[Paul Frindle]

Originally Posted by ben_allison

Just a point I need to clarify: I totally get inter-sample peaks. What I wanted to know is if they only occur during the D/A process.

No they can occur anywhere the sample stream gets reconstructed into a notional signal. This can happen in filters, some dynamics processors and in EQ's where they are oversampled internally - and such things. The excess signal can theoretically rise to +6dBFS, I have seen real signals rise to +5dBFS, but most errors max out at around +3dBFS

Suppose I have a track with material that has adjacent sample points at 0dbfs, and would (for the sake of argument) create an inter-sample peak of +2. But, this track is going into a mix buss whose fader is down -2.

Problem solved?

Yes it's solved for any gear down line from the gain reduction point (provided that the gain is never raised again) - although I would leave an extra dB or so for security :-)

Or further, what if I have an EQ (pre-fader) across the buss? Assume I haven't trimmed the input, so it's seeing the two 0dbfs samples.

Is it even conceivable that this EQ could clip at +2 since the EQ, being ITB, is only working within the context of a sample rate?

That will depend on the kind of EQ, it's internal processes and what platform it's running on. The EQ may well 'see' the overloads internally, whether it clips or not will depend on the kind of internal headroom it has and whether it is running fixed or floating point. TDM processors (and some other exterrnal processing boxes and cards) are fixed point so they 'may' overload if there is no built in headroom. Host and RTAS processes are normally more tolerant of this and are unlikely to clip because the headroom is provided by the floating value representation.

Are inter-sample peaks even "visible" to most ITB processes since ITB, nothing is technically "inter-sample"?

Yes they are visible where any signal reconstruction is going on. For instance I have made the example of something like a LP high cut filter on an EQ where peaks larger than 3dB above the input level may occur at the output - even though you are 'removing' stuff and not adding anything anywhere and the gain is flat.

Are inter-sample peaks really only important at the mastering stage, when preparing audio to be converted by a playback system?

They are important to an extent everywhere, but the mastering stages are often when they are provoked. This can be bad as it can crack up the consumer's DACs in way you won't hear in the studio. Even simple compression that brings otherwise quieter things up in level (like high hats and percussion - even a vocal voiced quietly) can be major causes of inter sample peaks because they figure more prominently than in the original captured sounds.

The problem of inter sample peaks only occurs because your DAW meters are showing only sample values. Since this a pulse code modulation data stream, these sample values give rise to signal only when reconstructed and decoded. Therefore your meters are wrong and can read less than the signal they will represent after being decoded. There is nothing complex or magic about this at all :-)