Sample Rate vs. Bit Depth vs. Bit Rate: What are they?

Sample Rate vs. Bit Depth vs. Bit Rate: What are they?

Posted on


You’re looking to dive into the world of audiophilia, and you’re instantly bombarded with terms that you don’t know. Hey, it happens to all of us! The best thing to do is to start slow and get your toes wet with some of the basics. On your journey to being an audiophile, you’ll run into these terms often: sample rate, bit depth, and bit rate. What do they mean and why should you know them? Let’s dive in!

Before we shove off, the audiophile life can drain a wallet in a heartbeat. Firstly, a simple audio setup can consist of a pre-amp, amp, DAC, streamer, and sometimes more. It seems like you need a ton of devices, and they can be rather expensive! Don’t let that scare you away, however. Being an audiophile isn’t about paying $3,500 for fancy equipment.

We have a guide to read before you pay a ton of money for expensive audio devices. It educates you on some of the things to know before swiping your card. Be sure to check it out.

What is sample rate?

Being an audiophile means paying attention to more of the seemingly random numbers on audio equipment boxes and websites. Among these numbers, you’ve probably noticed numbers like 44.1kHz, 48kHz, 96kHz, and 192kHz. These are called Sample Rates. This term is pretty simple to understand if you think of an audio file as an image.

When a digital camera takes a picture, light falls on the camera’s sensor for a split second. The sensor splits the light up into little packets of data, and each packet is different. These little packets of data are better known as pixels. The number of pixels per square inch on a picture is called its resolution.

Well, think of sample rate as the resolution of an audio file. Sound waves are divided into small packets that each have their own unique data. Only, these packets are called Samples. The rules of pixels and samples are similar. The more pixels crammed into a square inch, the higher the resolution, and the sharper the image. Well, the more samples crammed into a second, the higher the sample rate and sharper the audio.

When you record audio, your microphone converts the sound waves into an electrical signal. That signal travels to your device’s ADC (Analog to Digital Converter), which is the opposite of a DAC (Digital to Analog Converter). The ADC takes samples of that electrical signal and then converts it into a sequence of 1s and 0s. Those then become your audio file.

Standard sample rates

There are different standard sample rates, and they are listed above. You’ve often seen 44.1kHz, this is what’s used in “CD quality music”. It means that each second of audio has been split into 44,100 samples. 44.1kHz is a pretty standard sample rate across the audio industry. Think of it as the audio equivalent of 1080p. It’s plenty sharp for average listeners, and much of the music you hear has the sample rate. If you listen to MP3 files, then you’re most likely listening to music with this sample rate.

Next, there’s the slightly higher 48kHz. Just like 44.1kHz, 48kHz is pretty standard across the board. It’s a slightly higher sample rate, which means that the audio will sound a little clearer. 48kHZ is another standard that most of the industry uses. When composers and audio engineers are making music, they want to make sure that they aren’t taxing their computers too much. Using higher sample rates puts more of a load on the computer’s processor, so this is why some people stick to 44.1kHz and 48kHz.

Also, if you’re an Android user, then you should be familiar with this sample rate. The system automatically converts everything to a sample rate of 48kHz, as opposed to iPhones which top out at 192kHz. Even if the audio has a higher sample rate like 96kHz, the system will downsample it to 48kHz. There are only a few apps that bypass this limitation, and Tidal and QOBUZ.

The next standard is 96kHz. It’s twice the speed as 48kHz, so it’s twice as sharp. You’ll see that some of the higher-quality audio gear can push audio at that sample rate. If you’re an audiophile, then you’re likely to tell the difference between 96kHz and the other sample rates.

Lastly, we have 192kHz. Again, it’s double that of 96kHz, and you won’t really find any music recorded in a higher sample rate. This is for people who want the absolute highest sample rate that the industry can offer.

Why is 44.1kHz special?

Out of all the standard sample rates, 44.1kHz seems to stick out. It’s not divisible by 48, and it’s the only one with a decimal point. So, why is it the definitive CD quality standard? Well, it has all to do with the Nyquist-Shannon theorem. Now, digging too deep into this would turn this into a whole college essay, so we’ll keep it basic.

The Nyquist-Shannon theorem states that, in order for a signal to be accurately reconstructed, it must be sampled at at least twice its highest frequency. The theorem doesn’t only apply to audio, but let’s not go too far into the woods with this one.

The human ear can hear tones as high as 20kHz (20,000Hz). As per the Nyquist-Shannon theorem, in order to properly reconstruct a sound for the human ear, that sound should be sampled at a rate twice that of the highest frequency a human can hear. Since the human ear can hear as high as 20,000Hz, the sound needs to be sampled at at least 40kHz (40,000Hz).

Any lower than that, and the human ear will be able to hear degradation in quality. There are sample rates below 44.1kHz, like 36kHz, 24Hz, and so on. Obviously, you would not want to listen to any music with those sample rates.

As for why the standard is 44.1kHz and not 40kHz, there are several theories and explanations floating around that attempt to explain it. However, none of them seem to land on a solid explanation.

What is Bit Depth?

Much of the time when you see a sample rate, it’s accompanied by another number. You’d typically see numbers like 16-bit, 24-bit, and 32-bit. This number is the Bit Depth, and people typically get this number confused with the bit rate. However, these numbers are completely different.

People also conflate bit depth and sample rate, saying that a higher bit depth leads to higher-res audio. While that’s not technically true, a higher bit depth does lead to better-sounding audio. Why is that?

Let’s take a look at the ADC (Analog to Digital Converter). As you can imagine, the ADC takes samples of an audio wave and converts each of them into a digital signal. Each sample represents one part of the sound wave, and it’s distinct from other samples. The thing is that the ADC’s quality dictates each sample’s accuracy.

Simplified example

So, a good way to go about bit depth is to look at a simplified example. We’ll use a simple sound wave, a sample rate of only 16Hz, an ACD with only four prongs (two on each side, so this is a 2-bit ADC), and an ADC with eight prongs (four on each side).

As a side note, the number of prongs on each side doesn’t always dictate the bit depth. Different manufacturers developed different types of ADCs with different numbers of prongs as bit depths increase. However, for the sake of this article, we’ll keep things simple and have the number of bits correspond to the prongs.

Looking at the graph below, the X-axis is the sample rate and the Y-axis is the bit. We see the simple wave represented on the graph. You’ll notice that this 2-bit signal has four lines on the X-axis. We’ll explain why in just a bit.

Graph #1

Look at graph #2, and notice that there are dots that plot the rough shape of the wave. Each dot sits where the wave intersects the X-axis and Y-axis. If the wave doesn’t land exactly on an intersection, the dot will be placed on the intersection nearest to the wave.

Bit Depth Chart 2
Graph #2

Graphs #3 and #4 will draw a line between the dots. Do you notice how, because the space between the bits is so massive, it’s having a hard time properly graphing the wave? We’re not seeing a proper representation of the wave. Why is it like this?

 

Well, let’s take a look at a graph of our ADC. We see that the chip only has two prongs. As stated before, the microphone converts audio waves into an electrical signal, and that signal travels to the ADC to be divided into samples. Each sample will be a sequence of up to two binary digits (1s and 0s) because there are only two prongs.

2 bit adc

Let’s say, for example, that the first sample will be 10, the second one will be 01, and so on. There are four different possible sequences that a 2-bit ADC can produce (11, 00, 10, and 01). This is why there are four lines on the X-axis.

As the bit depth increases, so does the number of possible binary digits. A 4-ADC could produce 16 different combinations because each sequence can have up to four digits (0000, 0001, 0011…). An 8-bit ADC can produce 256 combinations. To find the number of possible combinations, just take 2 and raise it to the power of the bit depth. So 2² = 4, 2⁴ = 16, 2⁸ = 256, and so on.

Now, let’s look at a 4-bit ADC.

4 bit ADC

The X-axis will be more dense. This means that the dots will be able to more faithfully plot the wave. A 4-bit ACD still has some trouble plotting the wave, but you can see that graph is a bit more faithful.

No one would realistically record a song with a 4-bit or even an 8-bit ACD. The industry minimum is 16-bit audio. A 16-bit ADC can produce up to 65,536 combinations, which would be quite hard to put on a graph. However, a graph like that would be able to properly represent the wave. We have to also take into account that the sample rate would be much higher in a professional ADC.

How does bit depth affect the audio?

As you can imagine, a 2-bit ADC can’t properly reproduce the signal because it has to constantly round it up or down. This is called Quantization. The more extreme the quantization, the more noise you get in the signal. The signal’s amplitude keeps landing slightly higher and lower than the actual wave. This causes random bits of noise. As the audio plays, you hear these random bits of audio build up and become white noise.

This might not be a 1-to-1 comparison, but think about digital noise in a video. You see little bits of color all throughout the video popping in and out. That can be similar to white noise in an audio file.

What is bit rate?

As stated before, people typically mix up bit depth and bit rate. Bit rate is actually a bit easier to explain; it doesn’t require quite as many graphs; it’s actually just an equation.

To get the bit rate, you take the sample rate and multiply it by the bit depth. You then take that product and multiply it by the number of channels of the audio (typically 2). Lastly, take that large number and divide it by 1,000.

So, let’s take a typical example: 16-bit/44.1kHz. Firstly, don’t multiply 16 by 44.1. Since 44.1kHz is talking about 44,100 samples in a second, you should multiply 16 by 44,100. (44,100 × 16 = 705,600).

Take that number and multiply it by 2 since your audio has two channels. (705,600 × 2 = 1,411,200).

The large number you get is the number of bits per second. In order to get a cleaner number, divide it by 1,000, and you’ll get the number of kilobits per second. (1,411,200 ÷ 1,000 = 1,411.2). So, the bit rate is 1,411.2kbps. You might see that when you look at audio specs for a CD or a CD-quality song.

Other typical bit rates you’ll see are 128kbps, 196kbps, and 320kbps. With higher bit depth and sample rates, you’ll get higher bit rates.

Keep an eye open for these terms

The best thing that you can do is familiarize yourself with the lingo. Becoming an audiophile can be a pretty expensive and complicated process. However, knowing about these terms can help out a ton! For example, if you’re in the market for a pair of Bluetooth headphones/earbuds, you’ll want to know what codecs they’re compatible with. Codecs like Qualcomm’s aptX HD tops out at 24-bit/48kHz. If you want a higher-quality listening experience, you’d want to get a pair that’s compatible with that codec as opposed to a codec that caps out as 16-bit/44.1kHz.

Also, did you know that Android has a limit that keeps audio quality from going past 48kHz? That’s important to know if you’re an Android user. Lastly, are you looking to put together an audio setup? Well, you’ll want to know the specs for your DAC, amp, pre-amp, and other devices, and the sample rate, bit depth, and bit rate are among those specs.

Knowing more about the audio going into your ears is the first step on your journey to becoming an audiophile.



Source Link Website

Gravatar Image
My John Smith is a seasoned technology writer with a passion for unraveling the complexities of the digital world. With a background in computer science and a keen interest in emerging trends, John has become a sought-after voice in translating intricate technological concepts into accessible and engaging articles.

Leave a Reply

Your email address will not be published. Required fields are marked *