RJ Yenesel is a seasoned sound tech in the video production NYC scene. Some of the productions he and our other crew members have worked on can be found here.
Like many terms referring to digital audio, “Sample Rate” is one often thrown around and not clearly understood by many who use it. They may not know exactly what it really refers to.
The question is a simple one, the answer, however, is a bit more complicated. In short, “Sample Rate” refers to the number of times a piece of digital audio is recorded per second. The higher the sample rate the higher the frequency it is possible to record in.
This is not to be confused with the sampling size, which is associated with the maximum value. Sample rate can be measured in Hz – Hertz or more commonly kHz – kilohertz. When recording, you will need two certain frequency points to dictate the high and low end of the spectrum.
The common thought is that most humans are able to hear between 12kHz and 20kHz. According to something called the Nyquist Limit, the sample rate should always be at least twice that of the highest frequency being recorded.
To quote “Exploratories” at Brown University:
“The Nyquist limit gives us a theoretical limit to what rate we have to sample a signal that contains data at a certain maximum frequency. Once we sample below that limit, not only can we not accurately sample the signal, but the data we get out has corrupting artifacts. These artifacts are ‘aliases’ “.
This explains why CDs are at 22 Hz frequency and have a sample rate of 44.1kHz. It is this basic principle that explains why 44.1 is thought of as the “standard” sample rate in CD’s. The next question that naturally arises is why not record in a higher sample rate? Logical thinking would dictate that increasing the sample size would naturally increase the quality.
Hard drives are cheaper and bigger than ever so file size is less and less of an issue. However, the reality is not as simple as that might lead you to believe.
Though recording at 96 kHz and above is possible it may not be the best idea.
First, increasing the sample rate increases the file size. File size is still a consideration for all digital audio formats and if there’s no discernible difference why ever bother with a larger file size?
Second, using a super high sample rate can lead to more errors, especially with digital signals being sent to analog sources.
Third, is there any discernible difference when using a higher sample rate?
This is a disputed topic and there is no “right” answer. Theoretically, using a super high sample rate such as 96kHz will be a waste for a majority of listeners.
The added sample rate will be capturing much audio that is far above the frequency a human ear can actually hear. Those inaudible frequencies take up a lot of unnecessary space for virtually no benefit.
Now the upside of higher sample rate is that the chance of losing higher frequency is drastically reduced. Another factor is that even though your ears may not pick up frequencies beyond 48 kHz, they may pick up on the harmonics.
For most people the real question is at what sample rate should they record?
Again there is no right answer but for most professionals the current benchmark is 48kHz. There are a number of reasons why 48kHz became the standard for film. The main reason is that 48kHz gives enough headroom to catch most higher frequencies on the audible spectrum. Also, 48000 is divisible – 24, 25, 30 and for interlaced television 50 or 60.
These are common frames per second increments used in film production. 44.1 is fine for CD’s but when dividing by frames per second you need a round number to perfectly sync. The table below will help explain why.
- 48,000Hz / 30fps = 1600 samples / frame
- 48,000Hz / 24fps = 2000 samples / frame
- 44,100Hz / 30fps = 1470 samples / frame
- 44,100Hz / 24fps = 1837.5samples / frame
As you can see, when divided 44,100 Hz at 24 frames per second comes out to a number that is not whole. For syncing and editing purposes whole numbers are ideal and easier to work with. This also explains why 96 kHz is the next logical step.
Hope the above was helpful.
It certainly gives us pause!
RJ is the in-house sound tech at American Movie Company. To utilize his expertise in your next Video Production NYC project, be sure to visit our website.