ここから本文です

Enchanting Instruments 99 - U-he SATIN Tape Emulator with dbx Noise Reduction

2024-12-25

Theme:sound&person, sound

This time, we will explain dbx noise reduction (NR). SATIN includes both dbx I and dbx II, but it seems the original name could not be used directly, so it has been replaced with the name "uhx."
dbx is the name of an audio company founded in 1971 by engineer David Blackmar. Upon its establishment, the company began its business in noise reduction. In addition to NR, products like the dbx 160 compressor are also well-known. Currently, dbx operates under Harman International, a subsidiary of Samsung Electronics.

  • uhx Type I = dbx I (Professional use, introduced in 1971)
  • uhx Type II = dbx II (Consumer use, primarily for cassette tapes, introduced in 1981)

How dbx Noise Reduction Works

The dbx noise reduction (NR) system fundamentally operates as follows: an encoder is placed before the input during recording, and a decoder is positioned after the output during playback. This configuration is the same as Dolby NR.
There are two types of dbx systems: the professional dbx I and the consumer dbx II. However, since their basic operating principles are the same, they will be explained together.

During encoding, all levels are compressed at a logarithmic ratio of 2:1. Levels below 0 dB are boosted, while levels above 0 dB are reduced, and this processed signal is recorded onto tape. During decoding, the reverse process is applied, expanding the signal to restore it to its original state.
The concept can be illustrated as follows: if the dynamic range of the tape is 50 dB, in theory, dbx can double it to 100 dB. Levels above 0 dB are compressed to half before being recorded onto the tape. For example, even if an input of +20 dB is recorded, it is effectively compressed to around +10 dB, preventing distortion. In the diagram, the distortion threshold of the tape is set at +15 dB for illustration purposes. In practice, the actual distortion threshold depends greatly on the tape's performance, but this was the general expectation at the time.

When it comes to reducing hiss noise, Dolby B offers a reduction of around 10 dB, which is noticeable but moderate. In contrast, dbx can achieve a reduction of over 30 dB, resulting in what feels like complete silence. For instance, if the tape's hiss noise is at -50 dB, decoding can lower it to -100 dB, which is below the floor noise of the equipment itself.
Moreover, dbx is less sensitive to calibration and level adjustment compared to Dolby systems, making it significantly easier to handle. This simplicity is another major advantage of dbx NR.

In the diagram, the point where there is no volume difference between Input, Tape, and Output—0 dB—serves as an important reference level.
For SATIN's settings, in the case of dbx I, the reference 0 dB corresponds to setting the VU meter to -12 dB.

In the case of dbx II, the reference 0 dB corresponds to setting the VU meter to -16 dB.
These results are based on personal experimentation, so they might not be entirely accurate, but it is important to note that this 0 dB reference is different from the 0 dB in a DAW. Slight variations can also occur depending on tape speed and other settings, so it’s essential to have a thorough understanding when making adjustments.
This is particularly important when using SATIN for tasks such as digitally restoring old tapes encoded with dbx I. In such cases, careful configuration is crucial.

dbx noise reduction (NR) is achieved through the use of an RMS detector and a VCA (voltage-controlled amplifier). In the 1970s, the VCA was a groundbreaking system capable of automatically adjusting gain based on control voltage. David Blackmer, the founder of dbx, is known as the inventor of the logarithmic gain control VCA. While VCAs are widely recognized for their role in compressors, they are also integral to NR systems.

Below is a comparison of hiss noise in a silent state processed through dbx I. It clearly demonstrates significant noise reduction across the entire frequency range. In the high-frequency range, noise is reduced by approximately 40 dB.

When a high-level sine wave is input, as shown below, the hiss noise level also significantly returns. This phenomenon, known as "breathing noise," occurs to some extent in all NR systems and is unavoidable. Each time a sound is played, the hiss noise is lifted along with it.
In music with high sound pressure, this is not particularly noticeable, but it becomes apparent with delicate sounds such as piano or acoustic instruments. The noise accompanying the onset of sound from silence can be distracting. Due to its strong noise reduction effect, dbx is more prone to this side effect, often being considered less natural compared to Dolby. This was especially noticeable with consumer cassette tapes, where less-than-ideal conditions made the issue more pronounced.

Differences Between dbx I and dbx II

As mentioned earlier, the operating principles of dbx I and dbx II are the same. However, their requirements for decks and tapes differ significantly, leading to their division into professional (dbx I) and consumer (dbx II) applications.

uhx Type I(dbx I 1971)

The professional dbx I was introduced in 1971, the same year dbx was founded. While Dolby A had been released a few years earlier, both systems began their industry adoption in the 1970s, marking the emergence of two major players in professional noise reduction technology.
dbx I was designed for high-performance open-reel tape systems and was capable of reducing hiss noise to an extreme degree. However, its stringent hardware requirements made it unsuitable for consumer products. It demanded an extremely flat frequency response across 20 Hz–20 kHz and a signal-to-noise ratio (S/N) of at least 60 dB. Additionally, it required a tape speed of 15 ips or higher.

Below is a demonstration of dbx I processing a challenging noise scenario for NR systems. The settings are modeled after an open-reel setup, but the hiss noise has been exaggerated for clarity. The tape speed is set at 15 ips.
The first segment is without NR, while the second segment uses dbx I.
You’ll notice that the hiss noise becomes nearly inaudible with dbx I, but the unnaturalness of breathing noise may be apparent. Additionally, the sharp attack of sounds tends to change. In particular, dbx I struggles to keep up with strong attacks that emerge suddenly from silence, leading to noticeable delays in its response.

uhx Type II(dbx II 1981)

The consumer-oriented dbx II was introduced in 1981. Unlike dbx I, dbx II was tuned for cassette tapes, which typically had higher hiss noise, slower tape speeds, and less favorable frequency characteristics. Its controlled frequency range was limited to 30 Hz–10 kHz, minimizing its impact on sensitive sounds. However, applying dbx II to high-spec open-reel systems could risk audio degradation.

When dbx II entered the market, Dolby B was already well-established in the consumer noise reduction space, making it difficult for dbx to gain traction. However, dbx II found success in amateur music production, particularly in multitrack recorders (MTRs) designed for home use.
These MTRs sacrificed compatibility with standard cassette decks in favor of professional-grade features like double-speed tape operation and 4-track simultaneous recording. Playback on conventional decks was not a consideration. With frequent use of ping-pong recording techniques, noise reduction provided by dbx was essential for maintaining sound quality.

Using the same scenario as the dbx I sample, imagine processing with cassette tape characteristics. The first segment is without NR, while the second uses dbx II.
You’ll notice that hiss noise is reduced, but the quality is lower compared to dbx I. On the other hand, some might find the sound more dynamic and powerful due to the stronger perceived attack.

The photo below shows an actual dbx II chip. Various manufacturers incorporated these chips into their cassette decks to implement dbx noise reduction (NR).

dbx AN6291, CC0 (cited from Wikipedia)

Next time, we will explore tape-based effects such as tape delay and tape flanging.


The “sound & person” column is made possible by your contributions. For more information about submissions, click here.

achapi

楽器メーカーで楽器開発していました。楽器は不思議な道具で、人間が生きていく上で、必要不可欠でもないのに、いつの時代も、たいへんな魅力を放っています。音楽そのものが、実用性という意味では摩訶不思議な立ち位置ですが、その音楽を奏でる楽器も、道具としては一風変わった存在なのです。そんな掴み所のない楽器について、作り手視点で、あれこれ書いていきたいと思います。
blog https://achapi2718.blogspot.com/
HP https://achapi.cloudfree.jp

u-he / Satin tape machine emulator plug-in

u-he

Satin tape machine emulator plug-in

¥18,700(incl. tax)

Plug-in, tape machine emulator

ブログ有り

お取寄せ

Qty
 
 
 

Categories

Translated articles

Calendar

2025/2

  • S
  • M
  • T
  • W
  • T
  • F
  • S
  • 1
  • 2
  • 3
  • 4
  • 5
  • 6
  • 7
  • 8
  • 9
  • 10
  • 11
  • 12
  • 13
  • 14
  • 15
  • 16
  • 17
  • 18
  • 19
  • 20
  • 21
  • 22
  • 23
  • 24
  • 25
  • 26
  • 27
  • 28

Search by Brand

Brand List
FACEBOOK LINE YouTube X Instagram TikTok