Huron & SNAP Documentation

Fixed Point Digital Audio Data Representation
Data Formats and Scaling
Considerations
Digital audio data within the Huron system is transferred over
the Huron bus in 24-bit twos-complement format. This data
format provides for representation of audio data with Root-
Mean-Square (RMS) quantisation at a level of 146.3dB below
the RMS level of a full-scale sine wave. The range of 24-bit
values is as follows:
Hexadecimal
value
Decimal value Signal Level Description
0x7FFFFF 8388607 0.99999988 Positive full scale
→ → → →
0x000001 1 0.00000012 Smallest positive value
0x000000 0 0.00000000 Zero level
0xFFFFFF -1 -0.00000012 Smallest negative value
→ → → →
0x800000 -8388608 -1.00000000 Negative full scale
Finite Impulse Response Filter (FIR) Coefficient Scaling
Filter Scaling for Unity Gain
To gain optimum performance from the system, the following
files must be scaled appropriately:
• FIR filter coefficients which are loaded into the Huron
system via *.SIM data files. The data in these files is stored
as 24—bit fixed point data.
• Time domain impulse response filters used by the Huron
Convolver tool.
If necessary, *.SIM files can be re-scaled using the SIMWIN
utility MultVec or SimScale.
There are two important factors to consider during the
generation or re-scaling of data files:
FIR filter coefficient files should ideally be scaled so that the
audio data that is used in typical listening tests will pass through
the FIR filter with approximately unity gain. Coefficient files
that are scaled up too high will result in a filter which boosts the
output level, possibly resulting in clipping at the FIR filter
output when the input signal is close to full scale. Coefficient
HURON TECHNICAL MANUAL PAGE 291