High resolution
By design a CD contains 16 bit samples with a 44.1 kHz sample rate.
This allows theoretically for a dynamic range of 16*6= -96 dBFS and 44.1/2 = 22.05 kHz as the highest possible frequency.
Recordings are often made with a greater bit depth (24) and a higher sample rate.
One of the benefits of computer based audio is that you are not in need of recordings down sampled to CD format.
You can play the original recording at its original bit depth and sample rate (if your sound card allows for it).
A 24 bits recording allows for a dynamic range of 24*6= -144 dBFS
Sounds impressive but CD’s -96 dBFS is very soft and the noise floor of your gear e.g. -110 dBFS will be the limiting factor.
But probably listening to the decay of instruments might reveal a subtle difference.
96 kHz has a Nyquist frequency of 48 kHz.
Sounds impressive too but our hearing stops somewhere at 20 kHz (when we are young).
This sounds like buying recordings containing information above our upper threshold of hearing is like paying a premium for some emperor’s new clothes.
There are reasons why a hi-res recording can sound different.
Down sampling might introduce artifacts
Our tweeters can sound different when modulated with signals < 20 kHz or when modulated with signals > 20 kHz.
Often no audible differences between CD audio and higher resolutions are reported on the internet. Just as no audible differences between CD audio and high bitrate MP3 is often reported. As 1+1=2 some conclude that there isn’t a difference between MP3 and hi-res audio!
You can also find reports like this one:
I am interested in everyone's experience with the quality of various HD Tracks labels in hi rez. I have had excellent results with Reference Recordings, Dorian, Chesky and 2L. But I was very disappointed with the BIS recording of Osmo Vanska's Beethoven symphonies 2 & 7. I had seen rave reviews of the SACD version, but when I downloaded it in 24/88.2 from HD Tracks, the sound quality was nothing special. My RBCD version by Gunther Wand on RCA has better SQ
http://www.audioasylum.com/cgi/t.mpl?f=pcaudio&m=72939
Somebody listening to hi-res and is missing the hi-res sound.
Others chime in; ask for a sample and it turns out that this recording doesn’t contain any signal above 22 kHz.
One of those examples where you pay a premium for a hi-res track and get up sampled CD audio in return.
Unfortunately this is not a single incident.
http://www.audioasylum.com/cgi/t.mpl?f=pcaudio&m=74993
http://www.audioasylum.com/cgi/t.mpl?f=pcaudio&m=72939
http://www.audioasylum.com/cgi/t.mpl?f=pcaudio&m=81291
As long as companies selling hi-res don’t tell you what the resolution is of the source used, you run the risk of being scammed.
These incidents also proof that some can hear the difference between CD and hi-res.
Unfortunately even ‘normal’ downloads can have their problems like an audible vibrato.
Listening with your eyes
There are a couple of tricks to check if a recording is true hi-res.
An obvious one is the frequency spectrum.
Theoretically a sample rate of two times the highest frequency is sufficient to reconstruct the analogue signal (Nyquist frequency) .
Our audible range is 20 – 20.000 Hz. Sampling at 40 kHz is in principle sufficient but there needs to be some additional room for the filtering (transition band).
That’s why CD audio uses a sampling rate of 44.1 kHz.
What ever the sample rate might be, if the spectrum it is cut off at 21kHz the source is probably 44.1 (CD)
A nice overview of a couple of recordings with spectrograms by Fujak.
- Listening with your eyes - Bruce Brown
- Hires Audio - soundcheck's - audio@vise
- The HD music fft atlas reference thread - wgscott
- HD-Produktionen auf dem Prüfstand - Fujak
- The tradeoff of 192 kHz sampling - Mikael Vest and Peter Scheelke - Digital Audio Denmark