If you want to light a fire in any forum or on social media then start a discussion about audio summing, clocking, or convertors. People have very strong views about these often misunderstood audio technologies. However, what do you think? Take our poll and let us know you opinion.

What Is Audio Summing?

Audio summing is simply combining two or more audio signals together. Since the invention of digital audio workstations (DAWs) there has been a debate between summing inside the box or externally using a mixer. Some suggest that the summing used in DAWs is inferior. For this reason an entire school of thought has been developed around an analogue summing workflow. Products have been created to support the position that analogue summing is superior to the process that takes places inside a modern DAW.

In this short video, sound engineer Ryan West (Eminem, Jay Z, Willie Nelson) tells his story of how he switched from in-the-box mixing to using analog summing. He now uses the Dangerous Music 2-BUS+ and his mixes got "better, bigger, badder, and more exciting."

Some time ago we ran a blind listening test using various methods, here they are with the results:

• The Audio Summing Debate - Can You Tell The Difference? First Test - Neve 8816 16 Channels

• The Audio Summing Debate - Can You Tell The Difference? Second Test - Audient ASP8024 Console Stereo Mix

• The Audio Summing Debate - Can You Tell The Difference? Third Test - Neve 8816 With Width

• The Audio Summing Debate - Can You Tell The Difference? Fourth Test Audient ASP8024 Console

• The Audio Summing Debate - Can You Tell The Difference? Fifth Test Audient ASP8024 Console With Tone Shaping

• The Audio Summing Debate - Can You Tell The Difference? The Results

Do you think analogue summing makes a difference, take our poll now.

What Is Audio Clocking?

Clocking is another subject that has some mystery surrounding it. Who better to explain this than Hugh Robjohns from Sound On Sound. This extract of the larger article Does Your Studio Need A Digital Master Clock? has been used with permission.

Why do we need clocks? The simple answer is that to digitise a continuous analogue audio signal, it must be sampled at precise and regularly repeating intervals. The clock provides that timing information and allows the waveform to be reconstructed as an analogue signal correctly when required (assuming the sample rate is more than twice the highest frequency component of the audio signal being sampled). At its simplest, then, the clock identifies when each sample should be recorded or replayed — and we call that a 'word clock' — but in practice, it often also provides other useful information, such as identifying each encoded audio channel in multi-channel systems. 

If the clock timing varies, the audio samples will potentially be captured (recorded) or reconstructed (replayed), or both, at the wrong time. This, in turn, will result in distortion, so clock timing accuracy is critical in maintaining audio quality.

The diagram on the opposite page Short‑term timing variations between one clock period and the next can result in a distorted waveform.shows how short‑term timing variations between one clock period and the next can result in a distorted waveform. If the timing variations are random, the result is effectively added noise, whereas if the variations are periodic, additional atonal (intermodulation) artifacts can be added to the signal. These timing variations are referred to as 'jitter', whereas a long‑term timing variation of the overall clock rate is called 'drift'. 

There are other kinds of clock too, the most important one being the 'bit clock'. This is used in serial data interfaces like AES3, S/PDIF and ADAT, where there is basically only one 'conduit' over which to pass the audio data: each data bit belonging to a single audio sample is passed one after the other, followed by the bits for the next audio sample, and so on. As binary data, each bit can be either a zero or a one, and it is quite possible for several consecutive bits to have the same binary value. The danger is that the receiving device could lose track of when each data bit stops and the next begins, potentially resulting in corrupted data values being received. To avoid this, a 'bit clock' is transmitted with the audio data to ensure that the receiver remains in sync with the transmitter and recovers each data bit correctly. 

When digital audio data is passed from one device to another, clock jitter and drift are unimportant, provided they aren't excessive, as neither device is interested in the timing of the samples — it has no inherent meaning. All that matters is that the value of each data bit can be recovered accurately, which is relatively easy because each data bit is transmitted for a finite period before the next data bit is sent. So as long as the bit-clock points to somewhere within each static period before the data changes, the data value will be retrieved correctly. Whether that happens in real time or faster (or slower) is of no real consequence to the precision of the data transfer. 

However, clock timing is absolutely critical whenever data is being converted between the analogue and digital domains, so the clocking of A‑D and D‑A converters is of fundamental importance to the quality of the audio. As the diagram illustrates, jitter at either of these ends of the audio chain can cause real problems.

Thanks to Ian at Sound On Sound for giving us permission to use this extract.

When multiple devices are used, such as in a post house or large studio, then a master clock may well be an essential investment, but in a studio with one audio device is it still useful?

Do you think external clocking makes a difference, take our poll now.