Eilex HD Remaster

Hi-Res Audio Real-Time Remastering

  • 88.2/96/176.4/192 KHz
  • 24/32 Bit
  • Ultra-High Performance Even-Order Multiple-Harmonics Generator
  • Real-Time Operation
  • Extremely Small Computation Requirement
  • For All Hi-Res Products

Eilex HD Remaster converts up-sampled (88.2/96/176.4/192 KHz) audio sources to Hi-Res audio in real-time. It works on radios and TVs as well as CD and DVD materials.

Conventional Hi-Res processes simply up-sample the source and place the new sample points on the predicted curve. That does not contribute any sound improvement. Increased resolution is often filled with random noise instead of meaningful data.

Eilex HD Remaster generates multiple even-order harmonics from the audio source, filling the data up to the theoretical frequency limit. Its Dynamic Bit-Allocation helps to fill the newly added bits with meaningful data when the bit depth is increased to 24 or 32 bits.

The Hi-Res materials created by Eilex HD Remaster add detail, warmth, smoothness and nuance to the sound.

Eilex HD Remaster operates in the time-domain and its computational requirement is extremely small. This is a big advantage for battery powered devices including Portable Hi-Res headphone players.

Note:

  1. Eilex HD Remaster has greatest efficiency with Eilex SRC (Sampling Rate Converter). [Note: SRC employment depends on target hardware architecture.]
  2. Eilex Harmony or Eilex Focus is recommended to improve compressed “lossy” audio sources such as MP3 and AAC before processing with Eilex HD Remaster.

Frequency Range Expansion of CD

Fig 1 shows the procedure of Eilex HD Remaster using an example of CD up-conversion.

CD audio is sampled at 44.1 KHz and has a bandwidth of 22.05 KHz. If it is over-sampled at 176.4 KHz (4×), the bandwidth extends to 88.2 KHz. However, there is still no data from 22.05 KHz up to 88.2 KHz.

To fill the empty space between 22.05 KHz and 88.2 KHz we need meaningful data. Naturally, no fundamentals are found in this region, but mostly harmonics. If we fill the space with the harmonics generated from the information below 22.05 KHz, we can accomplish our task. Eilex HD Remaster uses a proprietary even-order multiple-harmonics generator (generates even-order harmonics exceeding the 70th order) to fill the space up to 88.2 KHz (in the case of 176.4 KHz up-sampling).

Fig. 1  Hi-Res Conversion of CD (Frequency Range Expansion)
Fig. 1 Hi-Res Conversion of CD (Frequency Range Expansion)
Fig. 2  CD Up-Sampled at 176.4KHz
Fig. 2 CD Up-Sampled at 176.4KHz
Fig. 3  CD Up-Sampled at 176.4KHz
Fig. 3 CD Up-Sampled at 176.4KHz

Fig. 2 is a spectral frequency display (H: Time, V: Frequency) of a CD after up-sampling at 176.4 KHz. There is no information above 22.05 KHz. Fig. 3 shows the frequency analysis (H: Frequency, V: Magnitude) at the time indicated by the cursor (white vertical line) in Fig. 2. No signal is seen over 22.05KHz.

Fig. 4  HD Remaster Applied
Fig. 4 HD Remaster Applied
Fig. 5  HD Remaster Applied
Fig. 5 HD Remaster Applied

Fig. 4 is the result of Eilex HD Remaster processing. The information over 22.05KHz is properly generated. This is observed in Fig. 5 displaying a smooth decay in the high-end frequencies, as true Hi-Res recordings exhibit.

An example of true Hi-Res recordings (Mozart, Violin Concerto No. 4, The Nordic Sound, 96 KHz 24-bit Blu-Ray) is shown in Fig. 6 and 7.

Fig. 6  True 96KHz 24-bit Hi-Res Recording
Fig. 6 True 96KHz 24-bit Hi-Res Recording
Fig. 7  True 96KHz 24-bit Hi-Res Recording
Fig. 7 True 96KHz 24-bit Hi-Res Recording

The key mechanism of Eilex HD Remaster is a high-performance even-order multiple-harmonics generator. Fig. 8 displays its actual operation. From a 1 KHz fundamental signal, even-order multiple-harmonics exceeding the 70th order are generated in the specified amplitudes.

This process is performed in the time-domain to minimize the computation resources and realize real-time operation.

Fig. 8  Even-Order Multiple-Harmonics Generator
Fig. 8 Even-Order Multiple-Harmonics Generator

Dynamic Bit-Allocation

At time of up-sampling, the bit depth can be increased from 16bit to 24bit (or 32bit). HD-Remaster allocates meaningful values to the newly generated lower bits.

Fig. 9 is part of a CD recording. Vertical and horizontal axes are amplitude and time, respectively. The black dots are 44.1 KHz 16-bit sample points. (To be exact, the waveform should be shown in steps. But, because the waveform after low-pass filtering becomes smoother a curve is used here instead.)

Fig. 9  A Part of CD Waveform
Fig. 9 A Part of CD Waveform
Fig. 10  CD Waveform after 4X Over-Sampling
Fig. 10 CD Waveform after 4X Over-Sampling

By over-sampling the audio data of a CD, we can improve the temporal precision. The white dots in Fig. 10 are newly created sample points after over-sampling to 176.4 KHz (4×). That expands the 22.05 KHz bandwidth to 88.2 KHz, but the audio information remains unchanged and the space between 22.05 KHz and 88.2 KHz is empty. The newly generated sample points are placed on an expected waveform by calculation. The waveform is exactly the same after low-pass filtered and no sound improvement is expected.

Fig. 11  Conventional and Eilex Dynamic Bit-Allocation
Fig. 11 Conventional and Eilex Dynamic Bit-Allocation

Fig. 11 illustrates the behavior of conventional versus Eilex Dynamic Bit-Allocation. The conventional bit-allocation cannot move the original CD’s sample points and the new sample points have limited range of placement. HD Remaster’s Dynamic Bit-Allocation places both the CD’s sample points and the new sample points in real-time without any restrictions or limitations.

Fig. 12 HD Remaster Wave Form
Fig. 12 HD Remaster Wave Form

Fig. 12 shows the result of Dynamic Bit-Allocation. The output of the even-order multiple-harmonics generator fills the space between 22.05 KHz and 88.2 KHz. The newly obtained information decides the value of each sample point and determines its location on the curve. When the harmonics are added the waveform changes its shape. (Compare Fig. 12 with Fig. 10)

Both the original CD’s and the new sample points move to the new locations. The new waveform should be similar to the original waveform, before CD format degraded it. Thus, the CD sound improves.

When the bit depth is increased from 16-bit to 24- or 32-bit, HD Remaster fills the new lower bits with meaningful information rather than random noise. This improves the sound as well.

Not limited to CD, Eilex HD Remaster works on all audio materials including DVD, TV and radio.

Realizing Eilex HD Remaster

  1. Solution: Firmware. Process size is about 16/32 MIPS (@96/192KHz)
  2. Location: Up-converted PCM Line Level

Eilex Harmony and Eilex Focus

When up-converting digitally compressed audio materials like MP3 or AAC, Eilex Harmony or Eilex Focus (both in-band harmonics generators) are used before using Eilex HD Remaster for further sound improvement. The majority of discarded information in the lossy digital compression is weak signals around the adjacent stronger signals. Such weak signals are mostly harmonics which relate to the sound quality. These pre-processes effectively regenerate the lost harmonics from the fundamentals in the MP3 or AAC, recovering the sound quality.

Eilex Harmony generates both even- and odd-order harmonics, working on the full-range of the audio signal. On the other hand, Eilex Focus generates only 2nd order harmonics and applies to a specific frequency range, giving bolder sound enhancements. (Ref. Tech notes for Eilex Harmony and Eilex Focus.)