Accessories , ex-demo

Dolby 361 Module Trick Vocal Stressor

Dolby 361 Module with Dolby Trick Vocal Stressor mod cards ! Karten (by EMI from XLR to Hirchmann plugs customized)  XLR adaptercables included (IN and OUT)

We have several options Dolby 360, Dolby 360 with Gain Pot, and stereo systems with all cards. Contact us for more than one, or other Dolby Vintage products.

Hardware Setup :

Audio routing

  • DAW (effects send, bus, etc) —> audio interface —> Dolby “line in”
  • Dolby “to rec” output —> audio interface —> DAW channel line in

Send the signal to the Dolby & record the output.

You’ll need to compensate for the audio interface latency


Hardware level calibration

  • send tone to Dolby in Rec mode, NR out
  • set output level for unity gain using multiturn output level pot behind front panel

Hardware setup for Dolby Trick

  • Set NR in and Rec on (white & red buttons pushed in)



If you’re using a standard Cat.22 Dolby A card the output of the 361 will be the encoded signal – ie the original signal plus the processing. This means balancing the effect will take a bit of juggling with levels to get the desired effect


How it works

As you reduce the level going into the Dolby the effect will increase. Dolby A encoding uses a multiband expander so more level = less effect, the inverse of a compressor, and the inverse of the decode process. For the Dolby Trick there is no decode process, just encoding

The NR in / out switch should give an obvious effect if you monitor the return signal. If you hear no effect, reduce the level into the Dolby

This Cat 22 Dolby A card has been modified as a “Dolby Trick” card. In this modified card bands 1 & 2 have been disabled so only bands 3 & 4 – the mid & high frequencies – are processed. Use in encode (record) mode to process audio


The Dolby 360, and the later 361, was ubiquitous throughout the 1970s, 80s and 90s. It was the standard single-channel Dolby mother unit, compatible with the original 1965 Cat 22 Dolby A card and the later Cat 280 Dolby SR cards. Every studio had a couple of 361s but they are now surprisingly rare on the secondhand market

As a double-ended noise reduction system, Dolby A encoded the signal and applied reciprocal decoding on playback. If the tape machine was aligned correctly the system was pretty transparent and gave a significant noise reduction, particularly at higher frequencies

Post-digital, Dolbys are obsolete except for archiving and for doing the Dolby Trick. Dolby A splits the audio spectrum into four bands, applying varying amounts of compression to each. Compression is level-dependent so, as levels rise, compression backs off. At higher frequencies, where tape hiss is more obvious and average signal levels are relatively low, a fair amount of compression could be used, resulting in a dramatic perceived reduction in tape noise & hiss

The Dolby Trick

The Dolby Trick uses the high-frequency compression of Dolby A as an audio effect. By encoding the signal, but not decoding it, it lifts the harmonics & airiness of sounds in an attractive way. It works like a charm on backing vocals but it’s also useful on guitars, drum ambience & etc

Used with standard Cat 22 cards the effect is subtle. We have modified the Cat 22, bypassing processing on the lower two frequency bands, to create a more pronounced effect

The Dolby® A Trick

The Dolby® A Trick was a technique used in the late 60s and early 70s to enhance the top end of recordings, especially vocal tracks, by using the encoding stage of a noise reduction unit.

Noise Reduction or Enhancer?

Introduced in 1966 with the Dolby® A301 first, and then in 1970 with the Dolby® 361 (with the CAT 22 card, in photos), the A-Type noise reduction was quickly misused and modded by engineers to enhance their recordings by using the encoding stage only. The most common mod consists of disabling the two lower bands so that only the high-frequency portion of the signal is compressed, giving even more air to vocals. This technique was labeled with many names like the Vocal Trick, Air Hack, Stretch Mod, Vocal Stressor, and even the “John Lennon mod”.

How does it work?

To limit the amount of noise generated by tape recording, early noise reduction systems used what’s called a multi-band compander (compressor/expander).
The unit dynamically emphasizes the high frequencies during the encoding stage (recording to tape), so that during the decoding stage (playback from tape) the signal is attenuated, along with the typical tape noise. By using the encoding stage only, you can obtain a natural enhancing effect, increasing the top end of any track.

As you can see from the picture above, in the encoding stage, the input signal is split into 4 bands (with the highest bands overlapping), dynamically compressed, and then summed back with the dry signal. The amount of compression on each band is inversely proportional to the volume of the band. Quieter sounds get brighter while louder sounds remain almost unchanged.
This adds brightness and air without generating any new harmonic content or distortion, resulting in a more pleasant and natural enhancer compared to a typical exciter.


The bands are divided as follow:

  • Band 1 has a low pass filter around 80Hz.
  • Band 2 is the results of the input signal minus band 1 and 3, essentially a band pass filter from 80Hz to 3kHz.
  • Band 3 has a high pass filter around 3kHz.
  • Band 4 has a high pass filter around 9kHz.

These bands were chosen by Dolby® for level content and its effectiveness in eliminating tape hiss in the record/playback process. The overlapping high bands (3 and 4) work very well for the enhancing process.