What is sample rate in audio?
When you record music digitally, your analogue to digital convertor takes a certain number of samples of the analogue signal every second. You can think of this as the number of ‘snapshots’ taken to create a digital version of the analogue signal. Sample rate refers to the number of samples taken per second. Sample rate is measured in kilohertz. A sample rate of 44.1kHz captures 44100 samples per second. A sample rate of 48kHz captures 48000 samples per second… and so on.
The number of samples captured per second determines the frequency range that can be captured and reproduced. Owing to something called the ‘Nyquist theorem‘, the highest frequency that can be represented by digital audio is half the value of the sample rate. We call this the ‘Nyquist frequency’. As such, a sampling rate of 32kHz can capture and reproduce frequencies up to 16kHz. A sample rate of 44.1kHz can capture and reproduce frequencies up to 22.05kHz. A sample rate of 48kHz can capture and reproduce frequencies up to 24kHz, etc.
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Is a higher sample rate better?
Much like with bit depth, there is a common misconception that the higher the sample rate, the better the quality of the audio. This isn’t so. Increasing your sampling rate simply allows you to capture higher frequencies. So as long as your sample rate is high enough to capture and reproduce the highest frequency in your audio, then that frequency and everything below it can be captured and reproduced perfectly. Increasing the sample rate cannot improve it in any way.
As you may know, human beings can hear frequencies within a range of 20Hz to 20kHz (though most of us can only hear up to 15-18kHz). As such, we generally work with sampling rates of at least 44.1kHz. That’s because 44.1kHz is capable of capturing and reproducing all of the frequencies within (and even a bit past) the range of human hearing.
So, what’s the best sample rate to use? Well, when it comes to bouncing your song to release to the world, although your digital distributor may invite you to upload songs with a sample rate higher than 44.1kHz, it really isn’t necessary. Because as we’ve already established, 44.1kHz can reproduce all the frequencies that human beings can hear. But what about when it comes to the sample rate that we record at?
Sample rate: 44.1kHz vs 48kHz
You’re probably thinking, if 44.1kHz can capture all of the frequencies within the range of human hearing, then we should record at 44.1kHz, right? Well, you could, and it would probably sound absolutely fine. But I actually recommend that you record at 48kHz. The reason for this centres around something called ‘anti-aliasing’…
Earlier, I mentioned the Nyquist frequency. Analogue to digital convertors are not able to capture frequencies above the Nyquist frequency properly. Allowing your analogue to digital convertor to capture frequencies above this point causes a type of distortion called ‘aliasing‘. Aliasing occurs when frequencies above the Nyquist frequency are incorrectly interpreted as frequencies beneath it, creating an ‘alias’.
To prevent this occurring, analogue to digital convertors use something called an ‘anti-aliasing filter’. This is a low pass filter used to ensure that frequencies in the analogue signal above the Nyquist frequency are filtered out prior to conversion. It was for this reason that the sample rate of 44.1kHz was developed. 44.1kHz provides not only the ability to capture all frequencies within the range of human hearing, but it also leaves room for the anti-aliasing filter as well.
Of course, a low pass filter cannot instantaneously cut off frequencies beyond a certain point. The frequencies are rolled off in accordance with the steepness of the filter’s slope. But if you apply too steep of a slope, you can experience a resonant peak or other unwanted side effects. At 44.1kHz, the anti-aliasing filter’s slope has to be pretty steep. The anti-aliasing filter could use a more gradual slope, but at 44.1kHz, it may start rolling off frequencies within the range of human hearing. As such, 48kHz provides room to use a more gradual slope. For this reason, there is the potential for there to be a slight difference between a recording made at 44.1kHz and a recording made at 48kHz, albeit very minor and especially so with modern audio interfaces.
Here’s the bottom line. I recommend that you record with a sample rate of 48kHz. I recommend that you then bounce down to 44.1kHz for the final release. Recording at 48kHz enables you to record everything within the range of human hearing while leaving ample room for the anti-aliasing filter. I don’t recommend recording any higher than 48kHz. That’s because the higher the sample rate, the bigger the file sizes and the more processing power they require. Plus, as we’ve established, it won’t improve the quality. In fact, there are some that believe that very high sample rates may actually make your music sound worse. Bouncing your final mastered track to release at 44.1kHz again means that your digital audio file can represent everything that it’s possible for a human being to hear.
What sample rates do you like to work with for your recording and bounces? Leave your feedback in the comments below.
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Hi, my guitar effects unit only allows me to record at 48 kHz leaving me little choice but to record at 48 – on a Mac that is (alternately, I can go analog via a line out into my interface, which I believe is not as good as USB?). So my question is that when I am downsampling a 48 kHz project to 44.1 what are the factors I need to consider to make sure it sounds good. Do I need a high quality expensive software. What do you advise. Thanks.
Hey, thanks a lot for your question.
When you bounce the final 44.1kHz file from your 48kHz session, your DAW should handle the conversion for you. As for whether your recording will sound better via a line out or USB, it’s hard to say. The only way to find out is to try both and see if you think that one sounds better than the other.
I hope this helps!