Digital recording facts for kids

This screen shows sound levels on a digital recorder (Zoom H4n)

Digital recording is how we turn sounds or videos into numbers that a computer can understand and store. Imagine taking a picture of a sound wave many, many times per second. Each "picture" is then given a number. For sound, these numbers show how air pressure changes over time. For video, they show changes in color and brightness. These numbers are then saved on a storage device, like a computer hard drive or a CD.

When you want to listen to or watch a digital recording, the numbers are read back. Then, they are changed back into the original sound or video. This way, you can hear the music or see the movie. A cool thing about digital recordings is that they don't get worse when you copy them. Unlike old analog tapes, a digital copy sounds exactly like the original!

How Did Digital Recording Start?

Digital recording has a fascinating history, with many smart people helping it grow. Here are some key moments:

• 1938: A British engineer named Alec Harley Reeves invented a way to turn sound into numbers. This method is now called pulse-code modulation (PCM). It was first thought of for phone calls.
• 1943: During World War II, a secret system called SIGSALY was made. It used PCM to send scrambled voice messages so enemies couldn't listen in.
• 1957: Max Mathews at Bell Labs used a computer to create music for the very first time! It was a short piece called "The Silver Scale."
• 1967: In Japan, NHK developed the first commercial PCM machine for recording sound. It could record one sound channel.
• 1970: James Russell created the idea for recording and playing back sound using light. This led to the Compact Disc later on.
• 1971: Denon, a Japanese company, made the world's first commercial digital recordings. These were music albums by Stomu Yamash'ta and Steve Marcus. The Steve Marcus album was the first one released to the public.
• 1972: Denon introduced a bigger, 8-channel digital recorder. It was used to record classical music, showing how digital sound could capture every detail.
• 1974: The first digital recording outside Japan happened in Paris. It was a classical music piece by Bach.
• 1975: Thomas Stockham from the University of Utah made his own digital audio recorder. He started a company called Soundstream to sell it.
• 1977: Sony released the PCM-1 Audio Unit, the first digital recorder for regular people to use at home. You needed a home video recorder to save the sound.
• 1978: Sony also brought out the professional-grade PCM-1600. This machine made digital recording available to music studios for the first time.
• 1978: Telarc used Soundstream's system to record classical music. This became the first US-recorded digital classical album released.
• 1978: A recording by the Saint Paul Chamber Orchestra became the first digital recording to win a Grammy Award.
• 1979: The album Bop Till You Drop by Ry Cooder was the first US-recorded digital LP of popular music with singing.
• 1979: Christopher Cross's self-titled album became the first digitally recorded album to become a hit in the United States. Digital recording was now very popular!
• 1980: The "Red Book standard" was created. This set the rules for how Compact Discs (CDs) would work, using 44.1 kHz and 16-bit sound.
• 1982: The first commercial Compact Discs were made. These included classical music by Claudio Arrau and ABBA's album The Visitors.
• 1982: The first compact disc players were sold by Sony and Philips.
• 1982: Billy Joel's 52nd Street became the first CD to be sold in Japan.
• 1983: CD players and CDs from CBS Records arrived in the United States.
• 1985: Dire Straits' album Brothers in Arms became the first album where CD sales were higher than LP (record) sales. This showed how popular CDs had become!
• 1987: Sony created Digital Audio Tape (DAT), another way to record digitally.
• 1991: Alesis Digital Audio Tape (ADAT) was introduced. It allowed recording eight digital audio tracks at once onto a special video tape.
• 1993: RADAR was the first device that could record 24 digital audio tracks at once onto computer hard drives.
• 1999: Ricky Martin's song "Livin' la Vida Loca" was the first No. 1 song to be fully recorded, edited, and mixed using a computer program called a digital audio workstation.

How Does Digital Recording Work?

Digital recording involves two main steps: turning analog signals into digital data, and then turning that digital data back into analog signals for us to hear or see.

Recording Sound or Video

Here's how an analog signal (like sound waves) becomes a digital recording:

• The sound or video signal first goes into a special device called an analog-to-digital converter (ADC).
• The ADC quickly measures the level of the sound wave many times per second. Each measurement is then given a binary number (a number made of 0s and 1s). The more bits (0s and 1s) used for each number, the more accurate the recording.
• How often the ADC measures the sound wave is called the sample rate. A higher sample rate means the recording can capture higher-pitched sounds.
• The ADC creates a continuous stream of these digital numbers.
• These numbers are then saved onto a storage device. This could be a magnetic tape, a hard drive, a CD, or solid state memory (like in a USB stick).

Playing Back Sound or Video

When you want to listen to or watch your digital recording:

• The saved numbers are sent from the storage device to a digital-to-analog converter (DAC).
• The DAC takes these numbers and turns them back into an analog signal. It rebuilds the original sound or video wave from the number information.
• This rebuilt signal is then made louder (amplified) and sent to your loudspeakers or screen so you can experience it.

How Digital Information is Stored

Different types of digital media use different ways to store the 0s and 1s.

Recording on Discs and Tapes

• For digital tapes, like those used in older camcorders, the part that reads and writes (the tape head) moves in a special way. This helps it record lots of information quickly.
• For optical disc recording technologies like CD-Rs, a laser is used. This laser changes tiny spots on the disc's surface. A weaker laser then reads these changed spots to play back the information.

What Makes a Good Digital Recording?

The quality of a digital recording depends on a few important things.

Word Size (Bit Depth)

The "word size" or number of bits used for each measurement directly affects how clear the recording sounds. More bits mean a more detailed and accurate recording, with less unwanted noise or distortion.

Sample Rate

To make sure the digital recording sounds like the original, the sound must be measured at least twice as fast as the highest sound frequency in the recording. For music, common sample rates are 44,100 times per second (44.1 kHz) or 48,000 times per second (48 kHz). Sometimes, recordings are made at even higher rates, like 96 kHz, for super high quality.

When a Compact Disc is made, the recording is usually changed to the standard CD quality (44.1 kHz, 16-bit). This is part of the final steps in making a song ready for release.

Fixing Errors

One of the biggest advantages of digital recording is that it's very good at resisting errors. When you copy a digital file, it doesn't lose quality like an old analog tape would. Digital recordings can stay perfect even after many copies, thanks to special ways of detecting and fixing any small errors that might happen.

See also

In Spanish: Grabación digital de sonido para niños

• Phone surveillance