synthv1_jack: command not found

Maybe Your $PATH variable doesn't contain the default paths? echo $PATH should give something like:

[root@server ~]# echo $PATH
/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin

If it's empty, You may set the PATH variable with this command

export PATH="/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin"

On Debian possible default full paths are:

/usr/bin/synthv1_jack - from package: synthv1

You may install the required package with command apt-get install {package}

Error in other languages:
synthv1_jack: bevel nie gevind nie
synthv1_jack: comandă negăsită
synthv1_jack: comando não encontrado
synthv1_jack: commande introuvable
synthv1_jack: command not found
synthv1_jack: käsku ei ole
synthv1_jack: không tìm thấy lệnh
synthv1_jack: komanda nerasta
synthv1_jack: Kommando nicht gefunden.
synthv1_jack: kommandot finns inte
synthv1_jack: komut yok
synthv1_jack: nie znaleziono polecenia
synthv1_jack: níor aimsíodh an t-ordú
synthv1_jack: no se encontró la orden
synthv1_jack: no s'ha trobat l'ordre
synthv1_jack: opdracht niet gevonden
synthv1_jack: parancs nem található
synthv1_jack: perintah tidak ditemukan
synthv1_jack: príkaz nenájdený
synthv1_jack: příkaz nenalezen
synthv1_jack: команда не найдена
synthv1_jack: командата не е открита
synthv1_jack: 命令找不到
synthv1_jack: コマンドが見つかりません