Quickly calculate dB of amplitude, amplitude of dB on the command line, using bc

dboflin

#!/bin/bash

# Save as "dboflin", create symlink as "linofdb"
# Calculate dB from amplitude, amplitude from dB, using bc.
# 2024-05-12 - Moonbase59
# 2024-05-14 - Moonbase59 - add correct rounding
#
# Note: For AMPLITUDE, the factor is 20,
#       for POWER/ENERGY, the factor is 10!

fun=$(basename $0)  # dboflin or linofdb
val=$1

if [ -z "$1" ] ; then
  >&2 cat <<EOF
Usage:
  $fun [value]
EOF
  exit 1
fi

result=$(bc -l <<EOF
# Define functions for bc
# bc -l sets scale to 20

define pow(a, b) {
  if (scale(b) == 0) {
    return a ^ b;
  }
  return e(b*l(a));
}

# round x to d decimals
define r(x, d) {
  auto r, s;

  if (x < 0) {
    return -r(-x, d)
  }
  r = x + 0.5*10^-d
  s = scale
  scale = d
  r = r/1
  scale = s
  return r
}

# dB of amplitude, rounded to 2 decimals
define dboflin(x) {
  auto result;
  result = 20 * l(x) / l(10);
  return r(result, 2);
}

# amplitude of dB, rounded to 6 decimals
define linofdb(x) {
  auto result;
  result = pow(10, x/20);
  return r(result, 6);
}

# call either dboflin or linofdb, depending on $0
$fun($val)

EOF
)

echo $result

dboflin / linofdb

Save above in as dboflin in some place like ~/bin, /usr/local/bin, etc. (should be in path), chmod +x dboflin, then create a symlink ln -s dboflin linofdb.

You can then quickly calculate dB values from a linear amplitude (0..1), or linear values from a dB value:

Bash script, uses the Linux Basic Calculator bc.