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In foobar2000, before any active DSPs are applied, the decode postprocessors are applied; this can't be turned off unless the component offers that option somewhere in foobar's Preferences.

Deemphasis components come in both flavors (DSPs or postprocessors) so you can control at what stage they are applied.

If I undestand correctly...

	Playback chain:
        file -> decoder -> postprocessor components -> DSPs (if activated in preferences) -> OS/soundcard

	ReplayGain scan chain:
	file -> decoder -> postprocessor components -> ReplayGain scanner

	Conversion chain:
	file -> decoder -> postprocessor components (if enabled in converter) -> DSPs (if activated in converter) -> encoder -> output file.
	Then, output file -> tag copy (if enabled in converter) and ReplayGain scan (if enabled in converter).

Since ReplayGain scanning happens after decode postprocessing, it is probably ideal to not do *playback* deemphasis via a DSP, and to only do it via a postprocessor. For *conversion*, it doesn't matter which you use, because the ReplayGain scanning only happens after the output files are written, i.e. after the postprocessor *and* DSPs have acted on the audio. The converter setup lets you toggle postprocessing (by all components that do it, no way to see which ones they are) and/or activate DSPs; this is separate from the playback DSP setup elsewhere in foobar.

HydrogenAudio user "lvqcl" made foo_dsp_deemph which does deemphasis if it is configured to be an active DSP *and* the file has PRE_EMPHASIS tag value of "1", "on", or "yes". He also made foo_deemph decode postprocessor which does deemphasis upon playback of any file which has the aforementioned PRE_EMPHASIS tag. The current version of each component is 1.1.1 and is available at the first post of the thread at <//hydrogenaud.io/index.php/topic,99394.0.html>.

Meanwhile, HydrogenAudio user "mudlord" made foo_dsp_effect, which originally had a deemphasis postprocessor built-in, but then he moved that functionality out into his own foo_dsp_deemph component which has both a postprocessor and a DSP set in one. The current version of foo_dsp_deemph is 0.2 and used to be available on the foobar2000.org/components page but was removed without explanation. Someone posted a copy at <//hydrogenaud.io/index.php/topic,99394.msg1005123.html#msg1005123>, however. Meanwhile, mudlord's foo_dsp_effect also has an IIR Filter DSP which you can also configure to do CD deemphasis.

Summary:

     component                postprocessor?                   DSP?
===========================  ===========================  =========================
foo_deemph (by lvqcl)        YES (tagged lossless files)        NO
foo_dsp_deemph (by lvqcl)     NO (since v0.20)                 YES (tagged files)
foo_dsp_deemph (by mudlord)  YES (tagged files)                YES (any files)
foo_dsp_effect (by mudlord)   NO                               YES (any files, via IIR Filter)

These are all filters for 32-bit builds of foobar2000, although someone did post a 64-bit build of foo_deemph at <//hydrogenaud.io/index.php/topic,99394.msg1017997.html#msg1017997>.

My choice, for now, is to use mudlord's foo_dsp_deemph for its postprocessing only; it applies to files with the PRE_EMPHASIS tags as described above. I don't use its CD deemphasis DSP. I do have foo_dsp_effect installed, but I am not using its CD deemphasis IIR filter.

Regardless of what you install, you have to be careful to only have one deemphasis filter applied to a given playback or conversion operation. Generally this means you don't set things up such that a DSP's filter is applied when a postprocessor already took care of deemphasis. You also need to be aware that if you have foobar2000 transfer tags after conversion, your new deemphasized files may end up having erroneous PRE_EMPHASIS tags.