Have you ever considered to record at a higher sample rate than you normally do? Have you actually done it? If not, I am going to give you a bunch of reasons why you should! Let’s go!
What is “Sampling Rate”?
Digital audio carries samples of an analogue electrical signal which have been converted to the digital domain through a process called “Sampling” via an A/D (Analogue to Digital) converter. The speed of the sampling process per second determines the sampling rate.
These samples are a sequenced representations of 1s and 0s, encoded in a binary file of information which then the computer can decode back to audible information, by using a D/A (Digital to Analogue) converter, and this way reproduce the original signal that was encoded during A/D conversion.
After a signal enters your audio interface’s preamp, after gain staging, it will then be routed internally to the A/D converter to “sample” the electric signal that the microphone translated from the acoustic pressure it received. This is the sampling process in a bit more detail and is essential to the quality of the digital recording we are capturing. You have heard of these sampling rates before for sure. 44.100 Hz, 48.000 Hz, 88.200 Hz, 96.000 Hz, 192.000 Hz and goes on. These numbers indicate how many samples per second are stored in our computer’s hard drive for a single second per audio channel. The higher the number, the higher the resolution, although there is a silver lining here.
The Nyquist Theorem
There was a Swedish electronics engineer called Henry Nyquist. He migrated to America later on so he is also known as Harry Nyquist. Nyquist was a very clever man who developed a very interesting theorem which is, till today, one of the basic fundamentals of digital audio.
His theorem, in simple words, states that the Sampling Rate has to be double of the highest frequency we want to reproduce in the digital domain while converting an analogue signal. We, humans, can hear frequencies between 20 and 20.000 Hz, so if we were to reproduce that range in full, we would at least required 40.000 Hz as the sampling rate. This proves that the lowest sampling rate currently in the professional audio industry, 44.100 Hz would suffice for a professional recording to be produced. However, there are a few benefits in recording in higher sample rates than 44.100 Hz.
Fact: 44.100 Hz is the sample rate CDs and Video Cassetes used in order to store and reproduce digital recordings.
Benefits of recording in high sample rates
The most important is the elimination of the aliasing effect. Here we go!
Sometimes you might have a signal coming in from a microphone to your interface that goes beyond the limits of the 44.100 Hz sampling rate. That might be happening because of a wider spectral content that the microphone have captured during the recording passed onto the signal to carry. This causes an effect called, Aliasing. To prevent it from happening, our audio interfaces remove extra frequency components before the signal converts to digital by applying an anti-aliasing filter. However, most of the A/D converters do not follow the Nyquist theorem to its full extend. That leads to implementations of the anti-aliasing filter that become active slightly above 20.000 Hz. This causes any frequencies or harmonics above the half of the sampling rate to be aliased back into the recorded signal at a lower frequency instead of being discarded. This, naturally, produces unwanted anharmonic distortion which our human ears can easily identify.
The A/D converters are designed this way only because they assume there is not going to be a lot of harmonic-rich content in high frequencies that is going to be recorded frequently and therefore there is no need for a better implementation of the anti-aliasing filter. However, this changes completely when string or brass instruments, even cymbals, are to be recorded, especially when close mics are involved, as these instruments due to their design can emit very high frequencies and harmonics. On these occasions it is very common to get artifacts recorded in your signal due to these aliasing issues appearing on the top end of your signal’s frequency response and feeling like some kind of harsh distortion. They are even more likely to be noticeable if the recording happens close to the maximum digital headroom which is 0dBFS. Now, if you move your recording to higher sampling rates, such as 96.000 Hz for example, any aliasing that might occur and sneak into the actual audio signal, will appear in frequencies way above the human hearing limit, thus eliminating this issue completely!
Never ever ignore the fact that aliasing might be there as it has the potential to ruin a great recording! Further to the reasons why you should record and work in higher sample rates:
Working in 88.200 or 96.000 Hz can also improve system latency. This is because the same buffer size will process more information in the same amount of time halving the latency time! For example, a 128 packet size buffer will be carrying 48.000 samples per 1 second at 48.000 Hz, but double the amount at 96.000 Hz as each sample will last for half the time.
Having more samples in you audio files can also help with stretching them! This is great for sound designers as it allows the recording to contain more information (samples) and therefore stretched with more clarity than if they had the same manipulation at a lower sample rate.
Down sides of recording in high sample rates
There are down sides as well here, the higher the sampling rate, the larger the audio files stored in our computer, however, nowadays with SSDs any speed issues are out of the picture and with large capacity HDDs storing issues are in the past as well.
Higher sampling rates will also cause your processor to work more but that ties down with the latency benefit mentioned above. More samples processed in the same amount of time can only overwork your CPU, but again, fast CPUs with multiple cores should have no problems in managing this workload.
Conclusion in a few words
It seems as the down sides are very easily countered and if we calculate in the benefits in the greater picture, I don’t see why shouldn’t we all be recording at higher sample rates.
What are your thoughts? Are you going to be recording at a higher sampling rate from now on? Let us know in the comments below!
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