KanoMaster22
Posts: 191
Joined: Wed Oct 05, 2016 6:06 pm

Pi Portable Recorder - Project Progress

Wed Jun 27, 2018 10:28 pm

This thread will be updated with progress on my Pi Portable Recorder to record progress.

Parts list:

Audio Injector Ultra 2 (available on Kickstarter)
Pi Zero v1.3
Powerboost 1000 Charger (500 wouldn't be enough)
Lipo battery (model and capacity to be decided)
Push buttons
More stuff to be added

I am open to any advice as this is my first 'proper' project.

Budget - £100

£40 for Batteries, Boosters and Buttons
£10 for the case (will be improvised or possibly laser cut to start with)
£30 for audio board and connectors
£30 for microphones

How the microphones will work

The Pi Portable Recorder will have a mic jack on the top of it where the user can simply plug in their own mic. The default will be to have the 'internal' mics plugged in just like the mics on the top of most portable recorder except the difference is they can be unplugged. This means the user can add a microphone suitable for their budget and use case from a Sennheiser ME 66 with K6 powering module down to a cheap lavalier mic found on Ebay for a few quid.

P.S. - Progress on the actual audio side will be slow until October 2018 which is when the Audio Injector Ultra 2 is delivered.
Last edited by KanoMaster22 on Fri Jul 06, 2018 9:32 pm, edited 3 times in total.

wh7qq
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Re: Pi Portable Recorder - Project Progress

Thu Jun 28, 2018 8:17 am

While I have not studied it deeply, it seems like the Ultra 2 probably saves to the same formats as the AudioInjector Stereo so why wait...just use the Stereo Card to get your project going and add the higher resolution formats and possibly greater battery capacity when the Ultra is released. You know what you are trying to achieve here and I do not but this looks like a time saver from what I can see. BTW, I was happy enough with the Stereo card performance to send a contribution to the new card's Kickstarter campaign.

KanoMaster22
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Re: Pi Portable Recorder - Project Progress

Thu Jun 28, 2018 3:47 pm

I have looked at this and the Stereo Soundcard seems to not have any TRS 1/8" (3.5mm) microphone jacks. This is the only thing I really need from the add on board I use for this project. If anyone has wired up a TRS microphone jack to a Raspberry Pi I would love to hear how.

Thanks,
LouisP

Note - I want high quality recordings so a USB adapter with 1/8" (3.5mm) mic jack will not do

wh7qq
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Re: Pi Portable Recorder - Project Progress

Thu Jun 28, 2018 5:01 pm

Did I understand you correctly?

The 3.5 mm jack on the RPi, AFAIK, is output only and would not accept a microphone. The input RCA jacks on the AudioInjector Stereo card would be the mic input and in that case, the tips of the RCA jacks can just be tied together to feed the tip of the TRS plug. Monophonic mic's usually use a "TS" plug as they have just a single "hot" connector and ground (sleeve). You might need a preamp on the mic output to drive the input...I have to use one for my MM phono pickup and the gain is still marginal but the mic may have a larger output. Flatmax has said that a resistor on the input of the stereo card can be removed or shorted (I don't recall which) to get more gain but I have not gotten up the courage to put the soldering iron to my card.

drgeoff
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Re: Pi Portable Recorder - Project Progress

Thu Jun 28, 2018 6:04 pm

It is virtually unheard of to use RCA phono sockets for microphone inputs. I've never seen any microphone with phono plugs. RCA sockets are invariably Line level (in or out).

My understanding is that the AudioInjector does not have external microphone inputs. It does have the option of a single mono electret capsule mounted on the PCB.

Frankly, if my goal was high quality I would not consider having a microphone level input on a HAT. Much too difficult to keep out the electrical noise from the RPI underneath.

And are you really going to end up with a device that is competitive in performance, size, battery life, ergonomics. ease of use etc compared to the many excellent devices in the £60 to £200 range from the likes of Sony, Olympus, Zoom, Teac etc?

wh7qq
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Re: Pi Portable Recorder - Project Progress

Thu Jun 28, 2018 7:04 pm

drgeoff wrote:
Thu Jun 28, 2018 6:04 pm
RCA sockets are invariably Line level (in or out).

My understanding is that the AudioInjector does not have external microphone inputs. It does have the option of a single mono electret capsule mounted on the PCB.
Most good quality phono hookups are well below line level but use RCA plugs/jacks (except, of course, for the USB plugs used on some of the newer turntables). The inputs and outputs on my phono preamp are RCA types. The RCA jacks are easy to hate...especially the older ones that are not gold plated...either too tight or too loose, oxidize easily and awkward to solder braid to the shield. When they are placed too close together for normal hands as with my Onkyo, they are a PITA to get in and out. But I have had poor results with the little 3.5 mm plugs and jacks as well.

Your understanding of the single mono mic on the AudioInjector is correct. Mine is earlier and does not have one...it may be an option. A single mic there seems a bit silly to me but it is not my interest anyhow.

The Kickstarter financed Ultra 2 has A-D and D-A capabilities that are equivalent to the best available and the preliminary specs are impressive with regard to noise floor and distortion. The proposed price is absurdly low. Still, very few can appreciate or need 192KHz/24 bit audio over the current CD standard. My septuagenarian ears certainly cannot.

KanoMaster22
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Re: Pi Portable Recorder - Project Progress

Fri Jun 29, 2018 6:43 am

Thanks for the help both of you. I thought I hadn't seen much RCA inputs before but maybe they are more popular in Australia (where Flatmax is based) or it could be that it was a requested feature. To answer drgeoff's question, I am aiming for my portable recorder to be similar (but possibly a bit worse) in performance to the likes of Zoom and Tascam etc. but this will be made up for by the hackability of the recorder. To start with the ergonomics will probably be a lot worse (possibly a laser cut case) than a normal portable recorder but I would hope to improve this over time. Drgeoff if you wouldn't have the input on a HAT then what would be your choice?

wh7gg thanks for the tips. Yes you did understand me correctly. Wiring the RCA input to a TRS jack is a good idea and I will probably try that method first. Yes the price seems low but it is the Kickstarter price and lots of Flatmax's other boards have been quite cheap and I have read a lot of people who are very impressed by the quality. The price is probably cheap due to only 1 or 2 people working on each project, limited time spent on documentation and the fact that there is not too much to the software side (although still stuff I couldn't code :D ).

wh7qq
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Re: Pi Portable Recorder - Project Progress

Mon Jul 02, 2018 8:09 pm

KanoMaster22 wrote: I thought I hadn't seen much RCA inputs before but maybe they are more popular in Australia (where Flatmax is based) or it could be that it was a requested feature.
RCA jacks are everywhere but they have vanished from BluRay players/recorders, are going away on TV receivers, never existed on smart phones and tend not to be used on pro gear as they are more noise prone than balanced inputs. They do go way back into the '40s and perhaps beyond so there is a lot of legacy gear about. My 8 year old Sony Bravia TV has them as does my equally old Onkyo stereo reciever.
KanoMaster22 wrote: To start with the ergonomics will probably be a lot worse (possibly a laser cut case) than a normal portable recorder but I would hope to improve this over time.
I modified a HighPi case https://www.amazon.com/gp/product/B0169 ... UTF8&psc=1 crudely to accommodate the RCA jacks and gain pots on the AudioInjector and the result is not perfect but looks ok. It might be a problem for cooling on a 3B but the 3B+ version has superior cooling so is probably ok. My 2B has no problem that way. There is also a RPi zero form factor version but it needs to have jacks and pots installed (from looking at the pics).

While the proximity to the main board is scary for all its computer hash, it seems not to be a problem for my ears. If it is a major concern, a short 40 pin jumper cable as used on the prototyping boards would provide plenty of separation. As for coding, none required at least at first, as alsaconfig, arecord and Audacity seem to do an excellent job of recording and saving to a file format of your choice...see the instructions on the forum. Audacity even lets you monitor the signal level on a live graph using an HDMI display.

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Imperf3kt
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Re: Pi Portable Recorder - Project Progress

Mon Jul 02, 2018 9:18 pm

I've got three RCA outputs on my Pi0
;)
They're still useful.
Stop plugging your fan directly into the GPIO 5v
https://www.electronics-tutorials.ws/power/transient-suppression.html

drgeoff
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Re: Pi Portable Recorder - Project Progress

Mon Jul 02, 2018 9:59 pm

wh7qq wrote:
Mon Jul 02, 2018 8:09 pm
KanoMaster22 wrote: While the proximity to the main board is scary for all its computer hash, it seems not to be a problem for my ears.
Line input levels on phono sockets are hundreds of millivolts. The output of microphones is typically hundreds of microvolts, ie 1000 times weaker. Thus the audibility of picked up noise is very much greater.

KanoMaster22
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Re: Pi Portable Recorder - Project Progress

Tue Jul 03, 2018 6:54 am

Thanks again for all your help everyone. Unfortunately, the High Pi case will not be big enough :cry: as I am going to be using a battery and oled as well in the build. I was looking for a case around 200mm x 90mm x 50mm. Audacity sounds good for my needs to start with. Can you adjust the recording level (is that the same as signal level) using Audacity? From what I see on Dr Geoff's post, the mic jacks only need a few millivolts. Does that mean I could get away with using the Adafruit Powerboost 500C instead of the 1000C?

Thanks,
LouisP
Last edited by KanoMaster22 on Tue Jul 03, 2018 2:54 pm, edited 1 time in total.

drgeoff
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Re: Pi Portable Recorder - Project Progress

Tue Jul 03, 2018 8:31 am

KanoMaster22 wrote:
Tue Jul 03, 2018 6:54 am
From what I see on Dr Geoff's post, the mic jacks only need a few millivolts. Does that mean I could get away with using the Adafruit Powerboost 500C instead of the 1000C?
No you have not understood at all and it does not bode well for the success of your project.

The signals from microphones are very weak. That means:

1. Microphone inputs need high amplification before being applied to an A to D converter.

2. Any noise picked up by the microphone circuitry before the amplification stage will also be amplified. It is the ratio of signal to noise at any point that is important. As the microphone signals are about 1000 times smaller than RCA inputs, the picked up noise and hash from the RPi, the Powerboost and the display needs to be kept about 1000 times smaller than when using line level inputs.

All that has no bearing on which Powerboost module.

KanoMaster22
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Re: Pi Portable Recorder - Project Progress

Tue Jul 03, 2018 2:36 pm

Thanks for the help and putting up with my lack of knowledge. I am not an expert in audio but have some decent knowledge and will probably learn a lot more through the course of this project. Stupid me getting volts and current mixed up. Well my understanding the Audio Injector comes with a good A-D coverter so it should do the job but my only concern is the size of the stack (Pi Zero, Audio Injector Ultra and Pre-Amp). Maybe I could have the Pi Zero and Audio Injector Ultra together and then wire them to the pre-amp which could be on top of the battery (depending on the thickness of the battery).

Edit - The battery I am looking at is 5mm thick so it should work.


drgeoff
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Re: Pi Portable Recorder - Project Progress

Wed Jul 04, 2018 5:50 pm

KanoMaster22 wrote:
Wed Jul 04, 2018 6:53 am
Could this (https://fe-pi.com/products/fe-pi-audio-z-v2) board be a good option?
You previously wrote: "Note - I want high quality recordings so a USB adapter with 1/8" (3.5mm) mic jack will not do."

Why do you think the fe-pi board would be better?

wh7qq
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Re: Pi Portable Recorder - Project Progress

Wed Jul 04, 2018 10:15 pm

drgeoff wrote:
Wed Jul 04, 2018 5:50 pm
You previously wrote: "Note - I want high quality recordings so a USB adapter with 1/8" (3.5mm) mic jack will not do."
Why do you think the fe-pi board would be better?
The fe-pi does look interesting and the V-IV version sports an array of RCA jacks and all have input A-D conversion but they do not say a word about codec used (V-IV), bit depth, sample rate and so on and none of these show up in my perusal of the data sheet for the SGTL5000 codec used in at least the Z V2. I am unsure if this is something to be concerned with or not. At $12 US, (before shipping info) it is worth a try even if it is junk. I have not seen a low cost USB based audio device that supports inputs of any kind but maybe that is just not a complete sample. I ordered the zero version just for fun so I will review it here if and when it arrives and I get it going. BTW, it came to $15.39 for USPS first class.

KanoMaster22
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Re: Pi Portable Recorder - Project Progress

Wed Jul 04, 2018 10:40 pm

DrGeoff note I said 'could this be better?' not stating that is was better. ;) Anyway, to answer your question Dr Geoff, it is supported in Raspbian no problem (with minor bit of well documented code), it quotes some decent specs (although not many specs are specified as noted by wh7qq) and it is a lot neater. I am based in the UK so unfortunately shipping is more than the actual product but I have contacted the seller and he says they will be listed on Amazon UK next month. Here are some things that might help wh7qq (although you have probably already found them):
https://www.pjrc.com/teensy/SGTL5000.pdf
https://github.com/raspberrypi/linux/pu ... e667e73d86
https://www.nxp.com/docs/en/user-guide/KTSGTL5000UG.pdf
https://cdn.shopify.com/s/files/1/0174/ ... 1820351421

These are mostly for other boards that use the same chip though. The last link looks the most promising and in-depth.

Thanks,
LouisP

wh7qq
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Re: Pi Portable Recorder - Project Progress

Thu Jul 05, 2018 7:17 pm

I had already seen the 1st-4th (identical data sheets) and was unable to find specs for bit depth or sample rate. There was a reference to 24 bit word length at one point but was not helpful. My old eyes glass over at long code references so the github info was not helpful (not enough snakes, chicken heads and rodents in my diet) ;) The remaining reference was concerning a development board that differs from the RPi quite a bit.

The proof of the pudding will be in the eating, as they say. I have two unused zeros lying around so I will put one of them to the task. We shall see. Also will be interesting to see about delivery...got a PayPal confirmation but nothing from the vendor yet. They may be down for the holiday weekend or ???

In the mean time, the AI Stereo board is alive and well and available cheaply on Amazon. I have found it to be quite satisfactory. It will be of some interest to compare Audacity tracks from the two devices. I do not have the hardware to test beyond that but Audacity will tell me about bit depth on the input and the traces on identical inputs should tell us about distortion and SN ratio if discernable.

KanoMaster22
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Re: Pi Portable Recorder - Project Progress

Thu Jul 05, 2018 9:43 pm

The only reason I haven't grabbed an Audio Injector Zero of Amazon is that it doesn't have a 3.5mm mic jack as mentioned in a previous post. As far as I know, the AI Zero supports stereo audio if you can wire up a suitable jack somehow.

drgeoff
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Re: Pi Portable Recorder - Project Progress

Thu Jul 05, 2018 10:11 pm

The OP allocated £20 for microphones. Note the plural, so we must assume he wants stereo. None of those boards have stereo mic preamps. Doesn't matter how good the A to D converters are, if the mics are rubbish and the preamps are picking up mush from the RPi, those factors will limit the quality.

If you want to spend the time and money learning how hard it is then go ahead. If you want a good portable recorder spend the £70 on a Zoom H1 or H1n or look around at what is available within your budget.

wh7qq
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Re: Pi Portable Recorder - Project Progress

Thu Jul 05, 2018 10:54 pm

Most of the projects one can think of with the RPi can be accomplished as or more cheaply with something off the shelf and the Zoom H1 is no exception...nice package if that is what you want. They actually do publish some specs in the manual. Similar packages from TASCAM and others are in the same category. If you already have the RPi and accessories and want to put it to serious work without a big cash outlay, or just want to be able to say "I did it" or want to learn more about a topic, the RPi is a good starting point.

I have several projects working around the house that could be easily done by off the shelf devices but when you put together the overall versatility of the RPi and the ability to manage it online, you can get exactly what you want and no extras or compromises and add features as the need or fancy arises. In this case, if you are a professional musician or recordist, the handy, pocketable devices are great. That is one reason why much of the world doesn't even know what an RPi is, let alone own one or use it.

My out of date signature, below, suggests I am using a 3B for this...used to be true but I recently acquired an Asrock j3455-itx board that uses the same amount of power in standby mode as the 3B, has 4 gig of memory and runs a full load copy of Mint 19 Xfce4. It is now my hardware choice although the 3B still hangs on the back of my monitor by a VESA mount. Nice not to have the 1G memory limitation that locked me up if I opened too many browser windows. So does that mean the RPi has no value? Not at all. It will get used for another project that will exploit the I/O versatility of the GPIO connector (that might also have an off the shelf competitor or two). It all depends on what you want/need.

drgeoff
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Re: Pi Portable Recorder - Project Progress

Thu Jul 05, 2018 11:08 pm

wh7qq wrote:
Thu Jul 05, 2018 10:54 pm
... when you put together the overall versatility of the RPi and the ability to manage it online, you can get exactly what you want and no extras or compromises and add features as the need or fancy arises.
Agreed but with a big proviso. You need to have or acquire sufficient knowledge to accomplish it. In this case, the OP does not and it isn't the sort of project that just needs some forum replies to remedy that.

wh7qq
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Re: Pi Portable Recorder - Project Progress

Fri Jul 06, 2018 12:48 am

Y'know, that may be true but on the other hand, discounts the "fun" of learning something new and the chance that something might come of it. Life is funny that way.

Many years ago, I took on a project that from my ignorance, thought would be easy...just a few relays and microswitches and a motor. A year or so later, it took over my garage and more of my disposable income than my wife liked. But with a good working prototype built, I was able to sell the idea and a well known name in the field started building it. In this case, there was another product out there already but ours took over the major market share. We moved to a nicer home with the proceeds and my wife quit complaining and never bothered me again about my "projects".

Years later, I went to work for a subsidiary of a major manufacturer developing a prototype product to fill a related need. The corporate PhD's had a similar project with a big budget going so it was decided to run the proto's head to head. I cobbled up a program in Turbo Pascal (no programmer am I) along with a lugable 286 PC and our prototype and flew across the country for this demo. The corporate folks had tens of thousands invested in Zeiss equipment to do the job and still had to take their data to a computer for crunching, while we had real numbers on display on the lugable. Our POS won hands down and corporate backed production.

But we are far afield of the topic here and even if only as an exercise in learning for the OP, it probably should not be naysayed. For me, it takes me back to my first Dynaco kit amp. What a kick when I powered it up for the first smoke test and it worked!

KanoMaster22
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Re: Pi Portable Recorder - Project Progress

Fri Jul 06, 2018 6:05 am

I actually already have a Zoom H1 and made my first recordings on it last week (listen to unedited Nightjar recording linked at end) but I hope this project will help me learn more about audio. Once I have selected a suitable audio board there can’t be much on the audio side to do except plug in the mic and select some appropriate settings. The hardest bit will probably be coding it so I can adjust the recording level.

Thanks,
Louis

Edit - A mic budget of £30 is probably more realistic.

https://drive.google.com/file/d/1_V93Mb ... sp=sharing

KanoMaster22
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Re: Pi Portable Recorder - Project Progress

Fri Jul 06, 2018 9:25 pm

This is probably all wrong, but would the Audio Injector Ultra 2 be suitable for bat recording as well as bird recording (obviously altering the settings for each one though)? I think you would need a different microphone for this if can do it though. The Kickstarter says
The sound card is ultrasound because it can output/input analogue frequencies extending up to the ultrasonic frequencies. Such high frequencies require a digital 192 kHz sample rate
I have no knowledge at all on bat detectors but someone showed me one when I was testing my Zoom H1 and it was pretty cool listening to a bat so I was thinking it could possibly be an extra for the Pi Portable Recorder (depending if I use the Audio Injector Ultra 2 though).

Thanks,
LouisP

Edit - Check the updated original post.

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