Based on manual it is my understanding that it is better to set input to 24 bit if digital source EVER provides 24-bit. Being that my Mac mini music server does sometimes provide 24-bit audio and my PS4 Pro can provide 24-bit DTS bitstream, it seems best to have it set to 24 bit input (to accept 16-24 bit inputs) and upscale everything to 24 bit (when needed) before outputting to 568.2mm set to 24 bit input. Or is this an incorrect understanding of the manual?
If the 518 is set to 24P24, 16-bit (or any) input will not be enhanced to 24-bit, it will just pass straight through, other settings like Gain etc. will still have an effect.
It may be worth setting up separate sources (some call them phantom) for the different files and switch to suit.
Thanks for this insightful information. Just re-read this section of manual and it does indeed seem that I misinterpreted what it was saying. The vast majority of my digital audio collection is 16/44.1 CD rips in FLAC so will leave 518 set on 16P24.
And with using “Gain’ setting instead of “Emphasis” setting? Emphasis seems to be the recommended setting for most media types.
Emphasis will change the frequency response, similar to a RIAA curve on vinyl, dolby NR on cassettes, in effect boosting the number of bits for high frequencies. But it should only be used with DACs that can de-emphasise (preferably in the analogue stage) and I don't think Meridian processors do.
Gain is useful for upping low output signals, optical out on a TV is a normally a good candidate, most are 8dB down.
Both emphasis and gain can cause clipping of the digital signal.
Very insightful too. Will do some research to see if 568.2 de-emphasizes incoming digital audio. If not then I’ll switch to Gain mode. Read on an older thread that +6dB seems to be preferred over +5 or +8dB as, for some reason, +6bB is the most conducive to processing. Will experiment with this today, but being that my source is a computer perhaps no additional Gain is needed?
Also, the last two settings in Config menu aren’t disused in manual: (1) DA Y/N (currently set to Y as presumably DA means “digital audio”?) and (2) DTSXX (currently set to DTSCD).
Info I had in my notes from years ago:
If you have a Meridian 518 Digital Processor, this will de-jitter a DTS signal for optimum sound quality.
However the resolution enhancement features of the 518 are not appropriate as DTS is a compressed digital stream, not standard digital audio. Hence your 518 should be switched to Bypass mode prior to listening to a DTS CD or LaserDisc.
There is an upgrade to the 518 software, Version 1.2, which allows it to detect a DTS stream. In this case, the 518 automatically selects Bypass when DTS is detected.
Version 1.2 adds four DTS modes to the 518 which can be assigned to sources in Config. The modes are:
· DTSMU – 518 mutes on receipt of DTS (used when 518 is a preamp).
· DTSCD – detects DTS with a normal strategy and selects Bypass.
· DTSLD – detects DTS with a rapid strategy and selects Bypass.
· DTSMA – mastering processor mode ignores DTS.
These can be selected according to Type as follows:
· Type 0 – all sources DTSMU
· Type 1 – all sources DTSCD except DVD and LD which are DTSLD
· Type 2 – all sources DTSMA
Thanks heaps for this info. Makes sense as when I select DTS source the display shows “DTS” instead of gain number. Thinking I’ll not run my DTS source through 518 as there doesn’t seem to be any advantage to doing so (eg, will just go directly into 568.2mm via Toslink).
Firmware is version 1.22 but might have a lead on an upgraded ROM chip (presuming it is worth the effort to upgrade to 1.25?
I thought 1.22 was the final version?
You are indeed correct. I had misremembered and thought 1.25 was the latest. Very glad to know that this used unit already has the latest firmware version.
There seems to be mixed opinions about the 518 adding any benefit if placed before 568.2mm processor, which, apparently, applies Shape C noise shaping to all incoming digital sources anyhow (quote from older HH forum thread):
“Here is the answer I received from Ken Forsythe at Meridian in Atlanta:
The 518 has multiple dither/noise shapes as we did not know what DAC it would be in front of. The 568 does employ dither (in the upconversion to 24 bit) and noise shaping (SHAPE C) to maximize it's internal DACs or the DSP speaker's DAC. We have not found any audible advantage of placing a 518 in front of a 568.”
In light of this, perhaps if another noise shaping curve is applied by 518 then this could synergistically interact with the Shape C applied by the 568? Perhaps this is why 568 users tend to report the best sound when setting 518 to Flat because 568 is subsequently applying Shape C and, thus, if some noise shaping other than Flat is used by 518 it simply doesn’t jive?
In addition to the potential noise shaping synergy, it is my understanding that the 518 and 568.2mm employ twin PLL and FIFO de-jittering methods, respectively. If this is indeed the case then perhaps de-jittering digital sources with twin PLL (518) before subsequent FIFO de-jittering (568.2mm) also results in a synergy that yields even less jitter than would be achieved by the 568.2mm alone (i.e., “sounds better”)?
Will continue to experiment with different 518 setting (before 568.2mm) to see if any of them result in audible improvements. Current setup offers relatively easy switching of output from 3 way Toslink switcher between 518 and 568.2mm so will also experiment with listening to: (1) source > 518 > 568.2mm and (2) source > 568.2mm.
Thanks again for the insightful replies, very helpful indeed!
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