2. Recording, Playing, and Editing
in DAWs
Objectives:
- Define RAM buffereing and describe its use in DAW
operations
- Describe how hard drive performance affects the DAW,
and some common practices to work within a drive's limits
- Compare non-linear recording
to linear recording
- Compare and contrast DAW operations with conventional
record/replay systems
- Differentiate between audio files and audio segments
- Give advantages of non-linear editing
Reading
Chapter 3, Desktop
Audio Technology - Rumsey
The Sound File
- Sound file - an individual audio recording of any length (within limits
of the system)
- Allows for random access
- Allows for non-linear use
- Generally stored on disk (fast access)
- Disk can be considered a sound store
RAM Buffering
- Digital audio needs to be delivered in a linear manner (real-time)
- Disk storage is not suitable for linear transfer
- RAM buffer - an application of RAM to regulate data flow to and from
the drive
Operation
- Data stored on disks in blocks - from 512 to 4K bytes each
- At least one block read or written at a time - 8 to 15 ms
- Time compression = 10ms for 100ms or more of audio
- RAM buffer is a "holding area" for audio - regulates the transfer
of audio data
- Recording - audio is captured in real time, fills buffer - blocks
of data then transferred in a "burst"
- Playback - buffer is qucikly filled from disk, processed at
a steady rate
Results of use
- Eliminates timing irregularities odf data transfer to/from storage device
- There is a delay from input to output of buffer
- Dependant on buffer size
- Buffer may be used for synchronization purposes
- Buffer size may or may not be user-selectable
Disk Drive performance Issues
- Speed of disk is most important for primary digital audio performance
(access time and transfer rate)
- Sustained transfer rate is far more important than the instantaneous (or burst) rate
- Access time can limit the device's tranfer rate
- Buffer will "disguise" the effects of erratic access time
- Some media will have different record (write) and replay (read) times
Allocation Units or Transfer Blocks
- Optimal performance can depend on reducing disk access
- Allocation unit's size defines how much data is stored or transferred at
a time
- Typical size for a computer may be 2K - 4K bytes
- Suitable for smaller files, unruly for large files (like audio)
- If a file is written, regardless of size, an entire block
is used
- Some systems will allow changing the block size - if so, the system
can be optimized
- Larger blocks waste more disk space if small files are written,
but move faster for larger files
- Smaller blocks more space-efficient, but reuire more accesses
for a larger file
Track Usage, Storage Capacity, and Disk Assignment
- Required storage space increases with number of channels and number
of saved files or takes
- Time of song * number of tracks
- Reality, probably less, because of non-recorded intervals
- Note: recorded silence is STILL recorded audio
- More simultaneous tracks = greater required transfer rates
- Transfer rate is increased linearly by number of tracks
- A disk can be pushed to its limit with large projects
- Some systems (many older systems) use multiple disks for multiple audio
channels
- Multiple drives will improve capacity and transfer rates
- Old systems - different tracks might be assigned to different disks
- This system severely limited the movement of audio between
tracks
- Current systems can still take advantage of multiple drives
for large projects
Principles of Audio editing
Advantages of non-linear editing
- Speed and flexibility
- Multiple versions or masters
- Non-destructive editing
Sound files and sound segments
- Sound files vs. sound segments
- Segments point ot all or parts of a file
- Segments define only the desired portion of files
- Multiple segments cna refer to a given file
Edit point handling
- Playlist defines what segment is played and when
- Edit point defines a change in whataudio is played
- Butt joint - direct switch from one segment to another
- Problems with butt joints?
Crossfading
- Playlist defines what segment is played and when
- Edit point defines a change in whataudio is played
- Butt joint - direct switch from one segment to another
- Problems with butt joints?