Fast Cochlea Transform™
The cochlea is the most complex part of the ear and central to the human auditory system. It is responsible for transforming sound pressure waves into electrical information that the brain can interpret as a sound. Audience’s proprietary “Fast Cochlea Transform™” (FCT) performs a similar transformation function within the voice processor, converting a time domain representation of sound into a frequency domain representation.
Sound captured by the microphones is sent to the voice processor and digitized before entering the FCT. Operating like the human cochlea, the FCT separates the sound into its frequency components to map the digital audio stream in a three-dimensional, high-quality spectral representation of the sound mixture. The ability to transform sound into a spectral domain is what enables the characteristics or cues in the digital audio stream to be separately identified as different sound sources. This is particularly important to manage simultaneous sounds, allowing these to be uniquely evaluated and grouped by source using the principles of CASA.
The FCT is similar to the “Fast Fourier Transform” (FFT) that is commonly used in digital signal processing. Both transform the signal into the frequency domain for audio processing, but the FCT is better able to map audio signals in several critical ways:
- Log-Frequency Scale: The FFT transforms the audio signal into the frequency domain on a linear scale, while the FCT performs its transformation on a logarithmic-frequency scale. A log-frequency scale improves the efficiency of the transformation by putting the resolution and computational resources where the listener can hear it.
- Direct Computation of Critical Bandwidths: The uniform bandwidth of the FFT contrasts with the well-known Critical Bandwidths of the human ear. The FCT computes its spectral transformation with the Critical Bandwidths built directly into the computation.
- Optimal Time-Frequency Tradeoff: The FCT provides greater accuracy in representing the audio signal at both low and high frequencies. At low frequencies, the FCT provides greater spectral resolution, which allows the detection of harmonics and recreation of sound more accurately. At high frequencies, the FCT provides a faster response rate, which captures dynamic changes more accurately.
- Continuous Signal Processing: The FFT transforms the audio signal by reading blocks or frames of data that are taken at a particular frame rate. When the audio signal spans these data frames, spurious artifacts can be introduced and wreak havoc with the audio stream by introducing extra "noise" into the signal. This "noise" can take the form of additional audio signals at additional frequencies, as well as inaccurate frequency representation of the real signal. The FCT takes a completely different approach. Instead of operating on blocks of data, the FCT continuously streams the incoming signal into the transformation. The result is that it can transform the audio signal into its appropriate representation without introducing frame artifacts, or additional "noise" that would have to be removed from the system.
The audio signals now move through a series of functions for processing and interpreting sounds within the CASA system, to produce clear voice communication and suppress background or ambient sounds.