“Ambient Stereo” recordings? Are they good or bad for opera?


Recently we became aware of this process, and wonder what it means for opera. We are hoping it does not signal an era of “Autotune”…

Opening up the comments for this one, what do you think?

What is “Ambient Stereo”?

In the late spring of 2008 we became aware of a new development in audio processing software, which allows a mastering or remastering engineer to excert a considerable degree of control over the ambience in a recording – that is to say, the studio, room or hall echoes and reverberation contained within almost all music recordings. When working with stereo material it gives the mastering engineer precise and fine control over perceived depth and width, for example.

With mono recordings, such as the vast majority to be found at Pristine Classical, it offers something quite new – and sonically very interesting indeed. Now we have the ability to extract from a mono recording that same room ambience and spread it into the stereo field – in a very natural and neutral way. The direct signal (i.e. the original mono sound of the musicians) is preserved and is tonally unchanged. What appears to the listener is a whole new sense of place, and a degree of “air” around the performers which is entirely believeable and consistent with the recording.

(See below for more technical information on the processing used to make Ambient Stereo recordings.)

It’s now a few years on – has anything changed?

More recent recordings from Pristine, from 2012 onwards, have in some instances also benefited from a new reverberation system, called “convolution reverb”. Unlike a conventional digital reverb, here the acoustic properties of some of the world’s finest concert venues – opera houses, symphony halls, chamber music recital rooms, churches and cathedrals – have been mapped in such a way as to allow them to be applied to a recording. The impact on older, “drier” recordings can be truly amazing!

The acoustic mapping places the listener at a specific seat (normally the best in the house) and the recorded performance benefits not only from the reverberant sound of the hall, but also the specific acoustics of the walls, ceilings, chairs, acoustic treatments and so on which give the greatest concert halls their own disctinct and special sound. Thus the sound of an opera house tends to favour voices, with shorter reverb times and an acoustic which helps clarify the singing, whereas a symphony hall helps to round out the sound of a large orchestra in a highly pleasing manner. Meanwhile, the lengthy echoing sound of a large stone church is ideal for organ recitals.

With this new technology, alongside our existing Ambient Stereo treatment, we’ve taken a major step further in bringing older, mono recordings new life.

Isn’t this just the notorious ‘fake stereo’ of the 60’s in another guise?

No. Just about all previous efforts at creating some kind of stereo from a mono recording involved all sorts of potentially destructive sonic manipulation. Comb filters were commonly used, sending instruments flying around the stereo soundfield as they changed notes, and screwing up any mono compatibility. Additional reverberation was added, more often than not sounding less than natural, with the risk of creating the unnatural sound of “a room within a room”.

Our Ambient Stereo recordings avoid all of this. The centre image is exceptionally stable. The signal highly mono-compatible. There is no artificial generation of reverberation, as only that which is contained within the recording is heard – ‘dry’ recordings stay dry; reverberant recordings remain equally so. The processing is based on a US Patent which is at the cutting edge of digital audio processing research, creating in our Ambient Stereo recordings a transparent and open sound which is ideal for both headphone and loudspeaker listening.

What do the professional expert listeners say?

In the days and weeks prior to our decision to offer Ambient Stereo recordings as an alternative to our regular mono remasterings we carried out a lot of listening tests, and offered a number of experts, audiophiles and enthusiasts the opportunity to listen to the effect. Naturally some raised doubts over what they heard, but the majority response was very positive, especially given the notoriety of the so-called “fake stereo” recordings of yesteryear.

One highly respected reviewer from Fanfare magazine, Lynn Bayley, with admittedly only a 5-minute exerpt from a single, unfinished Toscanini recording to go on, was immediately impressed:

I have to admit that I was not at all prepared for what I heard. It seemed to me that by subtle spreading the tone across two channels, you have “filled in” sonic gaps that make the PERFORMANCE – for me – much more valid than any of its monophonic issues. I’ve often complained of what I heard as a static, station-to-station performance of the 9th in this studio recording. That static quality is, to my ears, completely eradicated by your transformation.

Yes, I think you should process the entire symphony this way and issue it [we have!]. And, if you don’t mind my suggesting it, there are four other Toscanini recordings of the same vintage that would greatly benefit from this treatment as well…

Meanwhile Peter Joelson, who writes for a number of music publications on both sides of the Atlantic, was sent both the mono and Ambient Stereo releases of Kathleen Long’s Fauré Piano Pieces release, (PAKM015). After some careful listening, he wrote back:

Listening to these through my main and active system which images tightly showed a subtle difference between the two masterings. The Mono tracks were pleasant to listen to, though switching CD to the Ambient Stereo mastering did add depth to the piano’s sound. The piano itself did not seem to me to be affected at all by the process; the image remained stable and seemingly identical, though it felt more three-dimensional, and there is no more reverberation than in the Mono mastering. The piano did not wander across the soundstage, nor were the frequencies redistributed as in older electronic stereo processing with which this should not be confused. As the term makes clear, it’s the work on the ambient sounds which gives the sound the effect of greater depth.

While the effect is subtle through speakers, I found the difference is more startling when listening through headphones, as would be done with a portable player. Here the ambient processing means the sound is much more comfortable for me to listen to than the straight Mono, and yet again the piano itself seems to me identical in sound.

Were I to do much of my listening by means of a portable player and headphones or earspeakers, I’d certainly be more satisfied by the Ambient Stereo mastering, as listening in this form is simply less tiring.

So how does it actually sound?

Ambient Stereo XRTry Ambient Stereo for yourself (alongside all our different download options): we have a free download of Alban Berg’s String Quartet, Op. 5 here. It’s a ZIP file of the Juilliard Quartet’s early 1950s recording (PACM087) and it includes Ambient Stereo versions in 320kbps MP3, 16-bit FLAC, 24-bit FLAC, and a mono 16-bit FLAC. Listening to them all will give you a perfect introduction not only to Ambient Stereo, but also to our different download formats.

Further technical information

The software used for this Ambient Stereo processing was created by German digital audio signal processing experts Algorithmix®, using a US-patented process developed by renowned mastering engineer Bob Katz, called K-Stereo.

In their own words:

K-Stereo is a patented psychoacoustical process (US Pat.7076071) that extracts the ambience inherent in ordinary recordings, and is capable of spreading that uncorrelated ambience around the soundstage, and enlarging the size of that soundstage, both deeper and wider.

In addition, K-Stereo enhances the depth and imaging of the instruments and vocals without adding any artificial reverberation. It does not have a sound of its own; it just enhances the existing ambience and early reflections. K-Stereo is also capable of making a natural mono to stereo conversion.

K-Stereo … performs natural mono-to-stereo conversion, by bringing out the ambience in the original mono source and spreading it to the sides in a stereophonic fashion, and with an extremely mono-compatible result.

For further details you can visit the K-Stereo homepage at Algorithmix’s website here.

Convolution reverb is handled by Waves IR-1 Parametric Convolution Reverb – more details from the software house can be found here.

Information provided by Pristine Classical

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