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  1. #1
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    Instructions for connecting USB DAC to Touch

    OK, here finally are my official instructions for connecting a USB DAC up to the Touch.

    A few words up front: this is not officially endorsed by Logitech, if you have questions about this, don't bother Logitech support, they won't have any idea what you are talking about. This is NOT plug and play, you have to go in and edit a file on the Touch, once you do that, you cannot get music out of any other output, it will ONLY send music to the USB DAC. You have to go in and restore things to the way they were in order to get music out of any other output. The setup will be different depending on whether you plug the DAC in after bootup (known as hotplugging) or already plugged in when booting. Choose which way you want to go and ALWAYS do it that way! (if you forget and get it wrong, it won't hurt anything, you just won't get any music out) Due to some weirdnesses in the way USB DACs are seen by the Touch, the UI beeps and other sounds will usually be turned off when a USB DAC is plugged in. But not always.

    Not all USB DACs will work with the Touch. If the DAC requires a custom driver, it will NOT work with the Touch. Only DACs that can be used with generic USB drivers will work. If your DAC can only play up to 48KHz sample rate you may have problems playing 88.2 or 96 files. The server thinks the Touch can go up to 96, but if the DAC can only go up to 48, the linux software on the Touch will do the down conversion, which takes a fair amount of horsepower and may cause problems with playback.

    One other thing, its probably not a good idea to use a USB DAC if you are also using a USB disk plugged into the Touch to store the music files. Since there is only one USB port you will need a USB hub, putting both the storage and the DAC on the same port is probably not a good idea, it may work, it may not. Be prepared to use an external server over a network.

    So if you are still willing to give this a try, here are the details.

    You will need to SSH into the Touch. In order to do this you will need an SSH client running on a computer on your network. On windows this is called PuTTy, its free, you can find it on the web. For Mac OSX its builtin, called SSH.

    PuTTy is a regular windows GUI program, when you bring it up you type in the IP address of the Touch, press <enter>. It will then ask for the user, type in root<Enter>. Then it asks for the password. (See below)

    For SSH on OSX you have to start a command window, then type:
    ssh -l root <IP address>
    It will then ask for the password.

    To SSH into the Touch you have to turn remote access on, this is done with
    settings->advanced->Remote access

    Touch the "enable remote access" line, you should see the little square go blue. You will also get a popup which gives the IP address and the password, write these down. These will be used when you SSH into the Touch.

    Now plug the USB DAC into the Touch and reboot the Touch (or reboot and plug the DAC in) Pull the power plug and reinsert it to reboot.

    When up and running SSH into the Touch (see above). (for each line you see in these instructions type <Enter> at the end of the line)
    Type:

    aplay -l
    (thats dash ell)

    This gives you a list of the audio devices on the Touch. You should see the USB DAC. Each device will have a line starting with
    card <number> <name>
    such as
    card 3 USB <lots of other stuff>
    The name is the one you want to write down. In this case it was USB. It might be something such as "default". In this case the rest of the line will let you know its the USB DAC.

    Then type:

    cd /etc
    cp asound.conf asound.conf.orig
    sync


    Now you are going to create a new config file. The only editor available is "vi", which is very weird to use if you have not used it before. It runs in a display mode (default)and an insert mode. You get into insert mode by tapping the 'i', type stuff you want, then tap <ESC> to get out of insert mode. When in display mode tapping 'x' will delete the character the cursor is under. Tapping 'dd' will delete a line. That should be enough to edit this simple file. In the file below replace <name> with the name you wrote down in the previous step. For example
    card USB;

    Type:
    vi asound.conf.usb

    tap 'i', type:

    pcm.usbdac {
    type hw;
    card <name>;
    }
    pcm.plugusb {
    type plug;
    slave.pcm "usbdac";
    }
    ctl.plugusb {
    type hw;
    card <name>;
    }

    pcm.!default plugusb

    Tap the <ESC> key
    type:
    :wq<enter>
    (thats <colon><w><q><enter> don't forget the colon)
    To quite without writing anything type:
    :!q<enter>

    This will write the file and quit.

    Then type:
    cp asound.conf.usb asound.conf
    sync
    sync

    (the syncs make sure memory buffers get written to disk)

    Type:
    exit

    This gets you out of SSH.

    At this point reboot the Touch and the music should now play through the USB DAC. Since you explicitly told the music to go to the USB DAC you won't have any sound when the USB DAC is not connected to the Touch. To get back to normal you have to SSH back into the Touch and type:

    cd /etc
    cp asound.conf.orig asound.conf
    sync
    sync
    exit

    And reboot. You should now be back to normal.

    If things get so badly messed up you don't know what to do you can always do a factory reset which will undo all this.

    Thats about it. Have FUN!

    PS, there IS a way to get music out of all the other outputs and a USB DAC at the same time, but its a WAY more complicated setup, I decided NOT to post that.

    John S.

  2. #2
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    Many thanks to John for the new version!

    I followed step by step your instructions. It worked like a charm.
    My DAC: MF V-DAC

    Alex
    Greece

  3. #3
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    possible 192/24 "shortcut"?

    John, I also own the V-DAC which, by-the-way is 192/24 capable... Right now I run it through the coax. Do you think connecting it through USB as described would circumvent some of the problems still staying in the way of playing 192/24 through the Touch? (that you mentioned in another thread http://forums.slimdevices.com/showpo...93&postcount=9)

    If so, what would be the steps to be taken?

    Thanks for so many interesting thoughts in this forum.
    Ovidiu

  4. #4
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    Quote Originally Posted by Ovidiu View Post
    John, I also own the V-DAC which, by-the-way is 192/24 capable... Right now I run it through the coax. Do you think connecting it through USB as described would circumvent some of the problems still staying in the way of playing 192/24 through the Touch? (that you mentioned in another thread http://forums.slimdevices.com/showpo...93&postcount=9)

    If so, what would be the steps to be taken?

    Thanks for so many interesting thoughts in this forum.
    Ovidiu
    Hm, thats going to be tough. It depends on HOW the DAC implements 192. IF it uses a custom driver its not going to work. IF it uses USB audio class 2 its not going to work (the version of ALSA in the Touch just has audio class 1 not 2). The only way it could work is if the DAC uses high speed bus mode and uses audio class 1 protocol. This will actually work, but is not officially anything.

    Audio class 1 does not specifiy high speed mode and does not officially support 192 but the way the ALSA driver were written its perfectly happy using high speed mode. The class 1 protocol does not explicitly support 192, but it doesn't preclude it either. If the hardware sets the values right for 192 it will actually work. Unfortunately I don't know of any hardware that actually works this way, SO, the probability of this working is pretty low.

    If Logitech would switch to the latest ALSA that DOES have support for audio class 2 so a DAC designed to work with that would work. But I don't see Logitech doing that any time soon.

    John S.

  5. #5
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    a bit contentious (probably ), but a genuine question.
    Any improvements over SPDIF usng USB into a suitable Dac?

    Not so much for my Caiman dac, the usb max's at 16/44, but maybe for others?

  6. #6
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    Quote Originally Posted by Gazjam View Post
    a bit contentious (probably ), but a genuine question.
    Any improvements over SPDIF usng USB into a suitable Dac?

    Not so much for my Caiman dac, the usb max's at 16/44, but maybe for others?
    There is no way to make a generic statement on that, its going to be all over the place.

    Many DACs that have both S/PDIF and USB inputs use a USB to S/PDIF converter and feed it into the S/PDIF input under the hood. In this case the USB input is probably going to be worse. (but not necessarily always so, again it depends on many other factors)

    There are several USB input implementations that are REALY good, and these could easily outperform a run of the mill S/PDIF implementation. A designer that uses one of these good USB circuits is probably also going to use a good S/PDIF implementation as well, so there may not be very much difference between the two on THAT box. But between different boxes it could go either way.

    John S.

  7. #7
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    thanks John, good info as always.

    Need to check up WHICH usb implementation my Caiman has...
    I dont have a lot of 24/96 stuff, so might be worth investigating as a possible tweak.

    Whats the "good" usb implementation to look for John?
    (I can probably ask the Dac designer direct on another forum..)

    Sorry!
    Last edited by Gazjam; 2010-09-22 at 12:51.

  8. #8
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    Well I found a small glitch.

    Squeezebox Touch + V-DAC

    No matter what I play (16/44 or 24/96 ), I get some audible clicks and pops (vinyl like). Otherwise it sounds great ...

    I've changed USB cable but it didn't make any differnce.

    Also I checked between wireless and ethernet, again without luck.

    When using coax or optical input it works all right.

    Alex

  9. #9
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    Quote Originally Posted by avous View Post
    Well I found a small glitch.

    Squeezebox Touch + V-DAC

    No matter what I play (16/44 or 24/96 ), I get some audible clicks and pops (vinyl like). Otherwise it sounds great ...

    I've changed USB cable but it didn't make any differnce.

    Also I checked between wireless and ethernet, again without luck.

    When using coax or optical input it works all right.

    Alex
    Do you know if the V-DAC uses asynchronous USB or adaptive USB? The USB driver in the Touch has a problem with some asynchronous implementations. I've sent a fix to the Logitech developers but I don't think its ever been put in a firmware.

    John S.

  10. #10
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    Quote Originally Posted by Gazjam View Post
    thanks John, good info as always.

    Need to check up WHICH usb implementation my Caiman has...
    I dont have a lot of 24/96 stuff, so might be worth investigating as a possible tweak.

    Whats the "good" usb implementation to look for John?
    (I can probably ask the Dac designer direct on another forum..)

    Sorry!
    John?(or other USB experts?)
    Can I bother you to scan your eye over this please, just a general recommendation if you would?

    The USB chip in my Dac is THIS one:
    PCM2902E

    The Dac design has a seperate reclocking circuit just for USB...

    1. Would this make the positive difference making this Touch USB mod worth doing?
    2. Would this USB mod negate the SSH mods switching off services, turning off wifi etc.in the Touch, which I found to make a positive improvement?

    USB Chip Specs:

    SINGLE-ENDED ANALOG INPUT/OUTPUT AND S/PDIF
    – Pass-Band Ripple = ±0.1 dB
    234· PCM2900: Without S/PDIF – Stop-Band Attenuation = –43 dB
    · PCM2902: With S/PDIF – Single-Ended Voltage Output
    · On-Chip USB Interface: – Analog LPF Included
    – With Full-Speed Transceivers · Multifunctions:
    – Fully Compliant With USB 1.1 Specification – Human Interface Device (HID) Volume ±
    – Certified by USB-IF Control and Mute Control
    – Partially Programmable Descriptors (1) – Suspend Flag
    – USB Adaptive Mode for Playback · Package: 28-Pin SSOP
    – USB Asynchronous Mode for Record
    – Bus Powered · USB Audio Speaker
    · 16-Bit Delta-Sigma ADC and DAC · USB Headset
    · Sampling Rate: · USB Monitor
    – DAC: 32, 44.1, 48 kHz · USB Audio Interface Box
    – ADC: 8, 11.025, 16, 22.05, 32, 44.1, 48 kHz
    · On-Chip Clock Generator With Single 12-MHz
    Clock Source The PCM2900/2902 is Texas Instruments' single-chip
    · Single Power Supply: 5 V Typical (VBUS) USB stereo audio codec with USB-compliant
    · Stereo ADC full-speed protocol controller and S/PDIF . The USB protocol controller works with
    – Analog Performance at VBUS = 5 V no software code, but the USB descriptors can be
    – THD+N = 0.01% modified in some areas (e.g., vendor ID/product ID).
    – SNR = 89 dB The PCM2900/2902 employs SpAct™ architecture,
    – Dynamic Range = 89 dB TI's unique system that recovers the audio clock from USB packet data. On-chip analog PLLs with SpAct
    – Decimation Digital Filter architecture enable playback and record with low
    – Pass-Band Ripple = ±0.05 dB clock jitter and with independent playback and record
    – Stop-Band Attenuation = 65 dB sampling rates.
    – Single-Ended Voltage Input
    – Antialiasing Filter Included
    – Digital LCF Included
    · Stereo DAC
    – Analog Performance at VBUS = 5 V
    – THD+N = 0.005%
    – SNR = 96 dB
    – Dynamic Range = 93 dB
    – Oversampling Digital Filter

    http://nl.mouser.com/Search/ProductD...mJPSH2QDmALg==

    Thanks for any information!
    Last edited by Gazjam; 2010-09-23 at 14:29.

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