DIGITAL AUDIO WORKSTATIONS (D.A.W.s) Avid Pro Tools is one of many digital audio workstations available today and will be the D.A.W. that we focus on during the course of this class. Though we will be focusing on Pro Tools, many of the concepts learned in this class will apply to other D.A.W.s as well. There are two types of recording mediums: ! Linear recording mediums generally make use of analog or digital tape. You must use transport functions (play, stop, rewind, fast forward) to navigate around the audio. Edits are performed by cutting/splicing or overdubbing. Linear systems are destructive in nature, meaning that alterations to the signal on tape cannot be undone once performed. ! Nonlinear recording mediums generally make use of disk storage mediums. Nonlinear recordings allow immediate navigation and altering of any point in the audio without the need to make use of transport functions. Nonlinear systems are non- destructive in nature. Pro Tools and other D.A.W.s are nonlinear systems. DIGITAL AUDIO BASICS All captured sound is initially analog, meaning that a transducer has converted physical sound waves into a continuous electrical signal. Converting analog signals to binary code – the computer language of 0s and 1s - creates digital audio files. The resulting digital file can then be played back and manipulated in the D.A.W.. Analog signals are converted to digital information using a device known as an analog to digital converter (A.D.C.). An analog to digital converter repeatedly samples the incoming audio at a set sample rate and bit resolution (think of a camera taking thousands of still pictures per second to create the illusion of movement) and stores the resulting information as a digital audio file. An Apogee AD16x analog to digital converter and a DA16x digital to analog converter SAMPLE RATE Sample Rate in digital audio refers to the number of samples of audio taken during a unit of time, expressed in Hz (hertz). The standard sample rate for an audio CD is 44.1kHz (44.1 kilohertz, or 44,100 hertz). Sample rate is instrumental in determining the frequency content of an audio signal. The Nyquist sampling theorem states that the sample rate must be twice as high as the highest frequency to be reproduced. For example, to reproduce frequencies up to 22,500 Hz, the sample rate must be at least 44,100 Hz. As the ideal human range of hearing is (on average) approximately 20Hz - 20,000 Hz, sample rates of 40Hz or above are required to accurately reproduce sounds as we hear them. Higher sample rates more closely approximate the original signal and retain more frequency information, but also require more processing power and disk space to work with and store. For example, recording audio at a sample rate of 88.2 kHz will use twice as much processing power and disk space as a recording made with a sample rate of 44.1 kHz. BIT DEPTH Bit Depth refers to the number of bits (binary digits) of information stored in each audio sample. Bit depth is instrumental in determining the signal’s dynamic range and signal-to-noise ratio. Higher bit depths retain more digital information about the sampled audio. For each 1-bit increase in bit depth, the signals dynamic range will increase by 6dB – so a 16-bit recording has 96dB of dynamic range, and a 24-bit recording has 144dB of dynamic range. The range of human hearing is roughly 140dB. This extra dynamic range allows the user to record at lower levels without audible noise, leaving more headroom and less change of digital clipping. You can see here that a higher bit depth more accurately reproduces the original signal. Once the analog audio has passed through the A.D.C. and has been converted to digital files, these files are stored on a hard disk and can be played, manipulated, etc. in a nonlinear fashion. 32-BIT FLOATING POINT FILES Pro Tools (and other DAWS) now allow the use of 32 bit floating-point files. It’s worth pointing out that these files are sonically identical to their 24-bit counterparts, but the additional encoded data gives them a much higher theoretical dynamic range and lower noise floor. The advantage is that using the 32-bit floating-point format will allow improved signal processing of the audio in question with less chance for clipping, noise, and other digital artifacts. SO NOW WHAT? In order to be able to hear the resulting digital audio, the information must be converted back to analog in order to be reproduced by the speaker. A digital-to-analog converter (D.A.C.) is used to convert digital information to electric voltage so that it can be reproduced on real world playback systems. TO SUMMARIZE: Analog signal input (Microphone, Instrument, etc.) ⇓ Converted to digital information using analog to digital converter ⇓ Digital information is played back / recorded / manipulated / mixed in D.A.W. Digital information output from D.A.W. ⇓ Digital information converted back to analog signal via digital to analog converter ⇓ Analog signal is reproduced by speakers / headphones / etc. INTERFACES The generic term “interface” refers to a device used to connect audio devices (microphones, preamps, speakers, mixing consoles, etc.) to a computer, tablet, or other digital recording device. Interfaces are available in a huge variety of configurations. Most offer a combination of analog-to- digital and digital to analog converters, and many offer additional features such as mic preamps, headphone connections, on-board DSP processing, and monitor management. Interfaces are generally connected to the host computer via USB, Firewire, Thunderbolt, or PCI connections. Since interfaces scale from very simple to very extensive, the user has the freedom to choose an interface that offers the features that suit his or her needs. The Universal Audio Apollo interface COMMON PRO TOOLS DIGITAL AUDIO FILE TYPES (FROM THE PRO TOOLS REFERENCE GUIDE) .WAV (Broadcast wave format) This was the native format for older Windows- based Pro Tools systems, but is now supported on Windows and Mac. To use a BWF (.WAV) file in Pro Tools, you can drag and drop from the DigiBase browser, Windows Explorer or Mac Finder, or a folder, or you can use the Import Audio command. Files in this format do not have to be converted to be used in Pro Tools. .AIFF (Audio Interchange File Format) Similar to .WAV - To use an AIFF file in Pro Tools, you can drag and drop from the DigiBase browser, Windows Explorer or Mac Finder, or you can use the Import Audio command. Files in this format do not have to be converted to be used in Pro Tools. 16-bit, 44.1 kHz .WAV is the standard CD audio file format. It is recommended to use at least 24- bit, 44.1 kHz .WAV or. AIFF for audio recording and mixing. MP3 and other compressed formats are not recommended. DSP-BASED AVID PRO TOOLS SYSTEMS Pro Tools HD and HD-X systems are DSP-based systems, meaning they use dedicated DSP chips for processing power, which frees up the host computer for other tasks and provides improved stability and low latency, especially when working with large sessions. Pro Tools HD systems consist of Pro Tools HD software, at least one PCI/PCI Express DSP card and at least one compatible interface. The cards provide DSP power for plug-ins and mixing/routing, and connections for I/O. Pro Tools HD systems can also utilize native processing power from the host computer for certain tasks. Modern DSP-based systems run AAX (v.10 and up) as well as RTAS and Audiosuite (v.10 and earlier) plug-ins. NATIVE AVID PRO TOOLS SYSTEMS Avid also offers several native Pro Tools systems. The term “native” means that the host computer provides processing power for the system. As computers become more and more powerful, native systems have become increasingly viable for use in professional audio. Pro Tools HD|Native systems consist of Pro Tools HD software, a Pro Tools HD|Native card or hardware device, and at least one compatible interface. These systems provide similar functionality to DSP-based systems except there is no onboard DSP processing – all processing is done natively (using the host computer’s processing power). They run AAX (v.10 and up) as well as RTAS and Audiosuite (v.10 and earlier) plug-ins. Pro Tools (V.9 and up) – Starting in software version 9, many of PRO TOOLS HD’s features have been integrated into PRO TOOLS LE, and the software is now simply called Pro Tools. Modern Pro Tools systems are compatible with almost any modern audio interface, including those by third-party companies, and they can also be run without an interface attached. NATIVE AVID PRO TOOLS SYSTEMS (continued) Pro Tools systems run AAX plug-ins (v.10 and up), as well as RTAS, and Audiosuite plug-ins (v. 10 and earlier). Pro Tools Express – A feature-limited version of Pro Tools that is bundled with some Avid interfaces. Pro Tools | First – A free, feature-limited version of Pro Tools that will be available for download online in early 2015. An Avid Pro Tools HDX system – from top to bottom – Pro Tools HD software, HD I/O interface, and HDX PCIE card. SETTING UP AND TROUBLESHOOTING YOUR MAC FOR PRO TOOLS Since multiple classes and students use the computers in the D.A.W. lab, and the computers are “wiped” after every semester, some settings commonly get changed in the Mac operating system that cause complications with the functionality in Pro Tools.