Phædrus Audio Listening Room

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Pro-audio products Historic recordingsHi-fi productsVinyl revival


Vocal sessions - PHAB preamps

The following tracks were all recorded with a tube microphone (Rode NTK) and the original, hand-built London Console which was designed to re-create the famous mixers of the 1960's. No compression was employed (beyond carefully "riding the faders"). It was the success of the London Console in producing a unique and "different" sound that Phædrus Audio was formed to make the various parts of the console: mic amps; EQ; vari-mu compressor; and stereo Shuffler available as modules as part of the London Series and now available in the PHAB-S and PHUSION rack-mount products.


    A spoken word example (from Scroggie's wonderful Foundations of Wireless). No processing at all: just a tube mic' and the PHAB / PHAB-S preamp'.

    Here is a example of a vocal recording of a song from the musical Copperfield. Not the well known jazz-standard, this is the character Steerforth's song from the second act of the play.

Pop and rock sessions - PHAB, PHAMULUS and PHÆDRUS EQ

The following tracks were all recorded with the original Perfect Pitch Music London Console and were deliberately recorded with - and in - a 1960's style. All instrument amp's were largely miked and DI was avoided as much as possible, except for the bass.

    Nuova Vita - Guitars all miked (with PHABs); lead compressed with PHAMULUS; bass DI (with PHI/PHUSION). Samples direct to mixer via PHAB preamps at line level. EQ'd with PHILTER/PHUSION.

   Tar Tin - Guitars all miked (with PHABs) and compressed with PHAMULUS; bass DI. Samples direct to mixer via PHAB stages at line level. EQ'd with PHILTER/ PHUSION.

    Báid Fliuch - One guitar (Strat') amp'ed with Electric Road amplifier, miked with PHAB preamps, recorded twice, lead compressed with PHAMULUS. EQ'd with PHILTER/PHUSION EQ.

    Doggone - Attempt at getting a sixties guitar-group sound. Listen to those overdriven Vox amps (captured via PHAB preamp's). EQ'd with PHILTER /PHUSION.

The Other Side of the Sixties

We wanted to have a try at getting some classic "Easy Listening" sounds with the London Console. It also gave us an excuse to come up with an easy-listening album cover too! Here are some of the results from the sessions.

    Catamarano - A theme to accompany the Jet Set. Synths and samples via PHAB preamps. EQ'd with PHILTER / PHUSION.

    Trab im Schwarzwald - Something cheesy. All sampled instruments via PHABs preamps. Bass DI (via PHUSION), compressed with PHAMULUS). Guitars recorded (PHAB preamps). EQ'd with PHILTER /PHUSION.

    Surfing Sundae - Plectrums in overdrive. Electric Road amp'; PHAB preamps; Bass DI (PHUSION). EQ'd with PHILTER/ PHUSION.

SHUpHLER - classical (Shuffling) demos

Some brief musical extracts of the various Shuffling techniques are given below:

The shuffling technique selected when the SHUpHLER is set here is an entirely new technique and is intended to compensate for various shortcomings in crossed-cardioid recordings which are usually accused of lacking "spaciousness". We call it "Phædrus Crossed Fours" or "Rectified Cosine microphone technique" and you can read more here.

    The first part of each musical extract (taken from rehersal tapes, note the false entry!) is the signal direct from the microphones and the reprise is treated with the "crossed four" process.

    Here is another demo of the "Phædrus Crossed Fours" or "Rectified Cosine microphone technique"; this time in a very reverberant acoustic.

I tried it on several recordings made with a Schneider disc (a variation on the Jecklin disc theme) and noticed distinctly more precise imaging focus and a lovely low-end ‘bloom’ and depth, which seemed to make the recording more real and natural somehow. It was broadly beneficial when applied to ORTF (near-spaced cardioids) recordings, too, again improving the focus and depth.
Blumlein δ The greater part of Alan Blumlein's (1933) patent is concerned with a binaural stereophonic microphone arrangement in which two omnidirectional microphones are spaced about 8 inches apart (like the ears). Signals from microphones so arranged tend to produce excellent stereo on headphones, but disappointing results on loudspeakers. Blumlein contrived a theoretically sound and practical system for treating these signals for loudspeaker replay. The Phædrus Audio SHUpHLER has a modern implementation of Blumlein's original "shuffler" when the switch is set in the Blumlein δ position.

    Once again, the first part of the musical extract is the signal direct from near-spaced omni microphones and the reprise is treated with the Blumlein δ process.

Stereo - what can the matter be?
FRANCI - This SHUpHLER incorporates a modern (yet still completely passive) implementation of the Stereosonic Shuffler in which the uneven frequency-response and group-delay problems of the original implementation have been entirely resolved. This is the shuffler known as FRANCINSTIEN. An example of the FRANCINSTIEN Shuffler process is given here.

    The first part of the musical extract is the signal direct from crossed-cardioid microphones and the reprise is treated with the FRANCINSTIEN process.

BoF - The Stereosonic Shuffler actually over-compensated for the theoretical correction required for pure, "pan-poted" stereo, multi-track recordings. This is possibly because the EMI filter was intended only for stereo recordings made with stereo microphone arrays. This is the motivation for another, completely new, Shuffling process called Bride of FRANCINSTIEN (or BoF). All the theory behind this is given here.

    The first part of this musical extract is the signal direct from the mixer and the reprise is treated with the Bride of FRANCINSTIEN shuffler process.

For the very latest in what's possible with stereo shuffling, go to our FRANCINSTIEN WARP demo.


The equalisation available in the PHUSION (or PHILTER) has its own demo page.

Some of the PHUSION equalisation settings (as well as the preamp colouration) are encapsulated in free impulse responses which are made available in the Phædrus Impulse Response Library.

..... it’s hard to beat [The PHUSION EQ] for subtly shaping and polishing a mix, and with switched values allowing easy comparison of different settings I found it a real asset when mastering.

PHUSION preamps demo

The PHUSION is equipped with four microphone preamplifiers for each channel. They are: a classic tube preamp; British germanium transistor preamp, British modified hi-fi transistor preamp; American discrete op-amp preamp. Each has a very different character as demonstrated in this video.

I found selecting different Phusion preamps and juggling the input and output levels allowed a wide range of tonalities, from pretty transparent, to subtle amounts of body and warmth, to really quite crunchy and edgy. This range of different sound characters combined with the easy controllability is what makes the Phusion so special.

PHAMULUS Tests and examples

It's hard to judge a compressor in a mix unlike a preamp, in which case the tone is evident. So here are a few tests of the PHAMULUS compressor. Once again, the original track segment is played first followed by the version treated by the PHAMULUS afterwards (the exception being the technical track, see below).

    Electric guitar test.

    Used across a very simple mix.

   Vocal test.

And here for the techies, here is a series of sine wave tests ramped and burst which demonstrate the level and dynamic performance of the compressor (release set to position 3 which is equivalent to the minimum Altec position). Input is on the left, output on the right. The waveform of the file is instructive (see right).

The Phamulus .... is, in its own right, a very good vari-mu compressor. Apart from a couple of 500-series products that aren’t directly comparable, the Phamulus is, by a long way, the most cost-effective example of that genre that I know; it offers a performance package that is seriously good value for money.

Electronic TubesTM

Here's an audio file to hear the difference between an alternative VF14M replacement (recorded first) and the Phædrus Audio VF14M Electronic TubeTM (recorded second).

A second example which demonstrates the difference between a new VF14M Electronic TubeTM and an old German tube. In this example audio is fed to amplifier via a capsule simulator as explained here. The audio captured with the German tube as the amplifier (played first) has been further amplified in the DAW to bring it closer to the gain of the Phædrus Audio VF14M Electronic TubeTM (which appears second). Low mutual conductance (gm) is a classic fault in an old VF14 tube and this causes the impedance-converter gain to fall far below the Neumann specification for the U47 (U48). Unfortunately, noise performance in a tube is related to the reciprocal of mutual conductance, so low gm means lower-gain and higher-noise.

Historic recordings & archiving

Here we are concerned with the combination of the Phædrus Audio Groove Sleuth Mk. II preamplifier and the needle-drop/archive software Stereo Lab from Pspatial Audio.

A de-clicker for audiophiles

Stereo Lab incorporates an audiophile de-clicker doesn't interpolate or predict the audio. Instead, a robust click-detection algorithm is coupled to an adaptive attenuator which lowers the intensity of clicks rather than attempting to remove them altogether. In this way, audio is never lost or synthesised.

The Stereo Lab detection algorithm is virtually foolproof. It is biased against detection so, in the event of an ambiguous detection it will rather let a click go through than replace good audio.

Historic equalisation (LPs)

This record was made in the 1950s on DECCA's then state-of-the-art recording system known as FFRR for Full Frequency Range Recording but before the switchover to RIAA equalisation.

Early Decca LPs of this period used the Decca 33⅓ recording characteristic (500C-11.5). If RIAA equalisation is used to reproduce these discs, the bass is over-boosted and the treble muted. Pspatial Audio's Stereo Lab has equalisers which are optimised for Decca records.

The examples below are in two parts. The first part is a recording of an all analogue needle-drop recorded via a very high-quality RIAA pre-amplifier. The second section is the same short musical segment recorded with Groove Sleuth preamplifier and processed via Stereo Lab.

In this case, the software was responsible for the DECCA EQ correction and the click removal.

Demo 1 - from the Adagio introduction to movement 1 of Dvorak's Symphony no. 9 in E minor (From the New World)

Things to listen out for:

  • Over boosted bass which exaggerates the recorded rumble on this disc. Compare 0:01 - 0:06 with 2:16 - 2:19.
  • Also over boosted bass and timpani in bars 9 to 14 (1:05 - 1:30, compare with 3:19 - 3:45).
  • Note the woodwinds in bars 6 to 9. There is much better focus to the sound at 2:53 - 3:16 than at 0:39 - 1:00.
  • Note also that details such as the cough during the bar 4 horn call (2:47) and the conductor's cue before the ff in bar 9 (3:18). Both are very hard to hear in the analogue needle-drop.

Demo 2 - from the famous Largo

  • Once again, note the reduced rumble and surface noise in the Groove Sleuth & Stereo Lab version. The tape edit is even audible at the beginning of the track (1:39). It's quite impossible to hear this in the analogue recording.
  • Over boosted bass making the timpani in bar 4 very boomy in the analogue version (0:27).
  • Note the better focus to the cor anglais solo in the Stereo Lab version. This is especially apparent when the clarinet joins in bar 11 (2:52).
  • But perhaps the most striking difference is the massive click during the A major chord in bar 3. This is absolutely atmosphere-shattering in the analogue recording yet almost unnoticeable in the Stereo Lab processed version.
Demo 3 - Noise levels

A demo for the technically minded this.... The track contains a recording of the residual noise of the LP capture system, before the needle is placed on the record and then after. Once again, the first is with a high-quality analogue set-up: the second via the Groove Sleuth, the PHLUX active cartridge and Stereo Lab. The track is boosted in level by 30dB above normal so as to make the differences easier to hear. Note that:

  • With the Groove Sleuth, PHLUX & Stereo Lab, the noise level is very, very low and massively beneath the vinyl record noise-floor.
  • And once the needle has been lowered onto the record, the click-reduction algorithms reduce greatly the background noise off the disc itself.

All of which means, when you process needle-drops with Stereo Lab, you're listening to the music, pure and separated from the noise mechanisms which surround replay from records.

78 RPM records and Graδient noise-reduction

Unquestionably, the most important technical advance in the history of recorded sound was made in 1948 with the introduction of the plastic, long-playing (LP) record by Columbia Records.

Nevertheless, the recorded legacy of eighty years of planet Earth exists on the "78 RPM" records which predated LPs. So we need to take them seriously and see how the information might best be teased from their rough grooves!

Equalisation of pre-LP (or shellac-era) records

There appear to have been a plethora of recording characteristics used during the shellac period (and possibly even more opinions on those characteristics!). In all cases Stereo Lab provides the appropriate equalisation curves.

Crackle remover

Seventy-eight records exhibit pops and clicks of a very short duration and which are present almost all the time. We call them "crackles". The Stereo Lab crackle remover is automatically adaptive and is very effective. Unlike so many other, competitive techniques, the crackle-reduction has no effect on the high-frequencies so that the sound is not "dulled" when it is cleaned-up.


GRAδIENT stands for GRAmophone DIsc Enhanced Noise Treatment and is a unique noise-reduction process for shellac-era needle-drops introduced for the first time in Stereo Lab.

    A final demo is here and brings the various advantages of software processing together. The first half of the file is a recording of Ravel's Introduction and Allegro for Harp* recorded via a hardware preamplifier equipped the appropriate 500N-flat equalisation for a British Columbia release of the period. The second half is the same music recorded as a flat-response needle-drop using Groove Sleuth Mk. II and processed in Stereo Lab using the correct equalisation, crackle removal and GRAδIENT. The differences speak for themselves!

*Columbia DX 1310, DX 1311. with string quartet, flute and clarinet; harp solo by John Cockerill

Hi-fi products


The stereo correction techniques collectively known as FRANCINSTIEN have been continuously developed since the 1990s when the first, passive matrix was produced and sold by Perfect Pitch Music.

The most radical improvement comes with the incorporation of findings derived from a theoretical analysis of a stereophonic sound reproduction system as a sub-optimal wavefront reconstruction system which post-dates the original research which informed the original Stereo Shuffling techniques by thirty years.

The result is the FRANCINSTIEN WARP (for WAvefront Recontruction Processor) ...... What does it sound like?

Here unprocessed and FRANCINSTIEN WARP processed musical examples may be A/B compared. Some browsers may not parse this, so the two audio files are available as separate examples below.

Original audio FRANCINSTIEN WARPed


Or, in a non A/B format: the first recording contains various samples of music, the second, the WARPed examples.

Here, the same examples have been processed by FRANCINSTIEN WARP.

The Vinyl Revival - DisC

In this section we have a demonstration of DisC, Phædrus Audio's displacement sensitive cartridge which does not require RIAA correction and its thereby ideally suited to the highest-quality real-time replay of analogue records.

Here the DisC (and PHATHOM base station) are compared with a respected moving-magnet cartridge in the same price bracket.

    Here's the results from the moving-magnet cartridge coupled with a standard RIAA preamplifier.

    And here's the DisC-PHATHOM combination.

A/B test

This section is βeta. It does not work in all browsers.

Track 1 (DisC): stopped
Track 2 (MM): stopped

Listening to: nothing

Here, the same two files as in the example above are arranged to play simultaneously. A button ("Toggle") enables you to switch between the two recordings; enabling you to A/B compare the MM cartridge with the Phædrus Audio DisC.

Track 1 is the DisC: track 2 the MM.

Read a new article by Richard Brice about the DisC cartridge and how it works.

Original tracks on this website © Perfect Pitch Music 2012 - 2017. All rights reserved


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