Real World Advantages of 24-Bit Recording
24 bit /192 kHz sampling looks impressive as a specification. Manufacturers offer these “marketing specs” for consumers to gobble up. In practice, the analog circuitry ahead of the conversion and storage system is the defining factor of a digital system’s performance. The fact that a device is 24 bit doesn’t have much to do with its audio performance. Leaving this fact aside, let’s look at what 24 bit recording can do in real world environments with high
performance gear… 24 bit resolution versus 16 bit resolution is
a genuine advantage. 24 bit recording allows the sound engineer to use far more of the working range of a system than 16 bit systems ever could. In 16 bit environments maximizing the signal level into the A/D conversion stage is important to suppress system noise (yes, there is noise with digital…) In high-quality 24 bit conversion systems getting analog signals as close to 0 dBFS is far less critical from a noise perspective than with 16 bit. While best practice dictates using all of a systems dynamic range, when levels are set incorrectly the 24 bit system is far more accommodating than 16 bit.
As an audible example, six unique speech tracks were recorded to demonstrate the effect of different record bit depths on their noise floor. At each bit depth (24 bit, 16 bit with dither, 16 bit without dither) two recordings were made, one at a full signal level and one intentionally recorded 40 dB down. The tracks recorded at typical level settings had full meter deflection, while the tracks recorded 40 dB down barely registered on the lowest meter LEDs.The recordings below were made with the following equipment and parameters:
one Shure KSM44 microphone, its self-noise specification is extremely low,
Belden 1800F 110 ohm microphone cable (as if this matters…)
three 744T digital recorders, the recorders at 16 bit were fed from the digital output of the 744T at 24 bit
gain settings for the typical tracks were with ~40 dB of gain applied to the microphone input
the gain settings for the attenuated tracks were at LINE level on the 744T
All of the recorded tracks were then normalized so their playback levels would be identical. This essentially raised the digital gain of the under-recorded tracks by 40 dB. The files were then converted to MP3 format for web delivery using the Sony MP3 encoder from within
Sound Forge. A direct comparison from track to track can now be made.24 Bit Recordings
24 bit with a full signal level, not right at 0 but close (128 kbs mono MP3)
24 bit with the signal 40 dB down (128 kbs mono MP3)
16 Bit Recordings – with Dither
16 bit with dither with a full signal level, not right at 0 but close (128 kbs mono MP3)
16 bit with dither with the signal 40 dB down (128 kbs mono MP3)
16 Bit Recordings – without Dither
16 bit without dither with a full signal level, not right at 0 but close (128 kbs mono MP3)
16 bit without dither with the signal 40 dB down (128 kbs mono MP3)
What you hear is that the tracks recorded at full signal level sound largely identical, whether recorded at 24 bit or 16 bit. However, the tracks recorded 40 dB down are very different. Most important is how usable the low level 24 bit signal is after normalization. It is definitely noisier than the full gain recording but it held up quite well. The 16 bit recordings highlight how important recording full scale digital is in a 16 bit environment.
