Quote from: opsopcopolis on September 30, 2018, 08:06:01 PM
The point that everybody is trying to make is that the above bolded statement isn't how it works. If you set gain correctly, using an HPF is unnecessary and you can pull down the unwanted low frequencies after the fact. This will have the exact same effect as using the low cut on the recording device. The reason the shows you mention sounded like shit is probably because they sounded like shit in the room. If the low cut has a positive effect on the recording, you can have a more accurate positive effect using EQ in post processing. Always.
For example: I taped the Sword about 6 months ago. CA11 omnis > ugly battery box > Sony M10. The low freq content in the room was staggering. I could have put on the HPF on the M10, but then I would just lose that content. Instead, I elected to just pull down the overall input gain on the recorder, allowing me to safely record the show without clipping and give me the option of removing as much of the sub content as I wanted in post. If the show was going to distort at the mics, it would distort at the mics whether I use the HPF or not.
QuoteIf the low cut is something that's built into the mics then that's a different story.
^
Not always, but most of the time.
A HPF will not eliminate all low frequency content, instead it attenuates low frequency content in a linear and predictable way. The important attributes of the filter are it's slope, which is constant across frequency (often -6dB, -12dB, or -18db per octave), and the -3dB point which defines the frequency below which the filtering takes effect. As long as those two specifications are known one can compensate for the filtering afterwards, restoring low frequency content which has been attenuated but is still there at reduced level.. within the dynamic range and the noise-floor limits of of the recording in that low frequency region. In that way a HPF is similar to the low frequency roll off of a directional microphone used outside the proximity-effect region, and how that can be compensated for.. within similar limits.
This might seem counterintuitive, partly because discussion of high-pass filtering on either the microphone or recorder tends to resolve toward three points of view here at TS- use of no filtering or EQ whatsoever; use of a built-in HPF when recording; or application of EQ afterward. What I describe above - use of HPF
along with the subsequent use of EQ to
undo the effect of the HPF afterwards - doesn't fit directly into one of the 3 camps.
Why would anyone want to do such a thing?
A good reason to engage a HPF filter is to enable sufficient mid and high frequency signal level to the recording medium. This is (was) more important to do this when recording to analog tape which has far less dynamic range than digital recording, as well as a less-linear response across other frequencies as the tape becomes oversaturated prior to clipping. If the recording medium could capture the full range of all frequencies at any level, we would not need recording gain controls nor high-pass filters to make recordings which aimed to accurately reflect the frequency balance and and loudness of the live event.* This may bring to mind similar discussions about recording level and recording 16 or 24 bits. As it is, digital recording currently allows us to get away with not needing to engage a high pass filters most of the time in order to get good usable full-spectrum signal recorded, yet we still for the most part tweak the recording gain depending on what we are recording.
^I look forward to the day I don't need to adjust input gain at all with regard to the content I'm recording, needing only to select a microphone and recorder combination that are capable of handling full range of whatever I choose to record, and initially set the input sensitivity of the recorder to that of the microphone. We're close to that already. Some "on-talent" wireless transmitters incorporate proprietary automatic gain-ranging strategies which extend the dynamic range of the system without user intervention. The "dual record" feature on a number of recorders tapers are using which makes a backup safety recording at a lower level is similar, although most will not automatically stitch the two recordings together afterwards to form one with a greater range than either alone. And, mostly out of necessity, many stealth tapers learn initially what gain setting works for the types of music they record and the venues they typically record in, then leave the input-level controls untouched until eventually switching gear, then find a new good middle-way setting. The dynamic range of the microphone>recorder combination just needs to be sufficiently large enough to accommodate the signal level variation between the limits of noise-floor at the bottom of the dynamic range and clipping at the top of the range.
A combination of pre-filtering + post-compensation filtering to help fit the signal to the recording/reproduction medium is much more common than many realize. All tape recordings and playback works this way! All vinyl playback works this way!
As tapers we are not usually carefully constructing our own pre/post emphasis filters that compensate for each other. But we might use a HPF in combination with post EQ to manipulate the attenuated low frequency region- perhaps restoring some of what was attenuated while cutting other parts of it more. Essentially reshaping the low frequency response to the shape we want. This is not relying on the HPF itself to be the correct final filter shape on its own, but using it as one stage of filtering and working with that.
*Most of the time we don't actually want to reproduce direct the frequency balance and full dynamic range of the event, even when people think that's what they want. What we actually want is something that sounds good through the systems we are using for reproduction. We want a credible illusion rather than a true recreation.