TLV320AIC3254: Convert integer to coefficient data format

Hi, Rob,

I am posting the content of the post you mention below.

Converting from linear or dB values into hex values

Applies to:

• AIC3254-like devices (24-bit C-RAM)
• AIC3111-like devices (16-bit C-RAM)
• TASxxxx miniDSP devices (24-bit C-RAM)

To convert from a dB or linear value into a format the device understands it is necessary to understand the data format of the device. The miniDSP devices store user-accessible variables in Coefficient Memory (C-RAM). The bit width of C-RAM may be different from device to device as shown above.

As an example, the volume control volume level is determined by the value stored its C-RAM location. A 0dB volume level (1x gain) corresponds to 0x400000 (24-bit device) or 0x4000 (16-bit device). This means that the volume control assumes a 2.xx format, where the MSB is the sign bit, the MSB-1 is a magnitude bit and xx are the fractional bits. This is a 2's complement format, meaning that numbers will range [0x800000, 0x7FFFFF], where 0x80... is the most negative number and 0x7F...is the most positive number. Some examples:

• 1.xx format: [-1, 0.999...], max 0 dB
• 2.xx format: [-2, 1.999...], max 6dB
• 3.xx format: [-4, 3.999...], max 12dB
• 4.xx format: [-8, 7.999...], max 18dB

In general, a number can be converted from decimal to a M.xx format hex value as follows:

Value_HEX = DEC2HEX(Value_DEC x 2^N-M), where N is the bit resolution of the memory location.

 If the value is provided in decibels (dB), it can be converted as follows:

Value_HEX = DEC2HEX(10^Value(dB)/20 x 2^N-M)

Note that values greater than 2^N-1-1 and less than -2^N-1 are out of bounds if converting to hex.

As an example, for the volume control found in PurePath Studio (2.xx format), a gain of 0dB will result in:

Value_HEX = DEC2HEX(10^0/20 x 2^24-2) = 0x400000

The table below shows additional values.

  Example Volume Control Values in Hex

To convert from hexadecimal back to decimal:

Value_DEC = HEX2DEC(Value_HEX) / 2^N-M

To convert a decimal value back to dB:

Value_dB = 20 x log₁₀(Value_DEC)

As an example, 0x400000 (as a 2.xx hexadecimal number) can be converted to linear as follows:

 Value_DEC = HEX2DEC(400000) / 2^24-2 = 1

The dB / Linear to Hexadecimal calculator can be downloaded below:

0523.dB_Linear_to_Hex.xlsx

Best Regards,

  -Diego Meléndez López
   Audio Applications Engineer