DAW Recording
ADCs and DACs
ADC - Analogue-to-Digital Converter
DAC - Digital-to-Analogue Converter
Low-end units are often combined ADC/DAC interfaces, potentially with a built-in pre-amp too.
Mid Range - High-end units are usually standalone hardware, specialised and focused.
High-end units are typically outboards, superior in design and quality.
(Tip: Ultimately the quality of a signal is only as high as that which the weakest link in a signal path can afford i.e. the benefits of a chain of high end equipment will not be perceivable if the signal is ultimate converted by a cheap ADC/DAC.)
Latency
Latency should by default be kept to the absolute minimum where possible.
Acceptably low latency may be a delay of 3ms or lower.
Anything beyond 6ms is bordering futile.
Latency should be set as low as possible, but comfortable clear the point of byte dropping.
Audio Interfaces such as ADC/DACs generally use 'input buffers' to set the rate of latency.
One should avoid using any processing beyond the necessary when recording as this will only drain valuable CPU and cause hangups/dropouts, the result will be better quality audio and more tightly synced monitoring.
Some AIs may employ zero-latency monitoring, channeling a direct loop from input to output, producing accurate monitoring alongside backing track playback for timely recording.
In the absence of Z-L monitoring -
- A similar result can be achieved by connecting the interface input to an aux, bus or direct output on the A or D console to avoid recording the entire temp mix to the new track. With digital consoles there will be some latency experiences, but often only around the 2ms or less mark due to the optimised OS installed.
TO AVOID LATENCY -
- LOWER INPUT BUFFER SIZE
- USE Z-L MONITORING
- USE AN OUTBOARD CONSOLE
- AVOID THE USE OF PLUGINS
Firewire vs USB
USB 2.0 - 480kbps data transfer rate - utilises as MASTER/SLAVE configuration
- Adds system overheads, resulting in slower data flow between devises.
- May cause dropouts when recording multiple tracks
FireWire - 400kbps data transfer rate - utilises PEER to PEER configuration
- optimal path for data transfer established via communication between devices.
- superior choice for multiple track recording
Interface Card
- Very high track counts (8+) will require an IC to plug in directly to the computers PCI (peripheral component interconnect) bus.
- Pro Tools|HD utilises an IC for this purpose
Headroom and Gain Staging
Gain Staging
- Proper setting of gain at each stage of a signal path, to prevent overloads occurring at any point.
Example - Analogue Console
Input gain > EQ > Pan Amplifier > Fader buffer > Bus > Master Bus
All of these stages are points at which overload may occur, and where care should be taken to set gain properly.
Pre-fader and after-fader listen is for monitoring for overloads at different points along the signal path.
(PFL & AFL)
Channel Faders
- The level of the channel faders should always remain below the level of the subgroup and/or master faders.
- This is especially crucial for those channels with high gain structures: utilising highly active EQs and/or plugins providing additional gain.
LEAVE HEADROOM! - Generally 10Db HR, at least 6-3DB.
Headroom
A legacy of early 16 bit digital recording is a belief that a protocol of mixing as close to 0Db full scale, using all available bits, is needed for maximum resolution and to avoid noise produced by unused headroom.
While this was somewhat necessary for early 16 bit digital recording, the 24 bit DR of today and intrinsic calculation of coefficients mean that this is simply no longer the case, and it is wise to leave healthy headroom to preserve transients, avoiding clipping, and produce a cleaner, more harmonious mix.
The super-fast transients produced by the initial attack of an instrument can peak as high as 20Db, while a VU meter may read 0Db. (Peak meters are far more accurate.)
Recording too hot (approaching or meeting 0Db FS) will likely result in overloading and tonal transients being clipped, produce a dull and less than realistic sound.
Headroom Summary
- Keep all ch. faders below subgroup and master faders
- Channels with high gain structures should be lowered, rather than raising all other channels to the same level.
- Leave headroom - you can raise the level later in the mixing process.
Tips from Gannon Kashiwa of Digidesign
Causes of decreased fidelity -
- overcompressing
- too much processing to achieve a 'CD sound' too early in the process
- maxed out mixes with master chains allowing little room to work for mastering studios
Headroom -
- Recommends 3-6Db
- Issues with reaching 0Db FS include potential for inter-sample clipping, i.e. if two samples breach in to overload, an overage will be assumed and compensated for during the reconstruction of the waveform, meaning clipping applied to peaks will carry over and result in a clipped waveform even between breaches (ms) - this the reconstruction filter at work
Mixing
- mix in groups
- distribute EQ and compression across a number of stages, do not over work any one instance of either for a cleaner result.
Filtering
- Use low pass filters to cut out the unnecessary highs of sounds to avoid competition for the desired highs of other sounds.
24 bit DAWs
- calculate vol and pan coefficients as 24 bit coefficients, meaning level no longer has sonic or mathematical consequence, unlike 16 bit predecessors.
(Unity Gain = Input 0Db + Output 0 Db)
GOOD ANALOGUE PRACTICE TRANSLATES TO DIGITAL REC. PRACTICE LOGICALLY
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