|Persona Digital |
Music Studio Technology
Digital audio workstation (DAW) refers to a variety of hardware and software combinations that create a virtual studio, including an audio multitrack mixer and recorder, MIDI recording and playback, usually incorporated in a host computer with audio/midi interface hardware. A professional DAW must have high quality ADC-DAC hardware, professional audio software and a fully empowered midi sequencer. Home studio versions of DAWs are increasingly common and affordable but have limited capabilities. To be really useful, the computer host needs a fast multicore CPU, > 8 GB RAM and 2 fast SATA hard drives > 1000 GB. 2 drives are required: the boot drive should contain the operating system, programs and data; a second drive should be committed to audio recording.
Brief History of Audio Recording
Thomas Edison invented the phonograph in 1877. His recording medium was cylinder covered with wax that was etched by a stylus that turned sound into grooves. Playback was a reverse process using mechanical means of amplification. These phonograph cylinders could not be produced in quantity. A more successful medium, the flat disc, recorded a mechanical analogue of sound waves horizontally across the width of the track. The horizontal disc rotated on a record player and a movable arm guided a pickup needle along the tracks. The disc became the standard recording medium for several decades.
Electronic amplification appeared in the 1930s and permitted progressive improvements in recording and playback equipment. I recall being impressed by the new, expensive hi-fi amplifiers and speakers that appeared in the 1950’s in monophonic form. New turntable designs featured magnetic cartridge pickups that that floated through the grooves on vinyl discs described as long play albums. The disc approach continues in the form of CDs and DVDs that contain digital data. Sound is processed thru analogue to digital converters to write digital bytes on hard drives and portable media. Players convert digital data to analogue signals that drive speakers to reproduce sound.
Recording studios are moving toward computers and software mixers. Desktop computers with fast dual to quad core processors, gigabyte RAM chips and SATA hard drives are now common and inexpensive. With the right software, they can do multitrack audio mixing and editing as well as professional equipment. Old obstacles to computer based recording have disappeared.
Audio Processing Components
Compressor A compressor automatically controls the volume of an audio signal. Its main function is to avoid transients that exceed tolerances of the recording system and cause clipping. You set a threshold level and tell the compressor how quickly to react and it limits the volume. In a digital mixer 0dB is maximum before clipping occurs and recording peaks are best kept below -1dB. Compression can begin at -20dB. The compressor's negative gain is determined as a ratio. A ratio of 5:1 will reduce the input signal (5) to an output of 1dB over the threshold. When the sound volume falls below the threshold level, the gain returns to normal. The attack time determines how long the compressor takes to reduce the gain. The release time determines how long the gain takes to return to normal after the input signal has fallen back below the threshold.
While a compressor may be a useful audio processors, its proper use requires technical knowledge, experience and good judgment. Final decisions are made by listening and not technical preconceptions. Recording performances through a microphone may require some compression at the source. Vocal recordings tend to be the most demanding unless the singer is a real pro. In the studio, capacitor microphones are used for vocals. Place the mic about nine inches from the singer’s mouth and use a pop shield. Vocal compression should be minimal - just avoid clipping- up front to avoid losing dynamics that cannot be restored later. Careful mixing with faders set properly and volume envelops on each track acts as a deliberate, controlled form of compression. reserve compressors for the mastering stage when each composition must fit into the meta-composition of an album. I use a volume ceiling of -1.2dB for competed recordings and try to achieve that with minimal compression.
Noise Gate Recording with microphones is difficult. Background noise can be a big problem and noise gates offer a solution. The idea is that the sounds of interest are louder than background noise -- you set the gate to block low level signals and open with louder signals. The noise floor threshold can be set around -10 to 30db and the opening rate of about 1 second "fades out" the audio signal as the gate come on -- this prevents the gate from chopping off the tails of meaningful sounds.
Reverb creates the illusion of space, but interferes with stereo localization. To maintain stereo placement, use a mono reverb panned to the same position as the original dry sound. Reverb can make vocals better but tends to push the vocals back in the mix when they should be up front. Pre-delay values of 60-100 milliseconds and early reflections reinforce the dry sound. Avoid reverb on bass sounds. Use a short ambience program or a gated reverb to add space to a kick drum.
Equalization is often used to fix sound that was not correct at the source. Reducing the frequencies that are too prominent is better than boosting the weaker ones. Sounds that are pleasing alone may not sit well in a mix. The fix is sometimes to use high- and/or low-pass filters to restrict spectral content. Low frequencies, 200-400HZ, are produced by many instruments and may be selectively filtered to avoid mix mud.
Dry mix until you are pleased before you add any effects or signal processing. Effects are best used a finishing touches. Vocals with pitch problem can be fixed with pitch-correction processors. Enhancers are best used on specific sounds in a mix to make them stand out. Use the enhance in a separate bus and send only the selected sounds that need enhancing. Adapted from Paul White’s Tips, Sound On Sound, July 1999
Staying Dry: Effects (wet) are added to an original sound (dry) creating a dry/wet ratio. My goal is to create dry mixes that are very good without any compression, equalization or reverb. Recordings using electronic keyboards and synths have many options for sound crafting without using effects later in audio production.