Greg Wurth explains how an analog-to-digital and digital-to-analog converter works. He mentions that there are a lot of details regarding formats such as sample rate, bit depth, and file formats and they all have an overall effect on the quality of conversion. He points out that the decision to use any of these particular formats is mainly based on the particular project at hand.
- [Instructor] As we discussed in chapter one on microphones, we learn that they convert acoustic energy into electrical energy for use with a microphone pre-amp. Analog-to-digital conversion is similar in that it converts the electric energy from the output of the microphone pre-amp into digital data that can be stored onto a hard drive of a computer. Digital-to-analog conversion is the exact opposite process in that it converts the digital data back to the analog format. There are many variables that dictate the quality of the digital signal, some of which are sample rate, bit depth, and file format.
Sample rate is the amount of snapshots or samples taken of the signal. The way that we measure this is in hertz per second. The standard sample rate that is used for CD format is 44.1 kilohertz, or 44,100 samples per second. Common sample rates used in professional studios are 44.1, 48, 88.2, 96, and 192 kilohertz. The higher the sample rate, the more snapshots are taken, which capture a more accurate representation of the original audio.
The downsides to this is higher sample rates generate a much larger file size, and also require more CPU power. Bit depth is a reference to the amount of bits that represent one sample. The standard CD format is 16-bit. It is very common to record a project at a higher sample and bit rate, such as 96 kilohertz 24-bit, so that the degradation of quality when converting down to CD format is minimal. As technology advances, we are actually able to record at 32-bit and higher, which like sample rates will increase in quality but also file size.
There are many audio file formats that exist, but I will go over the ones that are most commonly used in recording studio environments. When working on a project, we are mainly using uncompressed files, which are full resolution recordings. The most common are .WAV and .AIFF. WAV is perhaps the most common format because of the ability to embed metadata into the digital files. AIFF is mostly known for being used on Mac computers. Other than the difference in certain features, the audio quality is identical between the two.
Common compressed formats are MPEG, MP3, FLAC, and Apple Lossless Audio Codec. The reason to create a compressed audio file is for the need to shrink the file size for use on the web, or for a consumer to save space on their hard drive. Generally, these suffer a loss of quality as they have lower sample and bit rates. But FLAC and Apple use a special codec that helps preserve the original source as much as possible, while effectively reducing the file size.
With the price of hard drives drastically dropping, there's becoming much less of a need to shrink the size of the files. There are several companies offering high-resolution audio, allowing the consumer to own 96 kilohertz or above versions of their favorite records. Aside from the above variables, there's also the A-to-D and D-to-A unit itself that has a major effect on how accurate the signal gets converted. Most converters are designed with the goal of being as transparent as possible, but there are other products that are quite the opposite.
There are a large amount of people in the industry that will always prefer the sound of their old tape machines, that agree they will never compete with the convenience attached with working in digital. Companies like Crane Song and Burl Audio have risen to the task of creating such a product that caters to those that want to get some analog color out of their converters.
Throughout the course, Greg shares images, diagrams, and audio examples that can help you grasp how this equipment functions, and why you might want to opt for one piece over another. Greg dives into working with different kinds of microphones and preamps, describes the main types of compressors and equalizers, and shows how an analog-to-digital and digital-to-analog converter works. Plus, he covers analog summing—the process of combining multiple audio channels down to a stereo signal—and analog emulation.
- Dynamic, condenser, and ribbon mics
- Tube mic preamps and solid state mic preamps
- Different types of compressors and equalizers
- Analog-to-digital and digital-to-analog conversion
- Analog summing
- Analog emulation