In this serie:
Now that we know the historical and technical details that led to the possibility of setting up a recording studio on a computer (if you haven’t done yet, I highly recommend reading Part 1), we can focus on some aspects of digital recording. At the end of Part 1, we switched from recording on magnetic reels (tapes or cassettes) to recording on hard or floppy disks in digital domain, that means there is not anymore a continuous flow of audio events recorded on a magnetic tape, but a flow of binary data, as happens with any information recorded on a computer.
The role of audio interface
The audio interface is responsible for the translation from sound waves into digital representation of the same sonic event.
One of the main functions of an audio interface is to convert sound from physical instruments or microphones (analog) to a form that computers can process (digital). This is called analog-to-digital conversion, or ADC. It is a necessary part of the digital audio workflow.
While real-world sounds are continuous and analog (think of the sound produced by a (physical) instrument or a voice), on the other hand, computers operate in a discrete, binary world. They process information as a series of digits represented in a binary form (ie. as 0’s and 1’s).
Hence, in a digital audio workflow where computers are the main processing engine, the analog signals from instruments or voice (through microphones) need to be converted into a digital form. This is the work of ADC.
Once audio signals have been converted to a digital form using ADC, they can be processed using specialised audio software called Digital Audio Workstations (DAW).
DAWs are extremely powerful software and allow a range of mixing, processing, and production possibilities for digital sounds, and any sort of effects and magic transformations.
But, how do we hear what we are doing if the audio events are just a series of 0 and 1?
Here comes the digital-to-analog conversion, or DAC, which is the reverse process of ADC. DAC converts the binary data to analog signals and so we can hear what we are doing. The audio signal is sent to our headphones through a little integrated amplifier, or to a bigger monitoring system through an external amplifier and loudspeakers.
Almost any computer integrates a sound card, but while these sound cards are adequate for everyday use, they do not produce a quality of output that’s sufficient for many audio processing requirements. The “sound card” may simply be a “sound chip” built into the computer’s motherboard.
This is why audio interfaces play a fundamental role in a recording studio.
Audio interfaces are specialised hardware and software devices that are dedicated to ADC, DAC, and other functions.
Audio interface drivers are a very important part to consider: the fluidity of your work in the DAW will depend on their stability and solidity, and each different interface has its own drivers.
In general, each interface will allow you to select inputs and outputs and the relative volume, but some also offer useful tools such as the audio router shown in the following image: drawing virtual cables on the interface allows the connection or disconnection of any input and output as desired.
You can find more information about different audio drivers in Windows here.
Being specialised, audio interfaces generally produce much better output than computer sound cards and are included in any digital audio workflow where sound quality is important.
Other than being specialised for ADC and DAC processing, audio interfaces offer a range of other facilities, such as:
- They can have multiple inputs through various connection types (eg. XLR, TRS, and RCA connections) for recording voices or analog audio instruments (for example, a bass guitar)
- For this work, they often include high quality pre-amps for microphone or low-level signal boosting
- They can have a choice of outputs for better sound monitoring during the production process
- They can help to reduce latency in the audio production workflow
- They generally produce an overall higher quality of sound relative to computer sound cards
Despite this, audio interfaces (or ADC in general) may not be necessary if a production process does not include any physical instruments or voice (eg. when using only virtual instruments – also called VST): in such cases, there’s no need to convert sound from an analog to a digital form, and obviously there’s no need for ADC.
I think it’s now easy to imagine how a quality sound card will directly influence the quality of your productions; you can have the best computer in the world, ultra expensive microphones and instruments, but if the sound card does not have first quality converters the result of your work will necessarily be poor.
But how are the input signals converted by the ADC and the output signals rebuilt by the DAC? They need a reference to work in sync and return the audio stream needed for listening by ears…Here comes bitrate, sample rate and bit depth.
Digital audio is digital information. That information can be dense or sparse, high-quality or low. Bitrate is the term used to describe the amount of data being transferred into audio. A higher bitrate generally means better audio quality..You could have the greatest-sounding recording of all time, but if you played it with a low bitrate, it would sound worse on the other end.
Understanding bitrate is essential to recording, producing, and distributing audio. To truly comprehend bitrate, you also need to learn what makes up an audio file and what different types of audio files exist.
Just like images vary in quality and clarity, audio files differ in how large they are, how much information they contain, and what role they fill. While there are some exceptions, uncompressed files will contain the most information and therefore have the highest bitrate. Compressed lossy files generally have the least amount of information and therefore a lower bitrate.
The sample rate is the number of times in a second an audio sample is taken: the number of instances per second that recording equipment is transforming sound into data. Most digital audio has a sampling rate of 44.1kHz, which is also the sampling rate for audio CDs. This means that the audio is sampled 44,100 times per second during recording. When the audio is played, the hardware then reconstructs the sound 44,100 times per second.
Those individual samples vary in the amount of information they have. Bit depth is the number of bits in each sample, or how information-rich each of those 44,100 pieces of audio is.
A high sample rate and a higher bit depth both increase the amount of information in an audio file, and likewise increase the file size. Just like some photos have a high resolution, audio files with a high sample rate and high bit depth have more detail. Having more detail generally requires a higher bitrate.
Why these boring details? Ye,s they are a bit boring, but they will be less boring when you buy an audio interface. They are not all the same, although there are an infinite number of models and brands.
Virtually all of them offer so-called CD quality (sampling rate of 44.1kHz, bit depth 16 bit) which is a standard, others will offer higher resolutions (personally for my recordings i use a resolution of 48.000 kHz at 24 bit depth).
It is a good idea to find the best setting that your workstation can manage effectively. It is completely useless to choose the higher resolution that your audio interface makes available, if the computer can’t handle the produced files, because they are too big for the available CPU and RAM. Each track in your DAW requires hardware resources, then they run out quickly. Don’t kill your computer, it’s your friend.
In the next episode we will talk about another fundamental element of our studio, the DAW. Because without software what do we do with hardware?