Sound Devices 722 - Manual (Page 21)

722 User Guide and Technical Information
19
Sampling Rate and Bit Depth
When recording the 722 generates uncompressed PCM audio WAV files in the Broadcast Wave File
format at the user-selected sampling rate and bit depth. The 722 LCD calculates available recording
time based on the sampling rate, bit depth, number of tracks set for recording and the selected stor-
age media available capacity. See the Calculating Recording Time later in this guide to estimate record
time.
Sampling Rate
When a sampling rate is selected for recording, all tracks are recorded at the selected sampling
rate. Sampling rates are selected among common rates from 32 kHz to 192 kHz. Additionally,
non-standard sampling rates can be applied when the 722 is word clocked from an external source
(clock sources between 32 kHz and 192 kHz). When recording off-speed sampling rates files will be
stamped with the rate closest to an internally generated frequency.
Relationship Between Sampling Frequency and Audio Bandwidth
The sampling frequency is expressed in samples per second (in hertz) and defines the number of
times in a second that the analog audio signal has been measured. Sampling frequency determines
the audio bandwidth, or frequency response, that can be represented by the digital signal. A quick
estimate of the maximum bandwidth capable of being represented at a given sampling rate is maxi-
mum analog frequency = sampling frequency/2. Higher sampling frequencies allow for wider audio
bandwidth.
The 722 generates the following sampling rates:
• 32 kHz
• 44.1 kHz
• 47.952 kHz
• 47.952kF - file stamped at 48 kHz
• 48 kHz
• 48.048 kHz
• 48.048kF -file stamped at 48 kHz
• 88.2 kHz
• 96 kHz
• 96.096 kHz
• 96.096kF - file stamped at 96 kHz
• 176.4 kHz
• 192 kHz
Bit Depths
The 722 records at bit depths of either 16 or 24 bit. 24 bit recording provides greater dynamic range
and addition headroom for signal peaks relative to 16 bit recordings. 24 bit recording (versus 16 bit)
is a significant benefit for field production audio tracks.
Bit Depth = Available Dynamic Range
Bit depth defines the digital “word length” used to represent a given sample. Bit depth correlates to
the maximum dynamic range that can be represented by the digital signal. Larger bit depths accom-
modate more dynamic range. A quick estimate of maximum dynamic range capable of being rep-
resented by a given word length is dynamic range ~= no. of bits x 6 dB. Bit depth is an exponential
measure (exponent of 2), so as bit depth increases, the amount of data it represents increases expo-
nentially. The majority of field recording is done with 16-bit audio, therefore, each sample is rep-
resented by a digital word of 2^16 (65,536) possible values. 24-bit audio has a word length of 2^24
(16.7 million) possible values per sample.