What’s up with sample-rates?

This week I came across an interesting article about using super-sonic sample rates. The article is rather long, so for myself and anyone who is interested I made a question-answer style sum up. The original author is Justin Colletti

What is Nyquist teorem?

Back in the 1920s, the Yale graduate had worked on an early version of the fax machine. By 1947, he had made his most lasting contribution: a mathematical proof that showed any sound wave could be perfectly re-created so long as it was limited in bandwidth and sampled at a rate more than twice its own frequency.

In this case, practice sprung from theory. Nyquist’s Theorem set the groundwork for what would become digital audio. He had provided a mathematical proof that predicts a real law of the natural world. Much like with analog audio recording, the proof for digital audio existed on paper long before it became a reality.

What do anti-aliasing filters do?

Anti-aliasing filters are a basic necessity that was predicted by the Nyquist Theorem decades ago. Go without them and you are dealing with a signal that is not bandwidth limited, which Nyquist clearly shows cannot be rendered properly. Start them too low and you lose a little bit of the extreme high-end of your frequency response. Make them too steep and you introduce ringing artifacts into the audible spectrum.

So what’s up with sample rates?

In theory, rates around 44.1kHz or 48kHz should be a near-perfect for recording and playing back music. Unless the Nyquist Theorem is ever disproved, it stands that any increase in sample rates cannot increase fidelity within the audible spectrum. At all. Extra data points yield no improvement.

Are there any tradeoffs of using 44.1kHz?

In practice, tradeoffs necessitated by anti-aliasing might cause you to lose a few dB of top-end between 17kHz and 20kHz – the very upper reaches of the audible spectrum.

Are there any tradeoffs of using super-sonic sample rates?

But be careful of designers who go for super-sonic sampling rates and set their filters too high. If you include too much super-sonic information in the signal it becomes likely that you will introduce super-high frequency “intermodulation distortion” on playback.

So what is ideal sample-rate?

“Nyquist pointed out that the sampling rate needs only to exceed twice the signal bandwidth. What is the audio bandwidth? Research shows that musical instruments may produce energy above 20 KHz, but there is little sound energy at above 40KHz. Most microphones do not pick up sound at much over 20KHz. Human hearing rarely exceeds 20KHz, and certainly does not reach 40KHz. 

“The above suggests that [even] 88.2 or 96KHz would be overkill. In fact all the objections regarding audio sampling at 44.1KHz … are long gone by increasing sampling to about 60KHz.

But do higher sample-rates really sounds better?

If we’ve tapped out our theoretical benefits by the time we get to a sampling rate 60kHz, then why do some people insist they can hear an improvement when they record at a higher rate? Are they making it up?

Absolutely not – There are definitely some converters that sound significantly better at a higher sampling rate than at a lower one, even in a blind test. But strictly speaking, the problem isn’t with the lower sampling rate – it’s with the converter.

Are there any other practical implications of using 44.1?

My own preference is to work at 44.1, especially on projects that will move from studio to studio and even into band members’ homes, which is so common these days. You never know what kind of computer power and disk speed you’ll be faced with. And, any difference I hear on properly designed converters tends to be less significant than say, a half dB of top-end EQ. In another 10 or 15 years, I might not hear these differences at all. Even today, there are older engineers who can hear fewer of these high frequencies than I can. But that doesn’t mean much: listeningalmost always trumps hearing. And good listening comes with experience.

Conclusion:

In the meantime, keep doing whatever you do and at whatever sample rate you’re doing it at! If we’ve proved anything, I hope it’s that the raw numbers just aren’t that big of a deal.

There are so many more important decisions to make: Whether that dB of EQ is hurting or helping, whether the bridge of the song comes in too early, whether we should move the mic or try another one, or whether we should have chicken or tuna for lunch.

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