Cm6206 Sound Card
Anita Damelio
If you wish to start a YouTube or Twitch career, transfer your old audio cassette recordings or vinyl collection to your computer, C-MEDIA CM6206 External USB Sound Card is a very nice solution in case you use a modern laptop without integrated multi-channel audio card and dedicated Line-In or MIC inputs. This card can be bought really cheap on Amazon, AliExpress, BangGood and similar online stores, and have it delivered for free in few days or weeks.
However, engineers who designed and manufactured this sound board crippled LINE-IN analog recording inputs frequency response in low / bass section by putting very small coupling capacitors! Why oh why ???
CM6206 hardware is perfectly capable going all the way down to a sub-hertz (less than 1 Hz) flat frequency response if desired / required. You can even bypass input AC coupling capacitors to enable DC input, with some precaution (useful for audio oscilloscope applications and DC signal measurements e.g. using Daqarta software).
C-MEDIA CM6206 audio codec is used in many different sound cards, including 7.1 surround models. It supports separate Headphone output, mute, rec mute, digital volume controls, dual mono MICROPHONE inputs and more! Of course, in this 5.1 model not all the features are used (obvious cost reduction saving on external parts and components), but what can you expect from a $5 or $10 sound card? More expensive $20 models come with 7.1 audio, dedicated headphones output, dual MIC and LINE-IN inputs, Volume and Mute controls, but those are not really essential, as you can achieve the same in software, although they can be convenient as dedicated hardware buttons.
In this video I have upgraded input coupling capacitors with larger values and improved frequency response considerably! In the end of the video is a line-in recording example using C-MEDIA CM6206 5.1 External USB Sound card with and without this modification compared to the original audio, along with the frequency response charts.
You should avoid recording at high levels near 0 dB (+/- 1.40 Volts) anyway, to avoid clipping. Remember, DC offset in audio is bad because it effectively reduces available dynamic range and maximum signal input voltage span.
I want to use it to measure some speakers, and TS parameters, with Art / Limp, Rew. I use a Dayton imm-6 microphone for measurement. I also have others calibrated, but I wanted to compare after replacing the capacitors with a Presonus card of 100 Euro + microphone Sonarworks ref 20, calibrated.
Hi! Thanks for your upgrade recommendation. They are helpful. My question is whether film capacitors like WIMA MKP (polypropylene) would be a better alternative to electrolytic caps? They are not prone to aging and are actually more often used in high-grade audio applications.Thanks!
For the low signal coupling inputs, again, yes, in theory, those MKPs (or cheaper MKTs) would be great, but they do not affect the signal much beyond the inherent high-pass filtering (RC resonant circuit), and because the signal is low power kind, losses in capacitors are your least concern.
You cannot improve AD and DA converters merely by upgrading input or output coupling capacitors! The signal will still be the same, limited by converter precision, quantization noise, jitter etc. Bottom line, buy another more powerful DSP audio card, instead of capacitors in that case. You will just waste your money on the wrong items otherwise.
I would suggest to try drivers that come with this card on a mini disc (mini CD), that should at least give you native control over SPDIF and gain, something which seems not possible with generic USB Audio drivers (assuming you use Windows, but it could be the same issue on Linux and Mac).
Try replacing both ceramic and polymer capacitors at line input with film. There are relatively small and inexpensive 63v models available. It can significantly reduce input dc offset due to much lower leakage current of such caps.
Another thing is that DC offset is probably caused by poorly balanced (uncompensated) input stage inside C-MEDIA chip itself, and I seriously doubt that external capacitor alone can eliminate it or make a noticeable improvement, but I could be wrong.
On the version of the PCB that I have, C14 is not populated. I can see from your photos it is present, but from the angle the photos are taken I cannot read the value from them. Could you tell me what is fitted to C14 on your PCB?
I got reports that some recent CM6206-based devices seem to be configured differently and work out-of-the-box, so it is worth trying whether you can get sound out of your new device before installing this enabler.
There is a saying: there is no such thing as a free lunch, and it also applies to these cheap sound cards. Whatever money you save compared to a more expensive major brand card, you may pay back in time wasted due to the poor quality of these cards and lack of proper operating system support. Therefore a few things to check first:
You need OS X 10.5 or newer to make this work. It should work in 10.8, unless perhaps you enabled GateKeeper. Thanks to a donation by Mark Hempelmann I was motivated enough to wrap this program in a fully automatic daemon. All you need to do is run the installer and reboot, and your sound card should work. With that I mean you should get sound from it, but whether you can get surround from it depends entirely on whether your OS X sound settings are properly configured.
The source code (ZIP archive) is also available. Mind that I myself have not used the CM6206-based sound card for several years. Instead I bought a proper hardware 5.1 decoder connected through S/PDIF, which avoids all the problems with Audio MIDI Setup, lack of proper multi-channel support, and bugs in media players. It is possible this enabler will not work in the most recent Mac OS X versions. If this is the case, your best option is to download the source code and try to fix it yourself, because my motivation to work on this enabler is very low.
Unfortunately, at the time of this writing it is still quite a hassle to get surround sound properly set up on OS X. Therefore I made a checklist of what you should do to get 5.1 sound out of any multi-channel sound card:
To test if all channels work, you can download the following AC3 test sound. You could also use it to roughly calibrate the volumes for each channel on your audio system.
Download 5.1 channel test file (ZIP archive)
VLC also has multi-channel output, but it is dodgy. The balance (volume) between center/front/surround tends to change with each movie you play, making it impossible to calibrate your setup. I suspect 5.1 streams (AC3, DTS) to contain a relative gain parameter for the rear/center channels which is ignored by VLC, causing the annoying changes in volume.
Many people seem to be confused about the difference between sending surround sound as passthrough (through S/PDIF) and playing it as six or eight separate channels. As I have explained elsewhere, these are two entirely different situations. With this specific sound card you can do both, although on a regular Mac you do not need a USB sound card to do optical passthrough: simply use a tiny 3.5mm adaptor to connect a Toslink cable directly to the Mac's built-in line out port.
The CM6206 is not able to decode AC3 or DTS streams. It is a simple sound card with 6 or 8 output channels and a few input channels. Plugging an optical cable into the S/PDIF input if your card has one, will not cause decoded audio to come out of the outputs, nor can you get multi-channel output by sending an encoded 5.1 stream from your Mac, this will only produce noise on the Front channel. The software you use must support built-in 5.1 decoding to get multi-channel output out of your sound card. For instance VLC and the most recent version of Plex support it. There is no software that I know of, that can decode a Dolby or DTS signal coming in through the optical input and send the audio to the card's outputs (although in theory this could be possible).
To be honest, I do not recommend this kind of sound card to anyone who wants to get hassle-free surround sound on their Mac. These cards are most useful to people who want multiple sound channel output for special applications. But for simple 5.1 sound they are a pain in the ass because only few programs support them, and the ones that do often have bugs (e.g. VLC). If you want to connect your Mac to a surround system and you are doubting whether to buy either a multi-channel card like this or a stand-alone surround decoder connected through HDMI or S/PDIF, I can only recommend the latter. A stand-alone decoder will work without having to fiddle with complicated system settings or tweaking volume knobs with every new film you watch. On top of that, it has the added advantage that it can also be connected to any other device that has an HDMI or S/PDIF output.
The most sensible way to get encoded surround sound to an external device these days is through a HDMI cable. If you have a device with only an S/PDIF input, you can use a HDMI audio extractor that has an S/PDIF output.
[UPDATE 18/02/18] This may not be as straightforward as I thought. I have bought one of these for its S/PDIF input (TOSLink, actually). This works (being driven by a 30-year old CD player for testing), but it has focused my mind on the problem of sample clock drift:
It would be possible to calculate on-the-fly a new, exact kernel for every new sample, but this would be very processor intensive, involving many calculations. Instead, it is possible to pre-calculate a range of kernels that represent a few fractional positions between adjacent samples. In operation, the two kernels on either side of the desired non-integer sample time are swept and accumulated, and then linear interpolation between these two values used to find the value representing the exact sample time.
You may be horrified at the thought of linear interpolation until you realise that several thousand kernels could be pre-calculated and stored in memory, so that the error of the linear interpolation would be extremely small indeed.
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