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MiniDSP DDRC-88D

gabo4au

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I have a studio monitor setup that is configured like this.

RME UFX II AES output --> MiniDSP DDRC-88D (AES) --> Okto DAC8 Pro (Pure AES Mode) --> Power Amps --> Speakers

The RME is set to 44.1K. It appears that the DDRC-88D is resampling the signal and outputting at 48Khz. Is there any way to change that behavior?

As far as I can tell, the MiniDSP just determines it's sampling rate automatically by looking at it's input, which is from the RME and is 44.1K. I can't find any setting in the miniDSP for it's output rate. Here's what the manual says about the output rate.

"If there is a signal on input channels 1 and 2, all output channels have asynchronous sample rate conversion applied to match that sample rate. Otherwise, all output channels operate at 48 kHz."


The Okto DAC8 also seems to auto set it's rate based on the input stream, the only mention I can find in the manual is that it's free of resampling. So based on that, it should also be set to 44.1k.

However, the main display on the DAC8 shows the sampling rate to be at 48K. Here's a picture of the front panel of the DAC8 showing the 48Khz on the display.

DAC8-Front.JPG



Even though everything seems to be working correctly. I get sound and it all seems to operate as designed. However, I'm wondering if something is resampling the signal, which is not desirable. The only device in the signal chain that has a manual setting is the RME UFX II, which is definitely set to 44.1k.

There seem to be 3 choices of what's going on here.

1. The miniDSP is resampling the signal and changing it to 48K. Based on what I see, this seems to be the case. Even though it should recognize the signal from the RME, which is on channels 1/2 and set everything to 44.1. If that's the case, how can I prevent that?

2. The DAC8 is resampling the signal and changing it to 48K, I don't think that's the case but it could be.

3. The DAC8 has a bug and is just showing 48K on the front panel when it's actually 44.1k. I doubt this is the case, but it's just the only other option.

Any suggestions as to how to make these boxes play nicely would be greatly appreciated. I wish these devices had settings for these things, I find that most "auto set" things don't always work as advertised. Everything sounds really good in this chain, so it's not the end of the world, but I suspect there are some slight improvements to be had if we could remove any resampling that's going on.
 

mdsimon2

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The behavior you describe is a bit odd.

The DDRC-88D will always internally resample to 48 kHz (as described clearly in the manual), there is no way to defeat this. However, it should also convert that internal rate to your channel 1-2 input sample rate (44.1 kHz in your case) on the output which it does not appear to be doing.

The DAC8 has no ASRC and therefore cannot be doing any resampling.

I agree it could be a bug in the Okto but I think it is more likely that the DDRC-88D is not converting the output to 44.1 kHz or for some reason the RME is not outputting 44.1 kHz. I would first try to route the RME directly to the Okto and see if it shows 44.1 kHz, if it does you know it is not a bug in the Okto and you know the RME is actually outputting 44.1 kHz. Assuming everything behaves as expected with the test I would contact miniDSP support to see why the DDRC-88D is not converting to 44.1 kHz. I would say not to worry about it but I would personally want to know what is going on as the behavior is not as expected.

Michael
 
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gabo4au

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The behavior you describe is a bit odd.

The DDRC-88D will always internally resample to 48 kHz (as described clearly in the manual), there is no way to defeat this.

AH, I just found that in the manual. Given this info, it's probably best to just leave it as is, since converting it back to 44.1 after it's been internally converted to 48K would introduce more errors.


However, it should also convert that internal rate to your channel 1-2 input sample rate (44.1 kHz in your case) on the output which it does not appear to be doing.

The DAC8 has no ASRC and therefore cannot be doing any resampling.

I agree it could be a bug in the Okto but I think it is more likely that the DDRC-88D is not converting the output to 44.1 kHz or for some reason the RME is not outputting 44.1 kHz. I would first try to route the RME directly to the Okto and see if it shows 44.1 kHz, if it does you know it is not a bug in the Okto and you know the RME is actually outputting 44.1 kHz. Assuming everything behaves as expected with the test I would contact miniDSP support to see why the DDRC-88D is not converting to 44.1 kHz. I would say not to worry about it but I would personally want to know what is going on as the behavior is not as expected.

Michael

Tried connecting the RME directly to the DAC8 (good suggestion!) and indeed it does show 44.1. So as suspected, it's the DDRC-88D that's not converting it back to 44.1k. The RME is truly a professional product and all the recordings, many tracks/instruments/plugins, all are at 44.1k, so I knew it wasn't outputting anything at 48K.

I don't think I'll contact miniDSP even though it's odd. Since it's being converted to 48K internally, just as well to leave it there until the DAC8 converts it to analog for the amps.

Obviously I would prefer it not being converted at all, but it all sounds great, so I'll take the advantages of DIRAC/Xovers/PEQ over the few problems of the conversion.
 

mdsimon2

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Sounds like a good plan. I agree that I would want it to output 48 kHz to avoid another sample rate conversion. I wonder if the BM plug-in operates slightly differently and this is why it is outputting 48 kHz.

To be honest the design to match the input sample rate on output makes no sense to me when you have the internal ASRC. What is the point of outputting say 192 kHz when you won’t get anything above 24 kHz due to the internal conversion?

Michael
 
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gabo4au

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Sounds like a good plan. I agree that I would want it to output 48 kHz to avoid another sample rate conversion. I wonder if the BM plug-in operates slightly differently and this is why it is outputting 48 kHz.

To be honest the design to match the input sample rate on output makes no sense to me when you have the internal ASRC. What is the point of outputting say 192 kHz when you won’t get anything above 24 kHz due to the internal conversion?

Michael

Very true. I went with the DDRC-88D and a better DAC to get the highest quality possible. Which at this point, I think I have, but this is a limitation of the DDRC-88D that I was not originally aware of.

The UFX can easily record projects up to 192K so if we ever converted to anything above 48K the 88D would be a limiting factor. Fortunately it's unlikely that I would convert the studio to anything above 48K. Rates higher than 48K have a big challenge in handling the project file sizes and very little in way of audible improvements (my opinion!). In today's world, what's the point of recording at 192K when everyone is going to convert your songs to mp3 to play on their iphone :)
 
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