What is Digital Signal Processing?

Digital Signal Processing (DSP) is a way of changing sound using computers. It is used all the time in modern music and audio. DSP takes real sound and turns it into numbers. Then it uses math to change those numbers. This changes the sound in different ways. Then it turns the numbers back into sound that we can hear.

Before DSP, audio engineers had to change sound using physical things. They used microphones, tape, mixers, and effects units. These all worked with the actual sound waves in the air. This was called analog audio.

With DSP, audio is in the computer. The sound is represented by numbers. Special computer chips can do math very fast. They can add, subtract, multiply and divide the numbers. This changes the sound in many ways. It can make it louder or softer, higher or lower pitch, add echoes, cut out noise, and many other things.

Analog to Digital Conversion

The first step in DSP is getting the sound into the computer. Sound in the real world is analog. It is continuous. This means it is always changing smoothly over time.

To get analog sound into a computer, it has to be turned into numbers. This process is called analog to digital conversion (ADC). It is done by a special circuit called an analog to digital converter.

The ADC measures the sound many times per second. Each measurement is a number that represents how loud the sound was at that tiny moment. The more measurements per second, the more accurate the digital version is. This measurement speed is called the sample rate.

Each measurement also has a certain accuracy. This is called bit depth. It’s like how many digits each number has. The higher the bit depth, the more detailed each measurement is.

Common sample rates are 44.1 kHz (44,100 times per second) and 48 kHz. Common bit depths are 16 bit and 24 bit. Higher sample rates and bit depths mean better quality, but also bigger file sizes.

DSP Algorithms

Once the sound is in the computer as numbers, DSP can start. The numbers are fed into DSP algorithms. An algorithm is like a recipe. It’s a set of steps that does a certain thing to the numbers.

There are many different DSP algorithms. Each one changes the sound in a different way. Here are some of the most common types:

Filters

Filters cut or boost certain frequencies. A low pass filter cuts out high frequencies. This makes the sound more bassy. A high pass filter cuts low frequencies to make the sound thinner. Bandpass and notch filters cut or boost a certain range of frequencies in the middle.

EQ

EQ is like a more advanced filter. It can boost or cut many different frequency ranges. Each range has its own control. EQ is used to shape the tone of a sound. It can make it brighter or darker, thicker or thinner, and so on.

Dynamics

Dynamics processing changes the volume of the sound over time. Compression makes loud parts quieter. This makes the sound more even. Limiting stops the sound from going over a certain volume. This prevents clipping and distortion. Expansion makes quiet parts even quieter. This can reduce noise.

Time-Based Effects

These effects change the sound based on time. Delay repeats the sound after a certain time. This creates an echo effect. Reverb simulates the sound bouncing around in a room. It makes the sound seem like it’s in a certain space. Chorus and flanging create copies of the sound and change their pitch and timing. This makes the sound thicker and wider.

Pitch Shifting

Pitch shifting changes the pitch of the sound without changing its speed. This can make the sound higher or lower. It’s often used to create harmonies from a single voice or to tune drums and other instruments.

Time Stretching

Time stretching changes the speed of the sound without changing its pitch. This is useful for matching the tempo of different songs or for fixing timing issues in recordings.

DSP in Music Production

DSP is used in almost every part of modern music making. Here are some of the most common uses:

Recording

When recording, DSP is used to get the sound into the computer. The ADC turns the microphone or instrument signal into numbers. DSP is also used for monitoring. The computer can add effects like reverb or EQ to the sound before it’s recorded. This helps the performer hear themselves better.

Editing

Once the sound is recorded, DSP is used to edit it. Cutting, copying, and pasting are all done with DSP. Fades and crossfades are also DSP. More advanced editing like time stretching and pitch shifting also use DSP.

Mixing

Mixing is where DSP really shines. EQ, compression, reverb, delay, and all other effects are DSP. They shape the sound of each track and help them fit together. Automation is also DSP. This is where the settings of effects change over time.

Mastering

Mastering is the final step before a song is released. DSP is used here to make the overall song sound as good as possible. EQ and compression are used to make the song bright, loud, and punchy. Stereo widening effects are used to make the song sound big. Limiting is used to make the song as loud as possible without distortion.

Live Sound

DSP is also used in live sound. The mixing console at a concert is a big DSP machine. It takes the signals from all the microphones and instruments. It then applies EQ, dynamics, and effects to each channel. It also sums all the channels together into a main mix.

The speakers at a concert also use DSP. Crossovers split the sound into different frequency ranges for each speaker. Time alignment makes sure the sound from all the speakers arrives at the same time. EQ and dynamics processing shape the overall sound to fit the venue.

Advantages of DSP

DSP has many advantages over analog audio processing:

Precision

DSP can be very precise. Parameters can be set exactly. This is harder with analog knobs and faders.

Recall

DSP settings can be saved and recalled exactly. This is useful for saving and loading different sounds. Analog settings are harder to save and recall exactly.

Flexibility

DSP can do things that are impossible with analog. Extreme settings, complex automation, and advanced algorithms are all possible with DSP.

Non-Destructive

DSP is non-destructive. You can change the sound as much as you want without actually changing the original recording. With analog, each step permanently changes the sound.

Disadvantages of DSP

DSP also has some disadvantages:

Latency

DSP takes time. The computer has to do all the math. This can cause a slight delay between the input and output. This delay is called latency. Low latency is important for live playing and recording.

Artifacts

If not used carefully, DSP can cause unwanted sounds. These are called artifacts. Clipping, aliasing, and quantization noise are all types of artifacts. They can make the sound harsh or unnatural.

Learning Curve

DSP can be complex. There are many parameters and settings. It takes time to learn how to use them effectively. Analog gear is often simpler and more intuitive.