miniDSP kits, our answers to your technical questions

[minidsp]

Hi all,

As an effort to keep things organized, let's use this thread for all technical questions you may have about the minidsp kit.

Some other links full of information include: the user manual (although most of us don't read them, they are actually useful ;-)) and FAQ section of our site which will answer most basic questions.

MiniDSP Dev Team

[Iain McNeill]

Hi,
What DSP chip do you use and is there a JTAG connector or other code programming connector? I'm interested in putting my own code on such a board.

Cheers!

[minidsp]

I2S related question by glt from another thread.

Can one bypass the A/D and D/A and only use the digital section? For example, I2S in -> digital crossover -> I2S (high) out and I2S (low) out. What sample rates are supported at the I2S inputs and outputs? For example, can I have 44.1K I2S input and 44.1K I2S output?

read your paper on I2S from your website. It seems I2S is limited to 48KHz and 64 fs. Would it support arbitrary input sample rate and fs with s/w change?

For example one may want to input 44.1KHz, 128fs at the input and 44.1KHz, 256 fs at the output. Most high-end DACs such as Wolfson 8741 requires 256fs with 44.1K material.

Yes, you can indeed bypass the A/D and D/A by feeding I2S signal directly into the board. Making these little kits as versatile and DIY ready was always our intend from day one. See our I2S technical note that you already read as it seems.

I2S is currently limited to 48kHz and 64Fs for a couple of reason:
1) We would need to issue different fw (hence plug-in) to be able to cope with the different sample rate. We do intend to do it, but not right away. Progressive introduction of features to keep a stable firmware is our engineering motto.

2) We also need to modify some on-board components to be able to properly configure the ADC. Easy but may require that either end users do it, or that we ask you to confirm prior to shipping, how you will be using the board. (so not only a software switch as you suggested)

3) Our kit also doesn't have a SRC (Sample Rate Converter )yet! Soon enough, you'll be able to input whatever rate to the board and get it out the way you want.. more to follow in 2 weeks. (gotta leave some surprise somewhere! )

4) Finally, modifying the SCLK (64fs/128fs/256fs) isn't complex so yes, we'll be able to introduce that feature in the plug-in.

Hope this answers your questions

[minidsp]

Originally Posted by Iain McNeill

Hi,
What DSP chip do you use and is there a JTAG connector or other code programming connector? I'm interested in putting my own code on such a board.

Cheers!

Hello Iain,

Great question and glad that you're asking it so early such that we can quickly clarify what this board is and isn't intended for... :-)

miniDSP kit isn't an IDE or eval board from a dsp manufacturer. Why? Because we're not TI/Analog Devices/Xilinx or a multi-national full of tech support able to troubleshoot C code and algorithms. While some of us used to work for such companies, we're just a team of dedicated dudes who love audio, coding and want to provide a finished, working product in the hands of audio DIYers. Support of DSP IDE products takes a lot of time, expertise on hand which equals money. Ever wondered why a Sharc DSP Eval board is costing about 20 times the average BOM? Simple enough, because they account how much time & resources it will take them to support users.. :-)

With miniDSP kits, we aim at building a DIY digital processor community to break the misconceptions about DSP being expensive and complex. Our product is plug&play and no coding knowledge is required. However, this doesn't mean that we only want a simple or fixed structure... Future plug-ins will include advanced features such as having access to all biquads or building your custom filtering with banks of FIR filters (coeff to be entered/calculated by end users). If you have ideas on what you'd like to see, you're always welcome to participate in the community with your ideas.

Hope this clarifies your question. I'm sure that there are plenty of DSP boards out there doing what you would need if you're looking for a DSP eval kit for developing your own C code (drivers/algorithm/UI). Unfortunately, as a community project, that's not what this kit will do for you.

Hope that makes sense (although maybe not along your plans of coding with this board )

[pjanda1]

Wow. I was just about to buy a used Behringer 2024 to use as an EQ for dipole woofers. This might be a better option! The relatively high input impedance is great for us tube guys! A couple of questions:

Is 49Kohm output impedance spec correct? It seems like it would be unable to drive my integrated amps (which have input impedances of 50K), without the addition of a buffer.

With the crossover plugin, it appears you can use both the crossover and EQ functions at the same time, right? Are 12db/octave and 24db/octave the only choices for slopes? Can you apply only one slope per channel? (For example, a 6db/octave low pass at 50hz and a 12db octave at 125hz on the same output).

I'm sure I'll have more as I ponder the unit. Thanks!

Paul
Wild Burro Audio Labs - DIY Full Range Speakers

[minidsp]

Originally Posted by pjanda1

Wow. I was just about to buy a used Behringer 2024 to use as an EQ for dipole woofers. This might be a better option! The relatively high input impedance is great for us tube guys! A couple of questions:

Is 49Kohm output impedance spec correct? It seems like it would be unable to drive my integrated amps (which have input impedances of 50K), without the addition of a buffer.

With the crossover plugin, it appears you can use both the crossover and EQ functions at the same time, right? Are 12db/octave and 24db/octave the only choices for slopes? Can you apply only one slope per channel? (For example, a 6db/octave low pass at 50hz and a 12db octave at 125hz on the same output).

I'm sure I'll have more as I ponder the unit. Thanks!

Paul
Wild Burro Audio Labs - DIY Full Range Speakers

Ooops.. talk about a nice typo on our spec sheet... Real sorry about that and thanks for pointing it out Paul.

Input impedance is actually 6.1k while output is 560Ohms. Apologies for the confusion, accurate datasheet was just updated now on our website. 49K output impedance would indeed be quite limiting...

Yes you can use both EQ and crossover at the same time.
12 and 24dB are currently the only choice, but we're working on the 6dB and 48dB slopes. Just a bit of redesign which takes time. Currently, as we're working on 3 new cards, we're just trying to focus all energy on Hardware. We'll get back to plug-in (fw) very soon and upgrade current plug-in selection for free to all users. (as per our policy).

As for your last question, are you basically asking for 2 low pass cascaded? thanks for clarifying.

Hope this clarifies,

[pjanda1]

Those impedances make considerably more sense! The quick correction makes me think I should get to work on my website . . .

More filter slopes could come in handy, though having EQ makes some fudging possible. I was indeed asking about two low passes (different slopes and different frequencies) cascaded. I suspect that is something most folks won't need, but I figured I'd check. In addition to dipole applications, I suppose cascaded filters might come in handy with some high passes when waveguides are involved. But, that too is a fairly uncommon thing.

Thanks for your quick reply!

Paul
Wild Burro Audio Labs - DIY Full Range Speakers

[transphere]

This blog claims that the board is based on a AD 1701 codec/dsp. Is the board still compatible with AD's Sigma Studio?

I get that you are trying to make an accessible platform using these plugins even a beginner can control. But for the more advanced user being able to go a bit deeper (biquad level preferably) would make the boards more interesting. Since the biquad / parametric eq plugin isn't ready yet, it would be great if the Sigma Studio could be used.

[minidsp]

Originally Posted by transphere

This blog claims that the board is based on a AD 1701 codec/dsp. Is the board still compatible with AD's Sigma Studio?

I get that you are trying to make an accessible platform using these plugins even a beginner can control. But for the more advanced user being able to go a bit deeper (biquad level preferably) would make the boards more interesting. Since the biquad / parametric eq plugin isn't ready yet, it would be great if the Sigma Studio could be used.

That's indeed correct but we're not compatible with AD sigma studio simply because we don't know what their software is doing behind the scene & their software isn't freely available... Programming, reloading parameters at bootup from an eeprom and controlling them from a UI like our kit does requires some FW at the back. Providing the flexibility in customization of the I/O also requires some behind the scene work. The advanced plug-in will come and will give advanced users the flexibility you need. Just bear with us...

[minidsp]

]That really is a big deal - I'd rather avoid unnecessary analogue stages, so I'd like to do all my source selection with digital signals - from my TV, CD player, Squeezebox etc. But I can't guarantee what formats they'll be in - the TV might give 44.1 KHz from broadcast signals, but pass through 48 KHz from the DVD player, the CD player will need 44.1, and the squeezebox will vary song by song depending on the source material.

So, the SRC you're planning will be vital. I have two questions:

1) Will it have a mux so we can feed it multiple sources?
2) How much will it cost? Some existing designs cost as much or more than the miniDSP board itself.

EDIT: Oh, and it'd be nice if we could switch from I2S mode to Analogue In mode in hardware - so, for instance, I could add an FM tuner to source selector.

In answer to your questions:
1) Yes I will have a mux(Hardware controlled) and will have 2 x SPDIF input, 2 x Optical input for the exact same reason as you suggested (multiple sources to receive different sampling rate)
2) As for cost, not finalized yet as we're still waiting to get all costs from our suppliers. I'm hoping to start production in 2 to 3 weeks. It will definitely be cheaper than a miniDSP though.. Like any of the I/O cards intended to stack on the miniDSP (the brain), the idea is that you get a brain, and can "lego" your setup as you wish.
3) Finally, we won't be able to toggle that board via hardware from analog to I2S. Maybe in the future with another board. The Digital I/O will have a jumper/switch where you can select if you want the board to be Master or Slave (depending on how it will fit in your setup)

Hope this makes sense.