have been plenty would have been just nice and
it would have truncated everything to the right so no goodness comes out of this
now scaling all the way down to what would have been a cd release let's go ahead and listen to
the uh 16-bit 44.1 kilohertz sampling so now our horizontal scale uh truncates down to 22 kilohertz
or so and uh let's play this content again and let me see if i can find yeah there we go
oops pay attention to here when it gets quiet
there did you see this peak point now peeking out uh this is a pure tone again or a set of tones
they're not musical there's not part of music we can see the the level of the music is naturally
dropping off but this part is not it gets masked when the music gets louder than it but otherwise
it peaks out this is much more problematic than the high frequency ones because it's in
the audible range it's about 19. some kilohertz was it caused by i don't know uh some instruments
something electronic is generating it uh it's unfortunate i mean that's this is egregious uh
means even in cd we're hearing it let me play that some more there it is you can see it very clearly
uh picking up now it's very low level but you know still we want to have good quality uh there
it is i mean it's just unmistakable that this is not natural nothing here does that you see this
nice exponential clean uh uh roll off and uh she should have sailed into the sunset the same way
so unfortunate unfortunate for sure now lastly let's get into a new form i call MQA master
quality audio it's a new format being introduced and it's claimed to fame is that it encodes high
resolution audio high sample rate audio into low sample rate distribution format in this case 24
bit 48 kilohertz i believe let's open that up now this one is actually 44 kilohertz sampling rate
and but inside this you can actually decode and get the what used to be above here and uh
how does it do that well if you go back to the original
display we can see how he's going to do that this area is the audible frequency range
and we you know PCM format which you know 16 or 24 bits is spent encoding this but as we
get to our ultrasonic if you look at the level z in here the 125 dbfs these are very very low
level signals no way do we need to have a dynamic range that describes them all the way up to zero
i've never seen any high resolution content as much of anything uh above these very very
low levels so what we really need is just a few bits to encode the this spectrum that's
indeed what MQA does um if we go back to the MQA signal and uh let me zoom out a little bit
we see what looks like a cd rate but then we see a strange phenomena over here where
they actually the noise floor rises in here why is the noise flow rise in here
because in here MQA actually attempts to encode the information it needs to generate the rest
of the bandwidth to the right and so in that regard it is degrading the cd rate no question
about it this now this is very very low level you know audibility is a different question than
objective measurement but if we play this we can see that this part of this rising
spectrum did not exist now luckily a lot of it is above ultrasonic and
again for us old folks we don't hear it but the rise starts around 16 kilohertz or so
so clearly the very high frequencies have had a random noise added to them and that information
actually isn't random it's actually uh correlated to what spectrum it wants to generate above
this point but it's been randomized to make his audibility very difficult um you know i haven't
done any double blind tests to see if if i can hear that i believe others have and they sort of
kind of could um set the extreme this this may be audible depending on the content you play
so there's a price to be paid it's backwards compatible MQA is that means just as i'm doing
right now i'm playing this without mqa decoding yet the music plays and i hear it but there's a
compromise in embedding that in here i believe for other content they use 48 killer sampling
which allows this to be shoved further up above the audible bed right now it's at uh 16 killers
so that's it uh hopefully you're finding these uh episodes uh useful uh i know music's about
art and enjoyment and uh you know not about what's going on in here but i think the industry needs to
do a better job in producing and delivering high resolution content to us that's pristine that's
clean um because that's what we pay for we pay a lot more for these high resolution downloads
they're not on sale for little next to nothing on amazon to go and buy the cd
and so we expect and rightfully so uh pristine quality masters
and uh not something that has extra tones in it and noises and what have you okay again
this is amir from audiosciencereview.com talk to you later in a future episode bye