Sonnox Fraunhofer Pro‑Codec

Sonnox's clever plug‑in allows you to hear exactly what different MP3 and AAC encoder settings do to your precious mixes — in a true blind test, if you like!

The Fraunhofer Pro‑Codec plug‑in's main real‑time comparison mode.

With every passing year, it seems that, despite the earnest hand‑wringing of audiophiles the world over, more and more of the music that consumers hear has been mangled to some degree by data‑compression algorithms. As such, more conscientious mixing and mastering engineers have got into the habit of rendering and auditioning their work in a variety of data‑compressed formats, to alert themselves to the strengths and weaknesses of different compression algorithms — either so that they can reduce encoding side‑effects with pre‑emptive processing, or so that they can select and configure the most suitable encoding.

Pragmatic though this approach may be, it does suffer from the fact that data‑compression algorithms tend to be offline processes. In other words, you have to render your mix/master, then render a data‑compressed version, and then import both files back into your studio DAW system for comparison. Fortunately, though, respected plug‑in developers Sonnox have now teamed up with Fraunhofer IIS, the original inventors of MP3, to develop the first real‑time data‑compression plug‑in, Fraunhofer Pro‑Codec, thereby providing a means of streamlining this tediously iterative quality‑control exercise.

Real‑time Audio Data Compression

The software is available for both Windows XP/7 and Mac OS 10.5 or above, and comes in AU, RTAS and VST formats. Authorisation is via an iLok dongle and you can choose mono, stereo or 5.1 surround modes. Three tabs along the top of the window switch between its three operating modes: online (real‑time) encoding, offline encoding, and offline decoding. To start with, let me focus on the first of these, since it accounts for the lion's share of the feature set. The basic concept is that you insert up to five different data‑compression codecs into the Codec List slots, and then use the little speaker‑icon Monitor buttons to listen to the effect of each on the audio that is passing through the plug‑in. Alternatively, you can hit the Master In button to compare the currently selected codec with the unprocessed input signal, or listen to the difference between the input and encoded signals (in other words, the audio that the data compression is chucking out) by clicking on the Diff button.

A Lissajous display and dual vectorscopes provide detailed visual feedback about the impact of processing artifacts in the stereo field.Although part of what audio data‑compression schemes do is completely lossless (in other words, removing data redundancy on a purely mathematical level), this typically only cuts file sizes roughly in half. To carve anything else away, you need to start reducing the resolution of the audio information, which inevitably adds noise and/or distortion to the signal. The purpose of psychoacoustic encoding is to funnel these potentially undesirable artifacts into areas of the frequency spectrum where the human hearing system is least likely to perceive them, and it's because this bit of smoke and mirrors is so effective that typical MP3 files can be 10-12 times smaller than their uncompressed PCM source files. However, the more you try to squish the data, the more the processing artifacts, as showcased in the Difference signal, start to impinge unmusically on the listening experience. The aim of this plug‑in is to help you decide which codec produces the most acceptable trade‑off between audio enjoyment and file size.

While final quality judgements should clearly be made by ear, Fraunhofer Pro‑Codec does, nonetheless, provide a great deal of supplementary visual information to support the auditioning process. Central to this is the multi‑function display area that dominates the centre of the GUI. By default, this shows a zoomable, real‑time FFT frequency analysis (the yellow line) of either a single selected input channel or the mono sum of all of them. The red shaded region beneath the yellow line represents the spectral content of the Difference signal, while a set of green lines above it indicates the Noise to Mask Ratio (NMR), a theoretical measurement of how effectively any data-compression nasties are being concealed or 'masked' by the spectral energy of the music itself. The higher up the display the NMR line reaches in any given spectral band, the more likely it is that the listener will detect processing artifacts in that frequency region. Although Sonnox admit that a given individual's subjective impression of artifact levels inevitably won't correlate exactly to the calculated NMR readings, the dancing green line is still useful for focusing your attention towards the most likely spectral 'danger areas', as far as encoding quality is concerned.

When you're working with a stereo input, the Display Type button accesses no fewer than three circular meters. The left‑hand one is a Lissajous display with pink and yellow traces, allowing comparison of the input and output stereo envelopes respectively. The central meter is a faster‑acting stereo vectorscope, which shows the input signal in green against the Difference in red, while the right‑hand meter magnifies the Difference signal to enable closer inspection of the stereo characteristics of any encoding artifacts.

Further information about the encoded files can be gleaned from the three little tabbed pages to the right‑hand side of the Codec List. The first of these (Trim) reveals, for each codec in the list, what is likely to happen to the audio peak level when the encoded file is decoded for playback purposes. It's not uncommon for the peak level of data‑compressed decoded files to increase because of the way each codec's internal filtering routines affect the audio waveform, especially if you're working with mixes that have been heavily loudness‑enhanced at the mastering stage. Therefore this facility can help you reduce the risk of down‑the‑line clipping in the end user's playback device, by alerting you to the predicted degree of overshoot and by providing you with compensatory pre‑encoder gain control. The second tab (Comp) is simple enough, indicating the approximate data‑compression ratio per codec, while the third tab (AB or ABX) provides some nifty tools for ratifying your listening preferences in concrete terms (see 'Blind Testing' box for details).

Recording & Offline Processing

If you fancy blind‑testing your preferences while auditioning different codecs, try the simple AB facility (left) or, if you're really hardcore, the statistically measured ABX testing function (right).

When using the real‑time mode, you can record encoded audio from any or all of the entries in the Codec List, using the five Arm switches in conjunction with the master Record button. If your DAW is already playing back, the Record button engages recording immediately, but if not, the plug‑in obligingly waits until you start playback, to avoid any leading 'dead air' on the output files. Generating encoded files off‑line is also a piece of cake: select the plug‑in's Offline Encode tab and then drag the source file from your computer's OS onto the plug‑in window. You can then arm any of the Codec List entries, as before, and click the Encode button to zap all the files in one go. The Offline Decode tab works similarly, accepting any of the supported encoded formats and translating them into WAV or AIFF files at 16‑ or 24‑bit resolution.

However you decide to create encoded files, the plug‑in can be programmed to add up to six different suffixes to the filenames so that you know which version has been encoded in which manner — a very thoughtful inclusion. That said, there is currently only limited support for adding ID3 metadata to MP3 files, and no option at all for adding AAC metadata.

In Use

Once I'd spent 10 minutes reading up on what the various controls and displays do, Fraunhofer Pro‑Codec was pretty straightforward to use. Everything seemed to work as it should, and the switching was smooth and glitch‑free. The plug‑in's CPU munch varied a great deal depending on the number and type of codecs I inserted, and although normal processor drain measured around the five percent mark, at one point a single plug‑in instance was taking up more than 20 percent of my quad‑core's muscle while I was comparing the different variable bit‑rate options of MP3 in surround. So if your computer still has a floppy drive, you can probably forget about using this software.

The ability to solo and compare the side‑effects of different encoding routines is quite simply a revelation, especially given the additional analysis and metering facilities the plug‑in provides, and it's also interesting to discover some of the processing artifacts that can creep in if the lossless algorithms are fed with unsuitable material. Being able to statistically test subjective impressions about the codecs also provides an excellent perspective — and good ear‑training, too!

Here you can see Fraunhofer Pro‑Codec's offline encoding in action, converting a single, uncompressed source file into five different data‑compressed formats.Despite an overwhelmingly positive experience with the plug‑in, I did experience a few twinges of concern. The first was that because the plug‑in relies so heavily on Fraunhofer's know‑how, there are quite a lot of popular alternative compression codecs not available for comparison — Windows Media, MP2, Ogg Vorbis and FLAC, to name a few. Furthermore, even if you own an offline codec for any of these formats, there's no way to plumb the encoded audio render into Fraunhofer Pro‑Codec's neat and effective ABX test system, which is a disappointment.

I was also peeved that there was no way to record the uncompressed input signal alongside the compressed formats. Most DAW systems will let you bounce the output of your master output channel alongside, but that does seem a little inelegant. You could also argue that including a lossless algorithm in the Codec List could achieve something tantamount to this, but that feels pretty kludgy too. Finally, I was surprised to find that the off‑line encode and decode facilities would only process one source file at a time, rather than allowing batch‑processing of a queue of several. Dragging and dropping a few albums' worth of files one by one is far from exhilarating!

Squeeze Me!

But I don't want to end this review on a sour note, because none of these niggles stops Fraunhofer Pro‑Codec from being an excellent product concept at heart, and one aimed squarely at a wide‑open market niche. Mixing and mastering engineers alike stand to learn a great deal from what this plug‑in reveals, as well as saving a chunk of time into the bargain. While it's not exactly cheap, it does something so useful and unique that Sonnox would probably have had to charge the same again to dissuade me from casting my own plastic vote.